Acute Retention Of Urine
Acute retention of urine is the sudden inability to pass urine voluntarily, resulting in painful distension of the bladder that requires urgent catheterization.
History Taking: Acute Retention of Urine (AROU)
This is your first job. Before you launch into differential diagnosis, you need to establish that the patient actually has a full bladder they cannot empty, rather than simply not producing urine.
Key Questions
| Question | Why It Matters | Cantonese Phrasing |
|---|---|---|
| "When did you last pass urine?" | Establishes timeline and acuity | 你上一次小便係幾時？(nei5 soeng6 jat1 ci3 siu2 bin6 hai6 gei2 si4?) |
| "Is your lower tummy swollen and painful?" | Painful suprapubic distension = AROU; painless = CROU [1][2] | 你個肚下面有冇脹住痛？(nei5 go3 tou5 haa5 min6 jau5 mou5 zoeng3 zyu6 tung3?) |
| "Are you still producing urine at all — even small amounts or dribbling?" | Differentiates retention from anuria/oliguria [2][3] | 你仲有冇少少尿出到？(nei5 zung6 jau5 mou5 siu2 siu2 niu6 ceot1 dou2?) |
| "Is this the first time, or has this happened before?" | First episode vs recurrent — recurrent suggests progressive pathology [1] | 係第一次定之前都試過？(hai6 dai6 jat1 ci3 ding6 zi1 cin4 dou1 si3 gwo3?) |
AROU vs Anuria — Don't confuse them
AROU should be distinguished from anuria or oliguria → lack of urine production, not retention [2][3]. A patient in shock (e.g. ruptured AAA) or dehydration may also not be passing urine, but the bladder will be empty. Always confirm with a bladder scan (≥300mL unable to void suggests retention; ≥1L suggests chronic retention) [2].
2. Characterizing the Current Episode
- "When exactly did you stop being able to pass urine?" — Pin down the hour/day. Sudden onset over hours = acute. Gradual worsening over days-weeks with vague fullness = more likely chronic with acute-on-chronic overlay.
- "What were you doing when it started?" — Post-operative retention is extremely common after GA or epidural anaesthesia [3][4].
This is a high-yield area in the OSCE. There is almost always a precipitant on top of a background predisposition.
| Precipitant | Question to Ask | Cantonese |
|---|---|---|
| Recent surgery / anaesthesia | "Have you had any operations recently?" | 你最近有冇做過手術？(nei5 zeoi3 gan6 jau5 mou5 zou6 gwo3 sau2 seot6?) |
| New medications | "Have you started any new medications — especially cold medicines, painkillers, or psychiatric drugs?" | 你有冇食新藥？特別係傷風藥、止痛藥？(nei5 jau5 mou5 sik6 san1 joek6?) |
| Alcohol | "Have you been drinking large amounts of alcohol recently?" | 你最近有冇飲好多酒？(nei5 zeoi3 gan6 jau5 mou5 jam2 hou2 do1 zau2?) |
| Constipation / faecal impaction | "When did you last open your bowels?" | 你上次大便幾時？(nei5 soeng6 ci3 daai6 bin6 gei2 si4?) |
| Prolonged immobility | "Have you been bedbound or less mobile recently?" | 你最近有冇長時間臥床？ |
| Pelvic trauma | "Have you had any injury to your lower tummy, back passage, or groin?" | 你有冇撞親下面？ |
Cold medications — a classic OSCE trap
3. Identifying the Underlying Cause
Ask about preceding Lower Urinary Tract Symptoms (LUTS) [1][5]. Use the IPSS framework:
Voiding (Obstructive) Symptoms — point to outlet obstruction:
- Hesitancy (遲遲先開始 ci4 ci4 sin1 hoi1 ci2) — "Do you have to wait a long time before urine starts flowing?"
- Weak stream (尿流好細 niu6 lau4 hou2 sai3) — "Is your urine stream weaker than before?"
- Straining — "Do you have to push or strain to start urinating?"
- Intermittency / Dribbling — "Does your stream stop and start?"
- Incomplete emptying — "After you finish, do you feel like your bladder is still not empty?"
Storage (Irritative) Symptoms — may coexist:
- Frequency — "How many times do you go during the day?" (>8/day is abnormal)
- Urgency — "Do you get a sudden strong urge that's hard to hold?"
- Nocturia — "How many times do you wake at night to pass urine?" (夜尿幾多次 je6 niu6 gei2 do1 ci3)
Why IPSS matters: IPSS can be used for males [2] to quantify symptom severity (0–7 mild, 8–19 moderate, 20–35 severe) [4]. This helps grade BPH severity and guides management decisions.
BPH is the most common cause of AROU in males (53%) [2][3]. Ask about complications:
| Complication | Question | Why |
|---|---|---|
| Gross haematuria | "Have you noticed blood in your urine?" (有冇血尿 jau5 mou5 hyut3 niu6) | Suggests BPH, CA bladder, or CA prostate [1] |
| UTI (fever/dysuria) | "Any burning when you pass urine? Any fever?" | Stasis predisposes to infection [1] |
| Bladder/urethral stone | "Any sudden sharp pain when urinating that makes you stop mid-stream?" (strangury) | Stones can cause BOO or complicate BPH [1] |
| Renal impairment | "Any nausea, loss of appetite, itching, or fatigue?" (uraemic symptoms) | Obstructive nephropathy from chronic retention [1][2] |
This is the one you cannot miss. Neurogenic bladder can present as AROU, and if spinal cord compression is the cause, delay in diagnosis → irreversible paraplegia [3][4][6].
| Question | What You're Looking For | Cantonese |
|---|---|---|
| "Any back pain?" | Vertebral metastasis, epidural abscess, disc prolapse | 有冇背脊痛？(jau5 mou5 bui3 zek3 tung3?) |
| "Any weakness or numbness in your legs?" | Motor/sensory deficit from cord compression | 對腳有冇冇力或者痺？(deoi3 goek3 jau5 mou5 mou5 lik6 waak6 ze2 bei3?) |
| "Any numbness around your back passage/saddle area?" | Saddle anaesthesia → cauda equina syndrome | 屎窟附近有冇痺？ |
| "Any problems with bowel control?" | Faecal incontinence = red flag for cauda equina | 有冇失禁？ |
Drug-induced AROU is extremely common and very testable [2][3][4]:
| Drug Class | Mechanism | Examples |
|---|---|---|
| Sympathomimetics (α-agonists) | ↑Urethral smooth muscle tone → ↑outflow resistance | Phenylephrine (cold medications), pseudoephedrine |
| Sympathomimetics (β-agonists) | Detrusor relaxation | Terbutaline, salbutamol (bronchodilators) |
| Anticholinergics | Impair detrusor contractility | Atropine, ipratropium, tiotropium, antihistamines (promethazine), antispasmodics (opioids) |
| Antipsychotics | Anticholinergic side effects | Chlorpromazine, olanzapine |
| Antidepressants | Anticholinergic / serotonergic effects | TCAs (amitriptyline), SSRIs |
| Disopyramide | Anticholinergic (class Ia antiarrhythmic) | Disopyramide |
| MDMA (Ecstasy) | Sympathomimetic | Recreational drug use |
Ask specifically: "Are you taking any cold medicines, cough syrups, asthma inhalers, sleeping tablets, pain medications, or psychiatric medications?" (你有冇食傷風藥、咳藥水、哮喘噴劑、安眠藥、止痛藥、精神科藥？)
| Question | Target |
|---|---|
| "Any unexplained weight loss or loss of appetite?" | Constitutional symptoms for CA prostate, CA bladder [4] |
| "Any bone pain, especially in the back or hips?" | Bony metastases from prostate CA |
| "Any blood in your urine — when does it appear?" | Haematuria — beginning = lower tract, throughout = above bladder, terminal = prostate/bladder neck [7] |
| "Have you ever worked with chemicals, dyes, or rubber?" | Occupational risk for bladder CA |
| System | Questions | Relevance |
|---|---|---|
| Urological | Dysuria, haematuria, urethral discharge, scrotal pain | UTI, STD, urethritis causing urethral oedema |
| GI | Constipation, change in bowel habit, rectal bleeding | Constipation (7.5% of male AROU) [2]; rectal mass |
| Neurological | Back pain, limb weakness, sensory changes, gait difficulty | Cord compression, cauda equina, MS, GBS |
| Constitutional | Fever, weight loss, night sweats, fatigue | Infection, malignancy |
| Gynaecological (females) | Pelvic heaviness, prolapse symptoms, vaginal bleeding | Pelvic organ prolapse (cystocele, rectocele), gynaecological tumours [2][3] |
5. Background History
- BPH — duration, previous IPSS, previous treatment (alpha-blockers, 5-ARI)
- Diabetes mellitus — DM neuropathy is a key cause of neurogenic bladder [1][2][6]
- Stroke / Parkinson's disease / Multiple sclerosis — neurogenic bladder [2]
- STDs — urethral stricture from previous gonococcal urethritis [2]
- Malignancy — especially prostate, bladder, any pelvic/spinal tumour
- Pelvic trauma
- Go through the drug classes above systematically
- Drug allergies — especially to local anaesthetics and antibiotics (relevant for catheterization and treatment)
- Family history of prostate cancer [5] — first-degree relative with prostate CA doubles risk
- BPH tends to run in families
- Smoking — risk factor for bladder CA [7]
- Alcohol — excessive fluid intake (especially alcohol) can precipitate AROU by acute bladder overdistension [2][3]
- IVDU — risk of epidural abscess → cord compression [4]
- Sexual history — STDs → urethral stricture; genital herpes → sacral nerve involvement [4]
- Occupation — exposure to arylamines/dyes (bladder CA risk) [7]
- Functional baseline / ADLs — mobility, continence pre-admission, living situation, carers
| Diagnosis | Key Differentiating Question | Expected Finding |
|---|---|---|
| BPH | Long history of progressive obstructive LUTS, nocturia | Most common; older male, gradual worsening |
| CA Prostate | Bony pain (back, hips), weight loss, haematuria | Rapid progression, hard irregular prostate on DRE |
| Urethral stricture | History of previous catheterization, urethral instrumentation, STDs | Young/middle-aged male, very slow stream |
| Drug-induced | New medication started within days/weeks | Temporal relationship; resolves when drug stopped |
| Constipation/faecal impaction | Not opened bowels for days, abdominal distension | Common precipitant in elderly, often overlooked |
| Spinal cord compression | Back pain + leg weakness + sensory level + bowel dysfunction | EMERGENCY — needs urgent MRI |
| Cauda equina syndrome | Saddle anaesthesia, bilateral leg pain, bowel/bladder dysfunction | EMERGENCY — needs urgent MRI and decompression |
| Post-operative | Recent GA/epidural, onset within hours of surgery | Bladder overdistension from reduced detrusor function post-anaesthesia [3][4] |
| Genital herpes | Painful vesicular lesions around genitalia | Sacral nerve involvement [4] |
Red Flags — Escalate Immediately
- Bilateral lower limb weakness + sensory level + back pain → Spinal cord compression — URGENT MRI, call neurosurgery/spinal team
- Saddle anaesthesia + faecal incontinence → Cauda equina syndrome — EMERGENCY surgical decompression
- Fever + rigors + retention → Infected retention / urosepsis — urgent catheterization + IV antibiotics + sepsis protocol
- Raised creatinine + bilateral hydronephrosis → Obstructive nephropathy — needs urgent decompression, monitor for post-obstructive diuresis [4]
- First catheterized volume >1000mL → Likely chronic retention of urine rather than pure AROU, suggesting chronic obstruction with potential renal damage [2][4]
- Blood at urethral meatus / high-riding prostate → Urethral injury — do NOT attempt urethral catheterization; call urology for suprapubic catheter [2]
Pitfalls Students Often Fall Into
- Forgetting to differentiate AROU from anuria — A patient not passing urine ≠ retention. Always check if the bladder is full. If the bladder is empty, think pre-renal or renal causes of oliguria/anuria [2][3].
- Not asking about medications — Drug-induced AROU is a top cause and the most reversible. Students frequently skip this. Go through cold medicines, inhalers, psychiatric meds, and opioids systematically.
- Ignoring constipation — Constipation accounts for 7.5% of AROU in males [2]. Always ask about bowels.
- Failing to screen for neurological red flags — If you miss spinal cord compression, the patient may end up paraplegic. Always ask about back pain, leg weakness, saddle anaesthesia, and bowel dysfunction.
- Ordering PSA in the acute setting — PSA is NOT required during an episode of AROU as it is expected to be elevated (false positive) [4]. PSA should be done 4–6 weeks later [2].
- Assuming normal prostate on DRE excludes BPH — A normal prostate examination does NOT exclude BPH as a cause of obstruction [4]. The median lobe may protrude into the bladder without enlarging the gland externally.
- Not assessing for chronic-on-acute retention — If the patient has been dribbling with a vague sense of fullness for weeks, this is not purely acute. First catheterized volume >1L is the clue [2].
| What You Ask | Why It Matters for the OSCE |
|---|---|
| Painful vs painless | Acute = painful (innervation intact, e.g. BPH); Chronic = painless (innervation abnormal, e.g. DM neuropathy) [1][2] — this is a classic opening viva question |
| First catheterized volume | >500mL = genuine AROU; >1000mL = likely chronic retention [4] |
| IPSS score | Quantifies LUTS severity; mild 0–7, moderate 8–19, severe 20–35 [4][5] — shows you understand grading |
| Drug history | Demonstrates clinical reasoning — if you identify a culprit drug, you can propose stopping it as first-line management |
| Neurological symptoms | Shows you are thinking about dangerous differentials — examiners love this |
| Constitutional symptoms | Demonstrates you are screening for malignancy — a must in any urological history |
| Sexual history / STDs | Links to urethral stricture — shows depth of knowledge |
| Bowel history | Shows you know about constipation as a precipitant — a subtle but important point |
"Mr Chan is a 72-year-old gentleman with a background of hypertension, type 2 diabetes mellitus, and benign prostatic hyperplasia (on tamsulosin), who presented this evening to Queen Mary Hospital with a 6-hour history of inability to pass urine associated with severe suprapubic pain and distension.
In terms of his presenting complaint, he reports progressive lower urinary tract symptoms over the past 2 years, including hesitancy, weak stream, nocturia three times per night, and a sensation of incomplete emptying. His IPSS score is approximately 22 out of 35, indicating severe symptoms. He denies any prior episodes of retention. He denies haematuria, dysuria, fever, or weight loss. There are no neurological symptoms — no back pain, no leg weakness, no saddle anaesthesia, and no change in bowel control. He has been constipated for the past 4 days and has not opened his bowels. He was started on a new cold medication (containing pseudoephedrine) by his GP 3 days ago for an upper respiratory tract infection.
His past medical history includes hypertension, type 2 diabetes mellitus (well controlled, HbA1c 6.8%), BPH diagnosed 3 years ago, and hyperlipidaemia. He has no history of STDs, stroke, malignancy, or neurological disease. He has no previous surgical history.
His regular medications are tamsulosin 0.4mg daily, metformin 500mg BD, amlodipine 5mg daily, and atorvastatin 20mg daily. The new pseudoephedrine-containing cold medication was started 3 days ago. He has no known drug allergies.
His family history is significant for his father being diagnosed with prostate cancer at age 78.
Socially, he is a retired bus driver, lives with his wife, is independently mobile, and manages all activities of daily living. He is a non-smoker and drinks 1–2 beers per week. He denies any illicit drug use.
In summary, this is a case of acute retention of urine in an elderly gentleman with known BPH and severe baseline LUTS, likely precipitated by the combination of constipation and a recently commenced sympathomimetic cold medication. I would like to confirm the diagnosis with a bladder scan, proceed with urethral catheterization for bladder decompression, stop the pseudoephedrine, manage his constipation, check bloods including RFT and CBC, and send catheterized urine for microscopy and culture. PSA should be deferred for 4–6 weeks."
High Yield Summary
AROU = sudden, painful inability to void despite a full bladder. It is the most common urological emergency.
History-taking framework — ask yourself 5 questions in order:
- Is it true AROU? — Confirm full bladder (painful suprapubic distension), rule out anuria/oliguria, differentiate from chronic retention (painless)
- What characterizes this episode? — First vs recurrent, precipitants (surgery, drugs, alcohol, constipation, immobility)
- Is there underlying BOO? — Preceding obstructive LUTS using IPSS; BPH complications (haematuria, UTI, stones, renal impairment)
- Is there a neurological cause? — MUST rule out spinal cord compression (back pain, leg weakness, sensory level, saddle anaesthesia, bowel dysfunction)
- What drugs might be responsible? — Sympathomimetics (cold meds), anticholinergics, antipsychotics, antidepressants, opioids
Critical pearl: Do NOT check PSA during an acute episode — it will be falsely elevated. Defer 4–6 weeks.
Most common cause in males: BPH (53%). In females: detrusor underactivity / neurogenic bladder.
Active Recall - History Taking
[1] Lecture slides: GC 180. Benign prostatic hyperplasia, bladder outlet obstruction and urinary retention.pdf (p23, p24, p30, p33, p37) [2] Senior notes: Ryan Ho Urogenital.pdf (p162–167) [3] Senior notes: Ryan Ho Fundamentals.pdf (p347–352) [4] Senior notes: felixlai.md (Acute retention of urine section, p770–774) [5] Lecture slides: Benign Prostatic Hyperplasia.pdf (p10) [6] Lecture slides: GC 183. Common urological malignancies and their presentations - Nov 7.pdf [7] Senior notes: maxim.md (Urology section, p635–658)
Acute Retention of Urine (AROU)
Acute urinary retention (AUR / AROU) is defined as the sudden inability to pass urine despite having a full bladder [1]. It is a painful condition — the patient is acutely distressed, with a palpable, tense bladder and a desperate urge to void but physically cannot.
Let's break the name down:
- Acute = sudden onset (hours, not weeks)
- Retention = urine is produced but cannot be expelled — the bladder is full
- Of Urine = distinguishing it from bowel/other retention
This is fundamentally different from anuria/oliguria, where the kidneys are simply not producing urine (pre-renal or renal failure). In AROU, the kidneys are working fine — the problem is downstream, at the level of the bladder outlet or detrusor muscle [2][3].
AROU vs CROU vs Anuria – Don't Confuse Them
| AROU | CROU | Anuria/Oliguria | |
|---|---|---|---|
| Onset | Sudden | Gradual | Variable |
| Pain | Painful (innervation intact) | Usually painless (innervation often abnormal) | No suprapubic pain |
| Bladder | Distended, tense | Distended, may be massive | Not distended |
| Mechanism | BOO / acute detrusor failure | Chronic BOO / detrusor underactivity | Failure of urine production |
| Classic cause | BPH (males) | DM neuropathy | Shock, ATN, GN |
Students often confuse AROU with oliguria on the wards. The key distinguishing feature: in AROU, the bladder is full and palpable; in oliguria, the bladder is empty [2][3].
2. Epidemiology
- AROU is the most common urological emergency [1][2][3]
- Common reason for hospital admission in Urology [1]
In Males:
- About 7 per 1,000 men per year [1]
- Overall cumulative probability of AUR in 4 years = 3% [1]
- Over 5 years [1]:
- 10% of men in their 70s will have AUR
- ~30% of men in their 80s will have AUR
- Overwhelmingly more common in men because of the prostate gland — an organ that females simply do not have, and which progressively enlarges with age
In Females:
This is best understood through physiology:
| Feature | Male | Female |
|---|---|---|
| Physiological bladder outlet resistance | Higher (prostate surrounds urethra) | Lower (no prostate, shorter urethra) |
| Voiding depends more on | Detrusor contraction | Pelvic floor relaxation |
| Detrusor contraction strength | Stronger (~60 cmH₂O) | Weaker (~20 cmH₂O) |
| Common AROU mechanism | BOO more common | Detrusor underactivity more common |
Because males have higher outlet resistance (prostate), their detrusor muscle must generate more force to void. This means any additional increase in outlet resistance (e.g., BPH) can tip the balance into retention. Females have low baseline resistance, so obstruction is rarely the issue — instead, their weaker detrusor is more susceptible to underactivity [2].
3. Risk Factors
Rates of AUR found to be increased with:
- Increasing age
- Increasing prostate size
- Increasing BPH symptoms
- Decreasing maximal urine flow rate [1]
These four risk factors reflect the progressive nature of BPH — as the prostate enlarges, symptoms worsen, flow rate drops, and eventually the detrusor can no longer overcome the obstruction.
- Bladder outlet obstruction is less common
- Some may have detrusor underactivity [2]
- Risk factors include: diabetes mellitus (autonomic neuropathy), pelvic organ prolapse, pelvic surgery, neurological disease
These are the "last straw" triggers that push a patient with borderline compensation into overt retention:
| Precipitating Factor | Mechanism |
|---|---|
| Constipation | Faecal impaction in the rectum mechanically compresses the prostatic urethra/bladder neck from posteriorly (constipation is usually not a standalone aetiology but a precipitating factor with background prostatic enlargement) [2] |
| UTI | Pain and inflammation cause reflex urethral sphincter spasm; mucosal oedema further narrows the urethra |
| Anaesthesia or analgesia | GA and epidural/spinal anaesthesia block the sacral parasympathetic outflow (S2-4) → detrusor cannot contract; opioid analgesics also suppress the micturition reflex centrally |
| Immobility | Patients find it difficult to void when supine; prolonged recumbency reduces voiding efficiency |
| Painful perianal conditions | Thrombosed haemorrhoids, perianal abscess → reflex spasm of pelvic floor and urethral sphincter (pain inhibits micturition reflex) |
| Excessive fluid intake (especially alcohol) | Alcohol is a diuretic (suppresses ADH) → rapidly fills the bladder; alcohol also has a sedating/CNS depressant effect → patient may not respond to urge to void → overdistension |
| Drugs | See drug-induced aetiology below |
4. Anatomy and Physiology of Micturition
Understanding AROU requires understanding normal voiding. Think of it as a hydraulic system with a pump (detrusor), two valves (sphincters), and a pipe (urethra), all under neural control.
The lower urinary tract consists of [1][2]:
- Male: bladder, prostate, urethra
- Female: bladder, urethra
Key structures:
- Detrusor muscle: the smooth muscle wall of the bladder; the "pump" that contracts to expel urine
- Proximal sphincter mechanism (PSM): at the bladder neck; composed of smooth muscle; under autonomic control (sympathetic)
- Distal sphincter mechanism (DSM): external urethral sphincter; composed of striated muscle; under somatic (voluntary) control via the pudendal nerve (S2-4)
- Prostate (males): surrounds the prostatic urethra; acts as a secondary continence device but is also the most common site of obstruction in men
Storage phase:
- Accommodation of urine at low pressure with appropriate sensation
- Bladder outlet remains closed at rest or despite increased intra-abdominal pressure
- No involuntary bladder contraction (detrusor overactivity)
Emptying phase:
- Coordinated contraction of bladder smooth muscles at adequate magnitude and duration
- Decreased resistance at bladder outlet
- Proximal sphincter mechanism (PSM) at bladder neck by autonomic control
- Distal sphincter mechanism (DSM) by somatic control
- No anatomical obstruction
Laplace's law: T = P_ves × R / 2d
Where:
- T = wall tension
- P_ves = intravesical pressure
- R = radius of the bladder
- d = wall thickness
To store urine at the same pressure, increasing volume must be accompanied by decreasing tension. This is achieved by receptive relaxation — the ability of the detrusor muscle to accommodate increasing volume without a proportionate rise in pressure.
In pathological conditions (e.g., radiation cystitis, chronic obstruction with fibrosis), the bladder becomes hypocompliant → markedly increased pressure during filling → risk of upper tract damage [1][2].
This is critical to understanding both normal voiding and neurogenic causes of AROU.
- Aδ fibres for signals of distension (normal filling sensation)
- C-fibres for signals of irritation/pain (normally silent; become active in pathological states like infection or neuropathy)
- Travel along hypogastric, pelvic (majority), and pudendal nerves
- Target: higher centres (pontine micturition centre → cerebral cortex)
Efferent pathways — three key nerve supplies:
| Nerve | Origin | Neurotransmitter / Receptor | Target | Function |
|---|---|---|---|---|
| Hypogastric nerve (sympathetic) | T10-L2 | Noradrenaline → α₁ receptors (bladder neck/prostate) and β₃ receptors (detrusor) | Bladder neck smooth muscle, detrusor | Storage: α₁ → contracts bladder neck (↑ outlet resistance); β₃ → relaxes detrusor (↓ tone during filling) |
| Pelvic nerve (parasympathetic) | S2-S4 | Acetylcholine → M₃ muscarinic receptors | Detrusor muscle | Voiding: contracts detrusor |
| Pudendal nerve (somatic) | S2-S4 (Onuf's nucleus) | Acetylcholine → nicotinic receptors | External urethral sphincter (striated muscle) | Voluntary continence: contracts external sphincter; relaxes during voiding |
- Filling: Urine fills bladder → stretch receptors (Aδ fibres) fire → signal travels via pelvic nerve to sacral spinal cord → ascends to pontine micturition centre (PMC) → cortex
- Decision to void: Cortex decides it is socially appropriate → signal sent down to PMC
- Voiding initiation (PMC coordinates):
- Parasympathetic activation (pelvic nerve, S2-4) → ACh at M₃ receptors → detrusor contracts
- Sympathetic inhibition (hypogastric nerve) → α₁ receptors de-activated → bladder neck relaxes
- Somatic inhibition (pudendal nerve) → external sphincter relaxes
- Coordinated voiding: detrusor contracts AND sphincters relax simultaneously → low-pressure urination
Why Understanding Innervation Matters for AROU
Every cause of AROU can be mapped back to a disruption of one of these steps:
- Obstruction = urethra/bladder neck physically blocked (step 4 impossible)
- Sympathomimetics = α₁ stimulation → bladder neck won't relax
- Anticholinergics = M₃ blockade → detrusor won't contract
- Spinal cord lesion = pathway between PMC and sacral cord interrupted → dyssynergia
- Post-GA = sacral parasympathetic output suppressed → no detrusor contraction
Cause: spinal cord injury, pontine stroke
Mechanism: interruption of descending control by pontine micturition centre → Failure of detrusor-sphincter coordination → Synchronous contraction of both detrusor AND sphincters
Consequence: markedly increased urinary tract pressure → upper tract damage
In DSD, the detrusor contracts (sacral reflex arc is intact) but the sphincter also contracts simultaneously (because the PMC, which normally coordinates sphincter relaxation, cannot send its signals down). This creates a functional obstruction with dangerously high pressures — like trying to pump water through a closed valve.
5. Aetiology
The aetiology of AROU can be divided into three major pathophysiological categories: obstruction, detrusor failure, and neurological impairment. In practice, it is often a mixture of factors [2].
Table 2: Aetiology of AUR (Murray et al., 1984) [1]:
| Cause | Percentage |
|---|---|
| Benign prostatic hyperplasia | 53% |
| Constipation | 7.5% |
| Carcinoma of the prostate | 7% |
| Urethral stricture | 3.5% |
| Clot retention | 3% |
| Neurological disorders | 2% |
| Post-operative | 2% |
| Calculus | 2% |
| Drugs | 2% |
| Infection | 2% |
| Miscellaneous/unknown | 16% |
BPH accounts for over half of all AROU cases. This is extremely high-yield.
5.2 Mechanical Bladder Outlet Obstruction (BOO) [1][2][3]
Think of it as: where is the blockage? Extramural (outside the tube), mural (in the wall), or intraluminal (inside the tube)?
| Category | Causes | Pathophysiological Basis |
|---|---|---|
| Extramural | BPH | Transition zone hyperplasia → compresses prostatic urethra from outside. The prostate wraps around the urethra like a doughnut — as it grows, the "hole" gets smaller |
| Cancer of prostate | Malignant infiltration/enlargement of prostate → compresses and invades urethra | |
| Constipation / Faecal impaction | Loaded rectum directly posterior to prostate → mechanical compression of prostatic urethra against pubic symphysis | |
| Pelvic tumours | Mass effect compressing bladder neck/urethra | |
| Prostatitis | Acute inflammation → oedema of prostate → compression of prostatic urethra; also painful voiding reflexly inhibits detrusor | |
| Pregnancy (females) | Gravid uterus compresses bladder neck | |
| Pelvic organ prolapse (females) | Cystocele kinks the urethra; rectocele/uterovaginal prolapse distorts anatomy | |
| Gynaecological tumours (females) | e.g., fibroids compressing bladder neck | |
| Mural | Bladder neck stenosis (usually after previous prostate surgery) | Post-operative scarring/fibrosis at bladder neck → stricture |
| Urethral stricture (iatrogenic or infection/inflammation) | Previous catheterisation, instrumentation, or STDs (especially gonococcal urethritis) → fibrosis → narrowing of urethral lumen | |
| Urethritis | Inflammation → mucosal oedema → narrowing; also painful → reflex sphincter spasm | |
| Bladder tumour | Tumour at bladder neck can physically obstruct the internal urethral orifice | |
| Intraluminal | Bladder/Urethral stone | Stone lodges at bladder neck or urethra → ball-valve obstruction |
| Clot retention (severe gross haematuria) | Blood clots fill the bladder and obstruct the bladder outlet — the bladder becomes full of clot and cannot empty | |
| Foreign bodies | Rare; inserted objects or migrated devices | |
| Phimosis | Tight foreskin → cannot retract → obstructs external urethral meatus. "Phimosis" from Greek phimos = muzzle |
Detrusor underactivity more common:
- Detrusor hypocontractility – exclude DM
- Neurogenic bladder
- Idiopathic
Neurogenic bladder [1]:
- Bladder dysfunction associated with other neurological deficit
- E.g., SCI, CVA, parkinsonism
Other obstructive causes in females: pelvic organ prolapse (cystocele), gynaecological tumours (fibroid) [2]
Drugs are a very common precipitant — always ask about new medications!
| Drug Class | Examples | Mechanism |
|---|---|---|
| Sympathomimetics – α-agonists | Phenylephrine (in cold/cough medications, nasal decongestants), ephedrine, pseudoephedrine | α₁ agonism → contracts smooth muscle at bladder neck and prostatic urethra → ↑ outlet resistance → cannot void |
| Sympathomimetics – β-agonists | Terbutaline, salbutamol (bronchodilators), isoproterenol | β₂/β₃ agonism → relaxes detrusor smooth muscle → bladder cannot generate enough contraction force; also some β₃ effect directly relaxes detrusor |
| Anticholinergics | Atropine, ipratropium (bronchodilators), oxybutynin, tolterodine | Block M₃ muscarinic receptors on detrusor → bladder cannot contract. This is literally the same receptor that parasympathetic nerves use to trigger voiding |
| Antipsychotics | Chlorpromazine, haloperidol, risperidone | Anticholinergic side effects → same as above |
| Antidepressants | TCAs (amitriptyline), SSRIs (less common) | TCAs have strong anticholinergic properties; also α-adrenergic effects |
| Antihistamines | Diphenhydramine, chlorpheniramine | First-generation antihistamines have significant anticholinergic effects |
| Opioids | Morphine, codeine, tramadol | Central suppression of micturition reflex + smooth muscle spasm + anticholinergic-like effects |
| Antispasmodics | Various | Anticholinergic effect |
| Disopyramide | Class Ia antiarrhythmic | Strong anticholinergic side effect |
| MDMA (Ecstasy) | Recreational drug | Sympathomimetic → α₁ agonism at bladder neck |
Exam Pearl: The Cold Medicine Trap
A classic exam scenario: elderly man with known BPH takes an over-the-counter cold remedy containing pseudoephedrine (α-agonist) and chlorpheniramine (antihistamine/anticholinergic) → double hit: ↑ outlet resistance + ↓ detrusor contraction → AROU. Always ask about OTC medications!
| Level of Lesion | Causes | Mechanism |
|---|---|---|
| Brain | Stroke, Parkinson's disease, multiple sclerosis (MS), normal pressure hydrocephalus (NPH), multiple system atrophy (MSA) | Disruption of cortical/subcortical inhibition of micturition reflex. In stroke, may initially get retention (acute "spinal shock"-like phase) before later developing detrusor overactivity |
| Spinal cord | Trauma, vertebral metastasis, spinal stenosis, transverse myelitis, spinal cord haematoma/abscess, spinal cord tumour, epidural abscess, epidural metastasis | Interruption between PMC and sacral micturition centre → DSD (detrusor contracts but sphincter won't relax) OR loss of detrusor contraction in acute phase. Must rule out spinal cord compression — this is a surgical emergency! |
| Peripheral nerves | Diabetic neuropathy, radical pelvic surgery (damage to pelvic plexus), Guillain-Barré syndrome (GBS), genital herpes (sacral nerve involvement) | Damage to pelvic parasympathetic nerves → detrusor cannot contract (areflexic/hypotonic bladder). In DM, insidious autonomic neuropathy → progressive loss of bladder sensation and detrusor tone |
Red Flag: Spinal Cord Compression
In any patient presenting with AROU + new neurological deficits (limb weakness, sensory level, saddle anaesthesia, loss of anal tone), you must urgently rule out spinal cord compression. This requires emergency MRI spine. Delay can lead to permanent paralysis and bladder dysfunction. A neurological exam including assessment of sensory level is mandatory in every AROU patient [3].
This is the mechanism behind post-operative and post-anaesthetic AROU.
Increased urine production:
- Excessive fluid intake (especially alcohol) — alcohol inhibits ADH → massive diuresis; patient may also be sedated and ignore urge to void
Decreased voiding:
- Post-anaesthesia (GA, epidural) — GA depresses the micturition reflex centrally; epidural/spinal blocks the sacral parasympathetic outflow directly → detrusor paralysis
- Analgesics (opioids) — central suppression of voiding reflex
- Painful perianal pathologies — reflex sphincter spasm
- Prolonged immobility — voiding is inefficient when supine; psychologically difficult for many patients to void in bed
Overdistension can stretch detrusor muscles beyond their optimal length of action, leading to ineffective contraction [2]. This is essentially the Frank-Starling mechanism applied to the bladder: if the muscle fibres are stretched beyond the optimal overlap of actin and myosin filaments, contraction force drops dramatically. The bladder becomes a floppy, atonic bag — even after the initial cause is removed, the detrusor may take days to recover.
| Category | Subcategory | Specific Causes |
|---|---|---|
| Mechanical BOO | Extramural | BPH, CA prostate, constipation, pelvic tumours, prostatitis, pregnancy, POP, gynae tumours |
| Mural | Urethral stricture, bladder neck stenosis, urethritis, bladder tumour | |
| Intraluminal | Stones, clot retention, foreign bodies, phimosis | |
| Drug-induced | Sympathomimetics | α-agonists (cold meds), β-agonists (bronchodilators), MDMA |
| Anticholinergics | Atropine, antihistamines, antipsychotics, TCAs, antispasmodics, opioids, disopyramide | |
| Neurological | Brain | Stroke, Parkinson's, MS, NPH, MSA |
| Spinal cord | Trauma, mets, stenosis, myelitis, abscess, tumour | |
| Peripheral | DM neuropathy, radical pelvic surgery, GBS, genital herpes | |
| Acute overdistension | ↑ production | Excessive fluid/alcohol, IV fluids |
| ↓ voiding | Post-GA/epidural, opioids, immobility, perianal pain |
6. Classification
| Feature | Acute (AROU) | Chronic (CROU) |
|---|---|---|
| Onset | Sudden | Gradual (weeks–months) |
| Pain | Painful (intact innervation, rapid distension) | Usually painless (slow distension, often abnormal innervation) |
| Typical cause | BPH | Hypocontractile bladder (e.g., DM neuropathy) |
| Bladder | Tense, tender, palpable | Large, non-tender, may be massive |
| Can lead to | Acute post-renal AKI if untreated | Overflow incontinence, chronic renal impairment |
- Obstructive — physical or dynamic blockage of urine outflow
- Non-obstructive — failure of detrusor contraction (neurogenic, drug-induced, overdistension)
- Mixed — most real-world cases; e.g., elderly man with BPH (partial obstruction) who takes a cold remedy (drug-induced ↓ contraction + ↑ resistance) after drinking alcohol (overdistension)
- Spontaneous: occurs without an identifiable trigger; usually indicates more severe underlying obstruction (e.g., larger prostate → worse prognosis for trial without catheter)
- Precipitated: clear trigger identified (e.g., post-op, drugs, constipation); generally better prognosis as removing the precipitant may allow voiding to resume
7. Pathophysiology — Bringing It All Together
Pathophysiology of Urinary Retention [1] — the lecture specifically dedicates a section to this.
7.1 The Three Mechanisms
The pathogenesis is often a mixture of factors [2]:
Outflow obstruction: may be
- Mechanical (physical narrowing): extramural, mural, luminal
- Dynamic (increased muscle tone), e.g., DSD leading to incomplete relaxation of sphincters
Mechanical obstruction: Physical narrowing of the urethral channel by tissue (BPH, stricture, stone, tumour). The detrusor must generate increasingly higher pressures to overcome the resistance. Eventually, the detrusor cannot generate enough force → retention.
Dynamic obstruction: Increased smooth muscle tone in the prostatic urethra and bladder neck, mediated by α₁-adrenergic receptors. This is the rationale for α₁-blockers (e.g., tamsulosin) in BPH — they reduce dynamic obstruction by relaxing smooth muscle.
In BPH, both components contribute:
Decreased detrusor contraction: may be
- Neurological, e.g., DM neuropathy, stroke, SCI
- Drug-induced, e.g., sympathomimetics, anticholinergics
- Acute overdistension, e.g., post-GA, immobilization
The detrusor is a smooth muscle — it needs intact parasympathetic innervation (S2-4, pelvic nerve, ACh at M₃ receptors) to contract. Anything that interrupts this pathway = retention.
Overdistension is a particularly insidious mechanism: the detrusor is stretched beyond the optimal length-tension relationship for its actin-myosin cross-bridges → contraction force plummets → a vicious cycle where the more distended it gets, the less it can contract [2].
In suprasacral spinal cord lesions, the sacral reflex arc is intact (so the detrusor contracts) but the coordinating signal from the PMC is lost (so the sphincter also contracts simultaneously). High pressures are generated but urine cannot flow — this is particularly dangerous for the upper tracts.
- Immediate: Pain, distress, autonomic dysreflexia (in SCI patients — dangerous hypertension)
- Hours: Bladder overdistension → detrusor damage
- Days: Post-renal AKI — bilateral ureteric obstruction (backpressure) or severe unilateral in single kidney
- Chronic if unrelieved: Hydronephrosis → obstructive uropathy → chronic kidney disease
BPH pathophysiology [3]:
- Obstruction:
- Static component: stromal hyperplasia mediated by dihydrotestosterone (DHT) via 5α-reductase → 5α-reductase inhibitors (5-ARI)
- Dynamic component: smooth muscle hypertrophy and contraction by α₁ receptors → α₁-blockers
- Irritation: detrusor instability causing overactive bladder
- Complications: increased residual urine, causing infection and stone
The progression from BPH to AROU:
- Prostate enlarges (transition zone) → urethral compression
- Detrusor compensates by hypertrophy → initially maintains flow
- Over time, detrusor decompensates → ↑ residual urine → ↑ risk of retention
- Precipitating event (cold, constipation, drugs, alcohol) → tips balance → AROU
Complications of BPH [3]:
- Prostate level: bleeding (ruptured dilated bladder neck veins)
- Bladder level: AROU, recurrent UTI, bladder stone, diverticulum, chronic ROU ± overflow incontinence
- Upper tract: Recurrent hydronephrosis, obstructive uropathy, renal failure
8. Clinical Features
| Symptom | Pathophysiological Basis |
|---|---|
| Acute suprapubic pain | Rapid bladder distension stretches the bladder wall → activates C-fibre nociceptors and Aδ afferents → severe visceral pain. This is the hallmark symptom distinguishing AROU from CROU (where innervation is often impaired, so pain is absent) |
| Inability to void | The defining symptom. Urine is being produced but cannot exit — either because of outlet obstruction or detrusor failure |
| Sensation of fullness / urgency | Stretch receptors in the bladder wall (Aδ fibres) are firing constantly, generating an overwhelming urge to void — but the patient cannot |
| Restlessness and agitation | Severe pain and sympathetic activation from visceral distension |
| Overflow dribbling (may occur) | If intravesical pressure exceeds urethral resistance at any point, small amounts of urine may leak out — patients may paradoxically appear to be passing urine despite retention. Don't be fooled! |
| Previous LUTS (in BPH) | Obstructive LUTS: hesitancy, weak stream, straining, dribbling, incomplete emptying → these suggest pre-existing BOO (especially BPH) that has now decompensated into complete retention [2] |
| Haematuria (in some causes) | Gross haematuria may occur: prostatic venous congestion → ruptured vessels; or bladder tumour; or clot retention causing AROU |
| Fever + dysuria (if associated UTI) | Stagnant urine is a perfect culture medium for bacteria → UTI is both a complication and a precipitant of AROU |
| Uraemic symptoms (if prolonged retention) | Bilateral obstruction → post-renal AKI → nausea, confusion, pruritus, anorexia |
| Strangury (if stone) | Strangury = painful, frequent urination of small volumes, expelled slowly only by straining despite severe urgency and feeling of incomplete emptying [2] — characteristic of bladder/urethral stones |
Is it true AROU? [2]
- Confirm urinary retention → check bladder USG / first catheterised urine volume → rule out oliguria/anuria
- Confirm AROU → ask for painful suprapubic distension → rule out chronic ROU
How is the AROU like? [2]
- Characterise current episode
- First time or recurrent?
- Any precipitating events?: recent surgery, new medications, pelvic trauma, immobilisation, alcohol consumption, genitourinary instrumentations
Is it bladder outlet obstruction? — ask about previous LUTS [2]
- Obstructive LUTS: hesitancy, weak stream, straining, dribbling, incomplete emptying
- IPSS (International Prostate Symptom Score) can be used for male [2]
Is it BPH? — ask about other symptoms/complications of BPH [2]:
- Gross haematuria
- UTI: fever, dysuria
- Bladder/urethral stones: strangury
- Renal impairment: uraemic symptoms
Additional history to elicit:
- Drug history (especially cold remedies, anticholinergics, opioids, bronchodilators)
- Bowel history (constipation)
- Neurological symptoms (limb weakness, numbness, back pain, saddle anaesthesia, loss of anal tone — suggesting spinal cord compression)
- Past surgical history (previous prostate surgery → bladder neck stenosis; previous urethral instrumentation → stricture)
- DM and other medical history (DM neuropathy, Parkinson's, MS)
- Sexual and STI history (gonococcal urethritis → stricture)
| Sign | How to Elicit | Pathophysiological Basis |
|---|---|---|
| Palpable bladder | Suprapubic palpation — a smooth, rounded, tense mass arising from the pelvis; cannot get below it | Bladder palpable when > 200 mL [3]. A full, distended bladder rises above the pubic symphysis and becomes palpable abdominally |
| Suprapubic dullness to percussion | Percuss from umbilicus downward — dull note over distended bladder | Bladder dull on percussion when > 150 mL [3]. Fluid-filled bladder transmits sound differently from surrounding air-filled bowel |
| Suprapubic tenderness | Palpation elicits pain | Acute distension stretching the peritoneum overlying the bladder dome → somatic pain |
| Vital signs | Tachycardia, hypertension (pain response); may have fever if associated UTI/prostatitis | Sympathetic activation from pain; sepsis if infected |
| DRE findings [3] | Prostate size/tenderness, masses, anal tone | Enlarged smooth prostate = BPH; hard nodular prostate = CA prostate; tender boggy prostate = prostatitis; ↓ anal tone = neurological cause (cauda equina); rectal mass = constipation/tumour |
| Neurological examination | Sensory level [3]; assess lower limb power, reflexes, perineal sensation (S2-4), bulbocavernosus reflex, anal tone | A sensory level suggests spinal cord compression; absent perineal sensation suggests cauda equina syndrome; absent bulbocavernosus reflex suggests sacral nerve damage |
| External genitalia | Inspect for phimosis (tight foreskin covering meatus), paraphimosis, meatal stenosis, urethral discharge, blood at meatus | Blood at urethral meatus is a contraindication for urethral catheterisation — suggests urethral trauma. Phimosis can physically obstruct the external meatus |
| Abdominal examination | Check for masses, scars (previous surgery), signs of renal failure | Flank tenderness may suggest hydronephrosis |
Examination Checklist for AROU — Don't Forget!
- Vitals — pain response, sepsis?
- Abdomen — palpable/percussible bladder, tenderness, scars, masses
- DRE — prostate (size, consistency, tenderness, median sulcus), rectal mass, anal tone
- External genitalia — phimosis, blood at meatus, discharge
- Neurological exam — sensory level, lower limb power/reflexes, perineal sensation, anal tone
These are all explicitly mentioned in the lecture slides [1] and senior notes [2][3] and are classic OSCE stations.
Given that BPH accounts for 53% of all AROU cases [1], and Hong Kong has an ageing population, BPH-related AROU is overwhelmingly the most tested scenario.
BPH key points [3]:
- Definition: proliferation of stromal component in transitional zone of prostate
- Prostate starts to increase in size at age 40 — usually becomes symptomatic at ~50 years old
- Typical age: 50–80
- LUTS: both obstructive and irritative symptoms (obstructive >> irritative)
- DRE: smooth enlarged > 3 finger-breadths, non-tender, median sulcus present, anal tone intact
Etiology and risk factors of BPH [4]:
- Age
- Race
- Diet
- Metabolic syndrome
- Genetics (role unclear)
- Growth factors (basic fibroblastic GF, insulin-like GF, etc.)
Investigations for BPH [3]:
- IPSS (International Prostate Symptom Score): quantify LUTS (obstructive + irritative + QoL)
- Voiding diary / Frequency-volume chart: at least 3 days, especially if frequency/nocturia
- Urinalysis, microscopy, C/ST (rule out UTI)
- Uroflowmetry: to confirm obstruction
- Volume voided > 150 mL to be representative
- Peak urine flow rate (Qmax): diagnostic ( < 15 mL/sec), prognostic ( < 10 mL/sec: better outcome after TURP)
- Abnormal strain pattern (multiple peaks)
- Post-void residual volume: < 150 mL
- Bloods: RFT, PSA (rule out CA prostate)
- TRUS: assess size of prostate
When a patient presents with AROU, your thinking should be:
High Yield Summary
- AROU = sudden, painful inability to void despite full bladder — most common urological emergency
- Epidemiology: predominantly males > 60; 7/1000 men/year; 10% in 70s, 30% in 80s over 5 years; very rare in females (~3/100k)
- BPH is the #1 cause (53%) — always the first differential in an elderly male
- Three mechanisms: (a) outflow obstruction (mechanical + dynamic), (b) ↓ detrusor contraction (drugs, neurological, overdistension), (c) DSD
- Drug-induced AROU: α-agonists (cold meds) ↑ outlet resistance; anticholinergics ↓ detrusor contraction — always ask about new medications
- Constipation is usually a precipitating factor, not standalone cause — mechanical compression of prostatic urethra
- Acute overdistension damages detrusor by stretching beyond optimal actin-myosin overlap → vicious cycle
- Key exam signs: palpable bladder ( > 200 mL), dull to percussion ( > 150 mL), DRE for prostate, neurological exam for sensory level and anal tone
- Must rule out spinal cord compression in any AROU with neurological deficits — emergency MRI
- AROU ≠ anuria — in AROU the bladder is full; in anuria the bladder is empty
- Distinguish AROU (painful) from CROU (painless) — innervation status determines this
- BPH pathophysiology: static component (DHT/5α-reductase → physical enlargement) + dynamic component (α₁ receptors → smooth muscle tone) → rationale for 5-ARI + α-blockers
Active Recall - Acute Retention of Urine
[1] Lecture slides: GC 180. Benign prostatic hyperplasia, bladder outlet obstruction and urinary retention.pdf (pp. 3, 22–33, 62) [2] Senior notes: Ryan Ho Urogenital.pdf (pp. 159, 162–165); Ryan Ho Fundamentals.pdf (pp. 347–350) [3] Senior notes: maxim.md (sections on AROU and BPH); felixlai.md (AROU section) [4] Lecture slides: Benign Prostatic Hyperplasia.pdf (p. 5) [5] Senior notes: Ryan Ho Critical Care.pdf (p. 25 — post-renal AKI)
Differential Diagnosis of Acute Retention of Urine
The differential diagnosis of AROU is really about answering two sequential questions:
- Does this patient truly have urinary retention? — or is the problem actually that urine is not being produced (anuria/oliguria)?
- If it is retention, what is the underlying cause? — obstruction, detrusor failure, neurological, drug-induced, or a combination?
This sounds simple, but in practice a distressed, oliguric elderly patient on a surgical ward can easily be mislabelled as "not passing urine" when they are actually in pre-renal AKI from dehydration, or conversely, a patient with overflow dribbling may be assumed to be voiding normally when in fact they have a massively distended bladder. The first branch in your differential thinking is therefore the most critical.
AROU should be distinguished from anuria or oliguria → lack of urine production, not retention [2].
| Feature | AROU | Anuria / Oliguria |
|---|---|---|
| Bladder | Full, distended, palpable, tender | Empty, not palpable |
| Pain | Suprapubic pain and urgency | No suprapubic distension |
| Bladder scan | ≥ 300 mL [2] | Minimal volume |
| Urine output | Patient feels urge but cannot void; may have overflow dribbling | Genuinely reduced or absent urine output |
| Pathophysiology | Outflow problem or detrusor failure (urine is produced but trapped) | Production problem (kidneys not making urine) |
Causes of anuria/oliguria to rule out [2][3]:
- Pre-renal ARF due to dehydration and shock — hypovolaemia (haemorrhage, vomiting, diarrhoea, burns, sepsis, cardiogenic shock) → ↓ renal perfusion → ↓ GFR → ↓ urine output [5]
- Renal ARF due to acute tubular necrosis, interstitial nephritis, glomerulonephritis — intrinsic renal damage → kidneys cannot filter [5]
- Post-renal obstruction at the ureteric level — bilateral ureteric stones, retroperitoneal fibrosis, bilateral ureteric tumours → urine cannot reach the bladder at all; bladder will be empty on scan
The bedside bladder scan is your instant differentiator: a full bladder ( ≥ 300 mL) = retention; an empty bladder = look upstream (kidneys, ureters) or systemically (shock, dehydration).
Classic Exam Trap
A post-operative patient has not passed urine for 8 hours. The surgical team assumes "AROU from anaesthesia" and calls for catheterisation. But the bladder scan shows only 50 mL. This is NOT retention — this is oliguria, likely pre-renal AKI from intra-operative blood loss or inadequate fluid resuscitation. Catheterising this patient will not help; they need volume resuscitation and assessment of renal function. Always scan the bladder before assuming retention.
The differential for anuria/oliguria masquerading as AROU [3][5]:
| Cause | Mechanism | Key Clue |
|---|---|---|
| Hypovolaemic shock (e.g., ruptured AAA, GI bleed, trauma) | ↓ circulating volume → ↓ renal perfusion → ↓ GFR → oliguria | Hypotension, tachycardia, empty bladder, history of bleeding/trauma |
| Dehydration (vomiting, diarrhoea, poor intake) | Same as above — pre-renal mechanism | Dry mucous membranes, ↑ urea:creatinine ratio, concentrated urine |
| Septic shock | Distributive shock → ↓ effective circulating volume → pre-renal AKI | Fever, hypotension, source of infection |
| Cardiogenic shock | Pump failure → ↓ cardiac output → ↓ renal perfusion | Raised JVP, pulmonary oedema, hypotension |
| Acute tubular necrosis (ATN) | Ischaemic or nephrotoxic insult → tubular cell death → intrinsic renal failure | Follows prolonged hypotension or nephrotoxin exposure; muddy brown casts on urinalysis |
| Bilateral ureteric obstruction | Stones, tumour, retroperitoneal fibrosis → urine cannot reach bladder | Empty bladder; bilateral hydronephrosis on ultrasound |
Once you have confirmed urinary retention (full bladder), you must determine whether this is acute or chronic [1]:
| Feature | AROU | CROU |
|---|---|---|
| Onset | Sudden | Gradual (weeks to months) |
| Pain | Painful | Usually painless, vague lower abdominal distension |
| Typical cause | Benign prostatic obstruction | Hypocontractile bladder (e.g., DM neuropathy) |
| Bladder volume | Typically 300–800 mL | Can be ≥ 1 L [2] (sometimes > 2 L) |
| Innervation | Usually intact (that is why it hurts) | Often impaired (autonomic neuropathy → loss of bladder sensation → painless) |
| Overflow incontinence | Uncommon (too acute) | Common — constant dribbling, especially at night |
Why does AROU hurt but CROU doesn't? Because in AROU the sensory nerves (Aδ and C-fibres) are intact and firing intensely as the bladder rapidly distends. In CROU, the underlying cause often involves progressive neuropathy (e.g., diabetes) — the nerves that should signal pain are themselves damaged, so the bladder fills silently to enormous volumes.
Bladder Scan Volume Rule of Thumb
3. Differential Diagnosis of AROU by Cause — Organised by Mechanism
This is the core differential diagnosis table. Think of it as answering: "Why can't this patient void?"
These are by far the most common causes in males. Organised by anatomical location (extraluminal → intramural → intraluminal):
| Location | Cause | Why It Causes AROU | Key Differentiating Feature |
|---|---|---|---|
| Extraluminal | BPH | Transition zone hyperplasia compresses prostatic urethra; 53% of all AROU [1] | Age 50–80; DRE: smooth enlarged > 3FB, non-tender, median sulcus present [4]; longstanding obstructive LUTS |
| Cancer of prostate | Malignant infiltration/enlargement → urethral compression; 7% of AROU [1] | DRE: hard, nodular, irregular, median sulcus obliterated; may have bone pain (mets), weight loss, ↑ PSA | |
| Constipation / faecal impaction | Loaded rectum compresses prostatic urethra from posteriorly; 7.5% [1] | Often a precipitating factor with background BPH rather than standalone cause [2]; palpable faecal loading on DRE/AXR | |
| Pelvic tumours | Mass effect compressing bladder neck | History of malignancy; palpable pelvic mass on bimanual/DRE | |
| Prostatitis | Acute prostatic oedema → urethral compression; also pain inhibits voiding reflex | Fever, tender boggy prostate on DRE, dysuria, pyuria; younger patient (20–50) | |
| Pelvic organ prolapse (females) | Cystocele kinks urethra; rectocele/uterovaginal prolapse distorts anatomy | Sensation of vaginal bulge, worsens with standing; visible on pelvic exam | |
| Gynaecological tumours (females) | e.g., large fibroid compresses bladder neck/urethra | Palpable pelvic mass; menorrhagia history | |
| Pregnancy (females) | Gravid uterus compresses bladder outlet, especially retroverted uterus in 1st trimester | Positive pregnancy test; usually self-resolves as uterus rises out of pelvis | |
| Intramural | Bladder neck stenosis | Usually after previous prostate surgery [1]; scarring narrows bladder neck | History of TURP, radical prostatectomy, or radiotherapy |
| Urethral stricture | Iatrogenic or infection/inflammation [1]; fibrosis → luminal narrowing; 3.5% [1] | History of catheterisation, urethral instrumentation, gonococcal urethritis; thin stream/spraying | |
| Urethritis | Mucosal oedema narrows lumen; pain causes reflex sphincter spasm | Urethral discharge, dysuria; history of STI | |
| Bladder tumour | Tumour at bladder neck physically occludes internal urethral orifice [1] | Painless haematuria; risk factors: smoking, occupational dye exposure | |
| Intraluminal | Bladder/urethral stone | Stone lodges at bladder neck or along urethra → ball-valve obstruction; 2% [1] | Strangury (painful straining to void small volumes); haematuria; history of urolithiasis |
| Clot retention (severe gross haematuria) | Blood clots fill bladder and plug outlet; 3% [1] | Obvious gross haematuria preceding retention; causes include bleeding BPH, bladder tumour, post-TURP | |
| Foreign body | Object inserted or migrated into urethra/bladder | Psychiatric history; embarrassed to disclose; visible on imaging | |
| Phimosis | Tight foreskin occludes external urethral meatus [1] | Visible on inspection; cannot retract foreskin; history of recurrent balanitis |
| Drug Class | Examples | Mechanism | Differentiating Clue |
|---|---|---|---|
| Sympathomimetics (α-agonists) | Phenylephrine, ephedrine (cough mixture) [4] | α₁ stimulation → contracts bladder neck/prostatic smooth muscle → ↑ outlet resistance | Recent cold/flu; started OTC cold remedy |
| Sympathomimetics (β-agonists) | Terbutaline, salbutamol | β₂/β₃ agonism → relaxes detrusor → ↓ contractile force | Recent asthma exacerbation with nebuliser use |
| Anticholinergics | Atropine [4], oxybutynin, ipratropium | Block M₃ muscarinic receptors → detrusor cannot contract | New anticholinergic medication; dry mouth, constipation, blurred vision (systemic anticholinergic features) |
| Antipsychotics | Chlorpromazine, olanzapine | Anticholinergic side effect | Psychiatric medication history |
| Antidepressants | TCAs (amitriptyline), SSRIs | TCAs: strong anticholinergic + α-adrenergic effects | Recent initiation or dose increase |
| Antihistamines | Diphenhydramine, chlorpheniramine | 1st-generation: significant anticholinergic effect | OTC allergy/sleep medication |
| Opioids | Morphine, codeine, tramadol | Central suppression of micturition reflex + smooth muscle effects | Post-operative setting [1]; recent analgesia |
| MDMA (Ecstasy) | Recreational | Sympathomimetic → α₁ agonism at bladder neck | Young patient, recreational drug use history |
| Level | Cause | Why It Causes AROU | Differentiating Features |
|---|---|---|---|
| Brain | Stroke, Parkinson's disease, MS, NPH, MSA | Disruption of cortical/subcortical micturition control; acute stroke can cause initial retention before later developing overactivity | Focal neurological deficits; tremor/rigidity (PD); gait ataxia + dementia + incontinence (NPH triad) |
| Spinal cord | SCI, vertebral metastasis, spinal stenosis, transverse myelitis, epidural abscess/metastasis | Interruption of descending pathways from PMC → DSD or loss of detrusor reflex | Sensory level on exam; back pain; lower limb weakness; ↓ anal tone; must rule out spinal cord compression [4] |
| Peripheral nerves | DM neuropathy, radical pelvic surgery, GBS, genital herpes (sacral nerves) | Damage to pelvic parasympathetic efferents → areflexic detrusor | DM history (exclude DM in females with hypocontractility) [1]; ascending weakness (GBS); vesicular rash in S2-4 dermatome (herpes) |
| Cause | Why It Causes AROU | Differentiating Features |
|---|---|---|
| Post-operative / post-anaesthesia | GA/epidural/spinal → blocks sacral parasympathetic outflow; + IV fluids → rapid filling; + opioid analgesia → central suppression of voiding reflex; 2% [1] | Recent surgery/anaesthesia; no prior voiding symptoms |
| Prolonged immobility | Poor voiding efficiency in supine position; psychological difficulty voiding in bed | Hospitalised, bed-bound patient |
| Excessive alcohol intake | Diuresis (ADH suppression) + sedation (ignores urge) → overdistension | Binge drinking history; acute presentation |
| Painful perianal conditions | Thrombosed haemorrhoids, perianal abscess → reflex sphincter spasm from pain | Perianal tenderness; visible pathology on inspection |
4. Sex-Specific Differential Diagnosis Framework
Because the differential is so different between males and females, it is worth having a sex-specific mental framework:
Common obstructive causes in males [1]:
- Benign Prostatic Hyperplasia (BPH)
- Cancer of prostate
- Bladder/Urethral stone
- Bladder neck stenosis (usually after previous prostate surgery)
- Urethral stricture (iatrogenic or infection/inflammation)
- Phimosis
- Bladder tumour
- Clot retention (Severe gross haematuria)
Then consider precipitants: drugs, constipation, alcohol, immobility, post-operative.
Common causes in females [1]:
- Detrusor hypocontractility — exclude DM
- Neurogenic bladder
- Idiopathic
Neurogenic bladder [1]:
- Bladder dysfunction associated with other neurological deficit
- E.g., SCI, CVA, parkinsonism
Then consider obstructive causes (less common): pelvic organ prolapse, gynaecological tumours, pregnancy.
6. How to Differentiate at the Bedside — A Practical Approach
When faced with AROU in the emergency department, here is how you systematically narrow the differential:
- Bladder scan or abdominal palpation/percussion → bladder palpable > 200 mL, dull to percussion > 150 mL [4]
- If bladder empty → not retention → investigate for anuria/oliguria
- Ask about pain (AROU is painful; CROU is painless)
- Ask about duration and previous episodes
- Catheterised volume: ≥ 1 L suggests CROU [2]
| Assessment | What You're Looking For | Differential Narrowed |
|---|---|---|
| Drug history | New cold meds, anticholinergics, opioids, antipsychotics, bronchodilators | Drug-induced |
| Surgical history | Recent surgery/GA, previous prostate surgery, urethral instrumentation | Post-operative retention, bladder neck stenosis, urethral stricture |
| LUTS history | Longstanding hesitancy, weak stream, nocturia (IPSS) | BPH (if obstructive predominant) |
| DRE | Smooth enlarged = BPH; hard nodular = CA prostate; tender boggy = prostatitis; faecal loading = constipation; ↓ anal tone = neurological | Narrows obstructive cause + screens for neurological |
| External genitalia | Phimosis visible; blood at meatus = urethral injury; discharge = urethritis/STI | Phimosis, urethral trauma, urethritis |
| Neurological exam | Sensory level, lower limb weakness, absent perineal sensation, ↓ bulbocavernosus reflex | Spinal cord compression, cauda equina, DM neuropathy |
| Constitutional symptoms | Weight loss, bone pain, anorexia | Malignancy (CA prostate, bladder CA, pelvic tumour) |
| Haematuria | Preceding gross haematuria with clots | Clot retention; underlying cause = bladder tumour, bleeding BPH |
| Pelvic exam (females) | Prolapse, pelvic mass | POP, gynaecological tumour |
| Red Flag | Concern | Action |
|---|---|---|
| New neurological deficit (sensory level, weakness, ↓ anal tone) | Spinal cord compression / cauda equina | Emergency MRI spine |
| Fever + tender prostate | Acute prostatitis / prostatic abscess | Avoid aggressive DRE; antibiotics; avoid catheterisation if possible (suprapubic catheter preferred) |
| Blood at urethral meatus / high-riding prostate | Urethral trauma (e.g., pelvic fracture) | Contraindication for urethral catheterisation → suprapubic catheter or retrograde urethrogram first |
| Grossly elevated creatinine | Obstructive nephropathy / post-renal AKI | Urgent decompression + nephrology input |
| Fever + rigors + retention | Urosepsis | Urgent catheterisation + blood cultures + empirical IV antibiotics |
AROU does not occur in isolation. Most patients presenting with AROU have a background of LUTS. Understanding the differential of LUTS helps you understand what the underlying disease is:
Bladder outlet obstruction typically presents with predominantly voiding symptoms [3]:
- Bladder causes: bladder stones, bladder cancer, bladder neck contracture (scarring from surgery/radiotherapy), interstitial cystitis, ketamine cystitis
- Prostate causes: BPH, prostatic cancer
- Urethral causes: urethral stricture (urinary instrumentation)
Overactive bladder (detrusor overactivity) typically presents with predominantly storage symptoms [3]:
- Neurogenic: stroke, SCI, MS, Parkinson's disease
- Non-neurogenic (idiopathic): post-operative pelvic surgery; secondary to BOO itself (overactive bladder can be secondary to bladder outlet obstruction — the detrusor hypertrophies to overcome obstruction and becomes unstable)
Interestingly, retention of urine appears in the differential diagnosis of delirium [6]:
Drugs, Electrolytes/Ears/Eyes, Low oxygen, Infection, Retention of urine or faeces, Ictogenic, Underhydration/Undernutrition, Metabolic
This reminds us that AROU itself can cause delirium in elderly patients — the pain, discomfort, and autonomic disturbance from a grossly distended bladder can precipitate an acute confusional state. Always check for urinary retention in a delirious patient, and always consider delirium in a patient with retention who becomes confused.
High Yield Summary
- First differentiate AROU from anuria/oliguria — bladder scan is the key: full bladder = retention; empty bladder = production problem (pre-renal/renal/bilateral ureteric obstruction)
- Then differentiate AROU from CROU — AROU is painful (intact innervation, rapid distension); CROU is painless (impaired innervation, gradual distension); ≥ 1 L on catheterisation suggests CROU
- In males, think obstruction first — BPH is #1 (53%) → then CA prostate, constipation, stricture, clot retention, stone, phimosis, bladder tumour, bladder neck stenosis
- In females, think detrusor failure first — detrusor hypocontractility (exclude DM), neurogenic bladder, idiopathic
- Always consider precipitants — drugs (cold meds, anticholinergics, opioids), constipation, post-GA, alcohol, immobility, perianal pain
- Neurological red flags mandate emergency MRI — sensory level, lower limb weakness, loss of anal tone → spinal cord compression until proven otherwise
- Blood at meatus / high-riding prostate → urethral trauma → contraindication for urethral catheterisation
- DRE is the single most important bedside differentiating examination — smooth enlarged = BPH; hard nodular = CA prostate; tender boggy = prostatitis; faecal loading = constipation; ↓ anal tone = neurological
- Do NOT check PSA during AROU — it will be falsely elevated; defer 4–6 weeks [2]
- AROU can cause delirium in elderly — and delirium workup should include checking for retention
Active Recall - Differential Diagnosis of AROU
References
[1] Lecture slides: GC 180. Benign prostatic hyperplasia, bladder outlet obstruction and urinary retention.pdf (pp. 23, 24, 25, 27, 30, 31, 33) [2] Senior notes: Ryan Ho Urogenital.pdf (pp. 164–167); Ryan Ho Fundamentals.pdf (pp. 349–352) [3] Senior notes: felixlai.md (AROU section, differential diagnosis of LUTS section) [4] Senior notes: maxim.md (AROU section, BPH section) [5] Senior notes: Ryan Ho Critical Care.pdf (p. 25 — AKI aetiology) [6] Senior notes: Ryan Ho Psychiatry.pdf (p. 74 — DELIRIUM mnemonic)
Diagnostic Criteria, Diagnostic Algorithm, and Investigation Modalities
AROU does not have formal "diagnostic criteria" in the way that, say, rheumatoid arthritis or heart failure do. Instead, it is a clinical diagnosis confirmed by a simple objective measurement. The diagnosis rests on three pillars:
| Pillar | How to Confirm | Rationale |
|---|---|---|
| 1. Inability to void | Patient reports inability to pass urine despite urge | The defining symptom — urine is trapped |
| 2. Full bladder | Bladder scan ≥ 300 mL in a patient unable to void suggests urinary retention [2] | Confirms that the bladder is full (urine produced but not expelled) rather than empty (anuria/oliguria). This is THE key differentiator |
| 3. Acute and painful | Sudden onset + painful suprapubic distension | Distinguishes from CROU (painless, gradual, ≥ 1 L suggests chronic retention) [2] |
So in practical terms:
AROU is diagnosed when: a patient presents with sudden painful inability to void AND the bladder is confirmed to be distended (bladder scan ≥ 300 mL, or palpable/percussible suprapubic mass, or first catheterised volume ≥ 300 mL).
Can You Skip the Bladder Scan?
Can proceed to catheterisation directly if history and physical examination strongly suggest a diagnosis of AROU [3]. In practice, if you have a distressed elderly man who cannot void, has a palpable tender suprapubic mass, and has known BPH, you do not need to wait for a bladder scan — go ahead and catheterise. But in ambiguous cases (post-operative patient, uncertain history, no palpable bladder), a quick bedside bladder scan takes 30 seconds and can save you from an unnecessary catheterisation in an anuric patient.
2. The Diagnostic Algorithm — Step by Step
The approach to diagnosing and working up AROU happens in two phases: the acute phase (confirm diagnosis + immediate decompression) and the subsequent workup (identify the underlying cause).
3. Investigation Modalities — Comprehensive Breakdown
Investigations in AROU serve two purposes: (A) confirm the diagnosis and (B) identify the underlying cause and assess for complications. Let's go through each modality systematically.
3.1 Bedside Investigations
- What it does: Non-invasive estimation of bladder volume using portable ultrasound
- Why it matters: This is your first-line diagnostic tool — it instantly distinguishes retention (full bladder) from anuria (empty bladder)
- ≥ 300 mL in a patient unable to void suggests urinary retention; ≥ 1 L suggests chronic retention of urine [2]
- Interpretation: If the bladder is distended (≥ 300 mL) and the patient is in pain and cannot void → AROU confirmed
- Caveat: You can skip this if the clinical picture is unambiguous (palpable tender bladder + cannot void) → proceed directly to catheterisation [3]
- What it does: The volume of urine drained on initial catheterisation serves as both a diagnostic and therapeutic measure
- Why it matters: Confirms the diagnosis objectively; the volume gives you a clue about acuity:
- 300–800 mL → typical AROU
- ≥ 1 L → think CROU [2] (or acute-on-chronic)
- Also: send the catheterised urine sample for analysis (see below)
- When: Should be done in both men and women [3]
- What you are assessing:
| Finding | Interpretation |
|---|---|
| Prostate: smooth, symmetrically enlarged > 3FB, no nodules, intact median groove, firm consistency [7] | BPH |
| Hard, nodular, irregular, median sulcus obliterated | CA prostate |
| Tender, boggy, warm | Acute prostatitis |
| Faecal impaction / loaded rectum | Constipation as precipitant |
| Anal sphincter tone + perineal sensation | Neurological integrity; ↓ tone suggests cauda equina / sacral nerve pathology [3][7] |
| Pelvic mass | Rectal/pelvic tumour |
- Precautions [3]:
- Normal prostate examination does NOT exclude BPH as a cause of obstruction — BPH primarily involves the transition zone which is internal; DRE mainly palpates the posterior peripheral zone. A prostate can feel "normal" on DRE yet have significant transition zone enlargement compressing the urethra
- BPH does NOT necessarily cause outflow obstruction — prostate size alone does not predict symptoms; it is the relationship between prostate, urethra, and detrusor function that matters
- Mandatory in every patient with AROU [4]
- Assess: sensory level [4], lower limb muscle tone, power, reflexes, perineal sensation (S2-4 dermatomes), bulbocavernosus reflex, anal tone
- Why: To rule out spinal cord compression / cauda equina syndrome, which is a neurosurgical emergency. If a sensory level or new neurological deficit is found → emergency MRI spine
Investigations after catheterisation [2]:
| Test | What You Are Looking For | Why / Interpretation |
|---|---|---|
| CBC [2][4][8] | Leukocytosis | Suggests UTI, prostatitis, or urosepsis as a precipitant or complication. Anaemia may indicate chronic disease/malignancy |
| Clotting profile [8] | Coagulopathy | To prepare for surgery [8] if intervention is anticipated; also relevant if considering suprapubic catheterisation |
| RFT (Renal Function Test) [2][3][4][8] | Elevated creatinine, elevated urea, hyperkalaemia | Obstructive uropathy / obstructive nephropathy [2][8] — back-pressure from retention → bilateral hydronephrosis → post-renal AKI. A rising creatinine mandates urgent decompression and renal imaging. High serum creatinine can result from bladder outlet obstruction or underlying renal disease — should prompt USG [3] |
| LFT [2] | Baseline | General workup; hepatorenal involvement in chronic disease |
| PSA | DO NOT CHECK | Do NOT take PSA → AROU can cause false elevation (to be done 4–6 weeks later) [2][8]. Why? Prostatic distension and inflammation during AROU cause prostate cells to release PSA into the bloodstream artefactually. PSA: only for patients with life expectancy > 10 years and after detailed counselling. DO NOT CHECK PSA during retention or UTI [8]. The half-life of PSA is 2–3 days [3], so it takes weeks to normalise after the acute event |
PSA Trap — Extremely High Yield
Do NOT check PSA during an episode of AROU [2][8]. This is a classic exam mistake. AROU causes false elevation of PSA due to prostatic distension and ischaemia. Checking it will give a misleadingly high value, causing unnecessary patient anxiety and potentially triggering invasive investigations (biopsy) for a falsely elevated result. Defer PSA measurement to 4–6 weeks after the acute episode [2].
Causes of elevated PSA [3]:
- Prostatitis
- BPH
- Prostate cancer
- Prostate biopsy
- AROU (artefactual)
- DRE (transiently, minimally)
PSA is prostate-specific but NOT prostate-cancer-specific [3].
Catheterised urine: biochemistry, microscopy, C/ST [2][4]
| Test | What You Are Looking For | Why / Interpretation |
|---|---|---|
| Urinalysis (dipstick) [3][4] | Blood, WBCs, nitrites, protein, glucose | Quick screen for haematuria (stone, tumour, infection), pyuria (UTI), glycosuria (undiagnosed DM — relevant as DM neuropathy is a cause of detrusor underactivity) |
| Urine microscopy [3][4] | WBC/HPF, RBC/HPF, casts, crystals, organisms | Detect presence of blood, bacteria and WBC [3]. Pyuria ( > 5 WBC/HPF) with significant bacteriuria → UTI as precipitant. RBC morphology can hint at glomerular vs non-glomerular source |
| Urine C/ST (culture and sensitivity) [3][4] | Organisms and antibiotic sensitivities | Confirms UTI; guides antibiotic choice. Critical because UTI can be both a precipitant and complication of AROU |
| Urine cytology [3] | Malignant cells | Indicated if bladder cancer is suspected in patients presenting with haematuria and predominantly irritative symptoms [3]. Sensitivity ~50%; highest for high-grade transitional cell carcinoma and carcinoma in situ; low detection rate for low-grade cancer |
3.4 Radiological Investigations
- KUB for stones or faecal loading [2][8]
- What it shows: Radio-opaque calculi (calcium oxalate, calcium phosphate stones are visible; uric acid stones are radiolucent and will be missed), faecal loading in the rectosigmoid
- Why: Identifies urolithiasis as a cause of obstruction; confirms constipation/faecal impaction as a precipitant
- Limitations: Cannot detect radiolucent stones, soft tissue masses, or upper tract obstruction
USG bladder (confirm diagnosis) + USG kidney/ureter (hydronephrosis/hydroureter) [4]
| Component | What It Shows | Why It Matters |
|---|---|---|
| USG bladder | Bladder volume, wall thickness, intravesical masses, stones, post-void residual | Confirms retention; thick bladder wall (detrusor hypertrophy) suggests chronic obstruction; intravesical mass suggests tumour or large median lobe of prostate |
| USG kidney/ureter | Hydronephrosis, hydroureter, renal cortical thinning, renal/ureteric stones | Upper tract imaging indicated if large residual volume, haematuria, or history of stone [7]. Hydronephrosis = back-pressure from obstruction → risk of obstructive nephropathy. Cortical thinning suggests chronic damage |
- When: If stone disease is suspected and KUB is inconclusive
- What it shows: Gold standard for detecting urinary stones (including radiolucent uric acid stones); also shows pelvic masses
- Not first-line in straightforward AROU but important if stone is the suspected cause
- IV non-ionic contrast injected → excreted by kidneys → opacifies and visualises urinary system [9]
- Common indications: haematuria, loin pain
- Post-micturition film can detect urinary retention [9]
- Largely superseded by CT urogram in modern practice, but still used in some centres
- Contraindications: pregnancy (radiation), previous serious contrast reactions, diabetes with renal insufficiency (risk of contrast-induced AKI) [9]
- When: Urgently indicated if neurological red flags are present (new sensory level, lower limb weakness, saddle anaesthesia, ↓ anal tone)
- What it shows: Spinal cord compression (disc, tumour, abscess, haematoma), cauda equina syndrome
- Why urgent: Delay in decompression → permanent neurological damage and bladder dysfunction
TRUS [8]:
- Before starting 5α-reductase inhibitors for prostate > 30–40cc
- Before surgery to decide modality of surgical intervention
- Measures prostate volume accurately; detects intravesical prostatic protrusion (IPP) which predicts treatment response
- Not done in the acute phase — this is part of the subsequent elective workup
3.5 Specialised / Elective Investigations (After Acute Phase)
These are performed once the acute episode has resolved and the catheter has been managed, to determine the underlying cause and guide definitive treatment.
- Use: quantify severity of LUTS, predict treatment response, guide treatment decision and monitor response to treatment (NOT a diagnostic tool) [7]
- Involves [7]:
- Voiding symptoms: incomplete emptying, intermittency, weak stream, straining
- Storage symptoms: frequency, urgency, nocturia
- Quality of life measure
- Interpretation: mild (1–7), moderate (8–19), severe (20–35) [7]
- IPSS and QoL scores: assess severity (guide treatment); risk factor for progression [8]
- When to use: After the acute episode; helps quantify baseline LUTS severity and guides whether patient needs watchful waiting, medical therapy, or surgery
- Record time and volume of each void + fluid intake for at least 3 days [4]
- Especially useful if frequency/nocturia are prominent features
- Helps differentiate nocturnal polyuria (large volume, few voids) from overactive bladder (small volumes, many voids)
Uroflowmetry: non-invasive investigation of maximal flow, voided volume, and residual volume [3]
| Parameter | Normal | Abnormal | Interpretation |
|---|---|---|---|
| Voided volume | > 150 mL to be representative [7] | < 150 mL | Invalid test if volume too low |
| Peak flow rate (Qmax) | > 15 mL/s (male); > 30 mL/s (female) [7] | < 10 mL/s | < 10 mL/s: 90% obstructed; 10–15 mL/s: 60% obstructed; > 15 mL/s: only 30% obstructed [8] |
| Flow pattern | Bell-shaped curve | ↓ peak (BPH) vs plateaued (urethral stricture) [7] | Plateaued = fixed narrowing (stricture); ↓ peak = compressive obstruction (BPH) or detrusor underactivity |
| Post-void residual (PVR) | < 50 mL (normal); up to 100–200 mL acceptable in elderly [7] | > 200 mL | Suggests either BOO or detrusor underactivity; large PVR → risk of UTI, stones, upper tract damage |
- Normal maximal flow rate does NOT exclude outflow obstruction — 18% of patients with BOO have Qmax > 15 mL/s [7]
- Uroflowmetry is NOT sufficient to diagnose outflow obstruction since it cannot distinguish between outflow obstruction and poor detrusor contractility [3] — both give ↓ Qmax. To distinguish them, you need urodynamics
Urodynamics: gold-standard for diagnosis of BOO [7]
Investigation of [3]:
- Uroflow rate
- Bladder volume
- Intravesical and rectal pressure (to calculate detrusor pressure = P_ves − P_abd)
- Sphincter function (EMG)
Outflow obstruction is characterised by high pressure, low flow [3]
| Pattern | Detrusor Pressure | Flow Rate | Diagnosis |
|---|---|---|---|
| High pressure, low flow | ↑↑ (detrusor working hard) | ↓↓ | BOO — detrusor is trying to push through an obstruction |
| Low pressure, low flow | ↓ | ↓↓ | Detrusor underactivity (DUA) — the problem is not obstruction but a weak pump |
| Normal pressure, normal flow | Normal | Normal | No BOO, no DUA (consider other causes of symptoms) |
Why does this matter? Because the treatment is completely different. BOO → relieve obstruction (α-blockers, 5-ARI, TURP). DUA → improve detrusor function (cholinergics, intermittent self-catheterisation). If you do TURP on a patient with DUA, you will not fix anything — the obstruction was never the problem.
Indications for urodynamics [8]:
- Atypical age for BPH
- Suspected neurogenic bladder
- History of spinal/pelvic surgery
- Failed intervention (e.g., persistent symptoms after TURP)
- Uncertain diagnosis where uroflowmetry alone cannot distinguish BOO from DUA
Flexible cystoscopy [8]:
- Indications: Haematuria [8] (to rule out bladder tumour), suspected urethral stricture, bladder stones, bladder cancer
- What it shows: Direct visualisation of urethra, prostate (median lobe protrusion), bladder mucosa (tumours, trabeculation from chronic obstruction, diverticula, stones)
- Bladder trabeculation = thickened detrusor muscle bundles visible as ridges — indicates chronic BOO with compensatory hypertrophy
USG / CT urogram: haematuria [8]
- Indicated when haematuria is present — to evaluate the entire urinary tract for tumour, stone, or other pathology
- CT urogram = CT with IV contrast in nephrographic and excretory phases → visualises kidneys, ureters, bladder
| Timing | Investigation | Key Findings / Interpretation |
|---|---|---|
| ACUTE | Bladder scan | ≥ 300 mL = retention; ≥ 1 L = chronic [2] |
| Catheterisation (diagnostic + therapeutic) | Volume drained confirms diagnosis; send urine for analysis | |
| DRE | Prostate (size/consistency/tenderness), faecal loading, anal tone | |
| Neurological exam | Sensory level, perineal sensation, lower limb power/reflexes | |
| AFTER CATHETERISATION | CBC | Leukocytosis (infection/urosepsis) |
| RFT | Elevated creatinine → obstructive nephropathy | |
| LFT | Baseline | |
| Catheterised urine: biochemistry, microscopy, C/ST | UTI, haematuria, crystals | |
| KUB | Stones or faecal loading [2] | |
| DO NOT check PSA | False elevation during AROU — defer 4–6 weeks [2][8] | |
| ELECTIVE (after acute episode) | IPSS | Quantify LUTS severity; guide treatment |
| Uroflowmetry + PVR | Screen for BOO; Qmax < 10 = 90% obstructed [8] | |
| USG kidney/ureter | If large PVR, haematuria, or Hx stone [7] | |
| TRUS | Before 5-ARI or surgery [8] | |
| Cystoscopy | Haematuria, suspected stricture/tumour [8] | |
| Urodynamics | Gold-standard for BOO; atypical cases, suspected neurogenic bladder, failed intervention [7][8] | |
| PSA (4–6 weeks later) | Only if life expectancy > 10 years + counselled [8]; r/o CA prostate | |
| MRI spine | Urgently if neurological red flags |
Investigation Pitfalls to Remember
- PSA during AROU = false elevation → defer 4–6 weeks [2][8]
- Normal uroflowmetry does NOT exclude BOO — 18% still obstructed despite Qmax > 15 mL/s [7]
- Uroflowmetry cannot distinguish BOO from DUA — both give low Qmax; need urodynamics to differentiate [3][7]
- Normal DRE does NOT exclude BPH — transition zone enlargement is not palpable from the rectum [3]
- Uroflowmetry requires voided volume > 150 mL to be a valid test [7]
- BPH does NOT necessarily cause outflow obstruction — size alone doesn't determine symptoms [3]
Since PSA is so commonly tested in exams and frequently misunderstood, here is a comprehensive summary for the elective workup phase:
PSA (Prostate-Specific Antigen) [3]:
- Prostate-specific but NOT prostate-cancer-specific [3]
- Half-life = 2–3 days [3]
- PSA > 1.5 ng/mL is a useful marker for prostatic enlargement and predicts increased risk of BPH progression [3]
Interpretation [3]:
- PSA < 4 ng/mL = Normal
- PSA ≥ 4 ng/mL = Cutoff for diagnostic prostate biopsy
- PSA 4–10 ng/mL = 20% chance of cancer (the "grey zone")
- PSA ≥ 10 ng/mL = 50% chance of cancer
- During AROU or UTI (false elevation)
- If patients have < 10 years of life expectancy (unless clinically obvious disease like palpable nodule on DRE) [3]
High Yield Summary
- AROU is a clinical diagnosis: inability to void + full bladder (scan ≥ 300 mL) + painful + sudden onset
- Bladder scan is the first-line differentiator: full = retention; empty = anuria/oliguria
- ≥ 1 L on catheterisation suggests CROU — look for neurological cause
- Acute investigations: CBC, RFT, LFT, catheterised urine (biochemistry, microscopy, C/ST), KUB
- DO NOT CHECK PSA during AROU — causes false elevation; defer 4–6 weeks
- DRE: must do in all patients; assesses prostate, faecal loading, anal tone; normal DRE does NOT exclude BPH
- Uroflowmetry: screening for BOO; valid only if voided > 150 mL; Qmax < 10 = 90% obstructed; but cannot distinguish BOO from DUA
- Urodynamics: gold standard for BOO; high pressure + low flow = BOO; low pressure + low flow = DUA
- Outflow obstruction = high pressure, low flow on urodynamics [3]
- TRUS: before 5-ARI or surgical planning; cystoscopy: for haematuria, suspected stricture/tumour
- MRI spine: urgently if neurological red flags (sensory level, weakness, ↓ anal tone)
- IPSS: quantifies LUTS severity (mild 1–7, moderate 8–19, severe 20–35); guides treatment but is NOT a diagnostic tool
Active Recall - Diagnosis and Investigations of AROU
References
[1] Lecture slides: GC 180. Benign prostatic hyperplasia, bladder outlet obstruction and urinary retention.pdf (pp. 23, 24, 30, 33) [2] Senior notes: Ryan Ho Urogenital.pdf (pp. 164–167, 170–173); Ryan Ho Fundamentals.pdf (pp. 349–352, 355–356) [3] Senior notes: felixlai.md (AROU section – diagnosis, physical examination, biochemical tests, specific tests; BPH section – PSA interpretation) [4] Senior notes: maxim.md (AROU section – physical examination, investigations) [5] Senior notes: Ryan Ho Critical Care.pdf (p. 25 — AKI aetiology) [7] Senior notes: Ryan Ho Urogenital.pdf (pp. 170–173); Ryan Ho Fundamentals.pdf (pp. 355–356) — uroflowmetry, IPSS, urodynamics, BPH workup [8] Lecture slides: Benign Prostatic Hyperplasia.pdf (pp. 12, 18) [9] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p. 17 — IVU)
Management Algorithm and Treatment Modalities
The management of AROU has two distinct phases that must be understood sequentially:
-
Phase 1 — Acute management: Relieve the patient's distress by decompressing the bladder. This is an emergency. The patient is in pain, the bladder is at risk of further damage, and post-renal AKI may be developing. You decompress first, ask questions later.
-
Phase 2 — Subsequent management: Once the catheter is in and the patient is comfortable, you work out the underlying cause, treat reversible precipitants, and plan for either trial without catheter (TWOC) or definitive surgical management.
Clinical Management of Urinary Retention [1] — the lecture dedicates a specific section to this.
2. Phase 1: Acute Bladder Decompression
This is the immediate priority. Think of it like chest compressions in a cardiac arrest — do it first, everything else follows.
2.1 Urethral Catheterisation (First-Line)
Immediate bladder decompression by urethral catheterisation (first-line) by 14–18Fr Foley's catheter [2]
- Check for contraindications first (see below)
- Aseptic technique: clean genital area with aqueous hibitane (chlorhexidine), drape surrounding areas [2][4]
- Intraurethral local anaesthetic: apply xylocaine (lignocaine) jelly around meatal opening → milk jelly down urethra → wait 5 minutes for anaesthesia to take effect [2]
- Insertion: use forceps to hold 14Fr Foley's catheter → insert all the way down using no-touch technique [2] — the key point is to insert the full length, especially in males with a long urethra, before inflating the balloon. If you inflate prematurely while the tip is still in the prostatic urethra, you will cause severe urethral trauma
- Confirm position: observe for urine flow from the catheter
- Fixation: inject 10 mL of water (water for injection, NOT saline) into balloon → withdraw catheter until resistance is felt (balloon sits at bladder neck) [2]
- Connect to urine drainage bag
- Record the volume drained — this is diagnostically important:
- Send catheterised urine for biochemistry, microscopy, C/ST [2]
- Monitor hourly urine output (Q1H) — important for detecting post-obstructive diuresis [3]
| Sex | Standard Size | Rationale |
|---|---|---|
| Males | 14 or 16 Fr [3] (range 14–18Fr [2]) | Male urethra is longer (~20 cm) and passes through the prostate; 14Fr is comfortable yet large enough for adequate drainage |
| Females | 12 or 14 Fr [3] | Female urethra is shorter (~4 cm) and wider; smaller catheter suffices |
Catheter material [3]:
- Latex = short-term use (maximum 2 weeks) — yellow tube
- Silicone = long-term use (maximum 4 weeks) — transparent tube
Types of catheter [3]:
- Standard 2-way: one port for urine drainage, one for balloon inflation — standard for AROU
- 3-way (triple-lumen): additional irrigation channel for clot retention — used for haematuria with clot formation to allow continuous bladder irrigation [3]
Failure to pass into bladder can be due to [2][4]:
| Situation | Likely Cause | Solution | Why It Works |
|---|---|---|---|
| Cannot advance past prostatic urethra | Enlarged prostate (BPH) | Use thicker catheter (20–22 Fr) [2][4] | A thicker catheter is stiffer — it has more rigidity to navigate through the compressed prostatic urethra. Think of it like a garden hose vs a limp straw — the stiffer one pushes through better |
| Catheter stuck proximally along penile urethra / Hx of instrumentation or TURP | Urethral stricture | Use thinner catheter (10–12 Fr) [2][4] | The urethral lumen is narrowed by fibrosis — a thinner catheter can squeeze through the tight segment |
If standard troubleshooting fails [4]:
- Tiemann catheter: curved-tip catheter specifically designed for BPH — the angled tip navigates the elevated prostatic urethra
- Cystoscopic-guided Foley insertion: pass a flexible cystoscope first, then railroad the catheter over a guidewire
- Urethral dilators: for strictures — progressively dilate the narrowed segment
- Suprapubic catheterisation (SPC): the definitive fallback (see below)
| Type | Contraindication | Rationale |
|---|---|---|
| Absolute | Urethral injury — signs: blood at urethral meatus, high-riding prostate on DRE [2][3][4] | Passing a catheter through an injured urethra can convert a partial tear into a complete transection → devastating complication. If you suspect urethral injury (e.g., pelvic fracture + blood at meatus), do a retrograde urethrogram first |
| Relative | Urethral stricture [3] | Risk of creating false passage; may need specialist guidance or SPC |
| Relative | Recent urinary tract surgery: radical prostatectomy, urethral reconstruction, presence of artificial sphincter [3] | Fresh anastomoses can be disrupted by catheter passage → urethral damage, incontinence |
| Relative | Acute prostatitis [3] | Catheterisation through an acutely inflamed prostate is painful and may worsen infection; SPC is preferred in severe prostatitis |
Suprapubic catheterisation (SPC) [2]
- Failed urethral catheterisation
- History of urethral trauma (e.g., straddle injury)
- Long-term bladder drainage expected ( > 3 weeks) [2]
Why SPC over long-term urethral catheter? [3]:
- Prevents urethral trauma and stricture formation
- Prevents periurethral abscess
- Prevents urinary sphincter dysfunction leading to incontinence
- Reduces catheter-associated UTI (CAUTI)
- Allows assessment of patient's ability to void before removing catheter (can clamp SPC and let patient try to void naturally through the urethra)
Procedure [2]:
- LA injected 2 finger-breadths (2FB) above pubic symphysis (~2 fingers above pubic symphysis [4])
- Small incision made in skin/fascia → insert trocar-type suprapubic tube → catheter advanced over trocar → sutured in place
- Look for gush of urine [2]
Contraindications to SPC [2][3]:
- Non-distended bladder — if the bladder is empty/small, you risk missing it entirely and perforating bowel instead
- Uncorrected bleeding tendency — procedure involves a skin incision and puncture through the abdominal wall
- Known or suspected urothelial cancer — risk of tumour seeding along the catheter tract
Complications of SPC [2]:
- Bowel perforation (if bladder not adequately distended and bowel loops interposed)
- Rectal injury (overshooting)
- Haematuria
- Wound infection
SPC Safety Rule
Never perform SPC on a non-distended bladder. The bladder must be palpable and confirmed on ultrasound to be adequately full. If the bladder is empty, the SPC trocar will pass straight through an empty pelvic space and into bowel or rectum.
3. Phase 2: Subsequent Management
Once the catheter is in and the patient is stabilised, the management pivots to:
- Treat reversible precipitants
- Start medical therapy (α-blocker)
- Plan trial without catheter (TWOC)
- Address definitive management of the underlying cause
Treat reversible causes: stop offending drugs, treat constipation (e.g., Fleet enema) and UTI [4]
| Precipitant | Management |
|---|---|
| Offending drugs (cold meds, anticholinergics, opioids) | Stop or switch medications |
| Constipation/faecal impaction | Fleet enema, lactulose, manual disimpaction if needed |
| UTI | Appropriate antibiotics based on C/ST results |
| Immobility | Mobilise patient as early as possible |
| Post-operative (anaesthesia-related) | Often self-resolving once anaesthetic wears off; TWOC usually successful |
Prescribe alpha-blocker (e.g., Xatral/alfuzosin) + trial wean-off catheter (TWOC) later [4]
The rationale: α₁-adrenergic receptors are abundant in the smooth muscle of the prostate stroma and bladder neck. Blocking these receptors relaxes the smooth muscle → reduces the dynamic component of bladder outlet obstruction → makes it easier for the detrusor to overcome the remaining obstruction when the catheter is removed.
Starting an α-blocker before TWOC significantly improves the success rate of TWOC — studies show ~50–60% success with α-blocker vs ~30–40% without.
TWOC is the pivotal management decision after the acute episode. The catheter is typically left in for ~2 days [3], during which time the α-blocker takes effect, precipitants are corrected, and the overdistended detrusor has time to recover some contractile function.
Process [4]:
- Remove the catheter (usually in the early morning to allow the whole day for voiding assessment)
- Observe urine output and perform post-void bladder scan [4]
- Patient attempts to void naturally
- Check post-void residual (PVR) by bladder scan
Outcomes:
| Outcome | Next Step |
|---|---|
| Successful TWOC (patient voids with acceptable PVR < 200–400 mL) | Discharge with α-blocker; follow-up in urology OPD for definitive BPH management |
| Re-catheterise if bladder scan > 400 mL [4] | Re-TWOC / long-term Foley / clean intermittent self-catheterisation (CISC) [4] |
| Failed repeated TWOC | Arrange definitive surgical intervention (e.g., TURP) |
TWOC is contraindicated if obstructive uropathy present (RFT improves after Foley insertion) [4] — if the creatinine drops significantly after catheterisation, this means the obstruction was causing bilateral back-pressure → post-renal AKI → upper tract damage. Removing the catheter would re-obstruct and cause further renal injury. These patients need to keep the catheter in until definitive surgery.
Why Not Just Remove the Catheter Immediately?
The overdistended detrusor needs time to recover. Remember, overdistension stretches actin-myosin beyond optimal overlap → ineffective contraction. Leaving the catheter in for 48–72 hours (while on an α-blocker) gives the muscle fibres time to recover their length-tension relationship. Additionally, α-blockers need ~48 hours to reach therapeutic effect.
If the patient fails TWOC and is not fit for surgery (or while awaiting surgery):
| Option | Description | Preferred When |
|---|---|---|
| Long-term indwelling Foley catheter | Indwelling urethral catheter, changed every 4–6 weeks | Short-term bridging; patient preference |
| Suprapubic catheter (SPC) | Preferred for long-term drainage > 3 weeks [2] | Better for long-term use; fewer urethral complications |
| Clean intermittent self-catheterisation (CISC) | Patient self-catheterises 4–6× daily using a clean single-use catheter | Gold standard for long-term bladder management in neurogenic bladder; requires adequate dexterity and cognition |
4. Definitive Management of the Underlying Cause — BPH
Since BPH accounts for 53% of AROU [1], BPH management is the most commonly tested definitive treatment.
Medical therapy indications [4][7]:
| Drug Class | Drug Examples | Mechanism | Indications | Key Side Effects | Contraindications/Cautions |
|---|---|---|---|---|---|
| α₁-adrenergic blockers (most commonly used) | Non-selective: prazosin (Minipress), terazosin (Hytrin), doxazosin (Cardura), alfuzosin (Xatral) [4] Selective (α₁A): tamsulosin (Harnal), silodosin (Rapaflo) [4] | Relax smooth muscles in prostate and bladder neck (NOT bladder body) [4] → reduces dynamic obstruction → improves flow within days | Moderate-to-severe LUTS (not storage-predominant) [7] | Non-selective: more orthostatic hypotension, nasal congestion, dizziness, tiredness [4] Selective (α₁A): more retrograde ejaculation [4] | To reduce side effects: slow titration, subtype-selective (α₁A), slow-release formulations [4] |
| 5α-reductase inhibitors (5-ARI) | Finasteride, dutasteride [4] | Reduce DHT → decrease size of prostate + decrease vascularity (less bleeding) + progression prevention [4]. DHT is the active androgen that drives prostatic stromal growth; blocking its production causes prostate to shrink by ~20–30% over 6–12 months | Moderate-to-severe LUTS + large prostate ( ≥ 30–40 mL on TRUS) / IPSS ≥ 12 [4] 2nd line or in combination with α₁-blockers [4] | Erectile dysfunction (10%), gynaecomastia [4] 50% decrease in PSA → must multiply PSA by 2 when screening for CA prostate [4] | Slow onset: 3–6 months for maximum effect [4] — not useful for acute symptom relief; mainly for long-term disease modification |
| α₁-blocker + 5-ARI combination | Above drugs combined | Dual mechanism: immediate α₁-blockade + long-term prostate shrinkage | Moderate-to-severe LUTS + increased risk of disease progression [7] | Combination of above side effects | Large prostate with significant symptoms and risk factors for progression |
| PDE5 inhibitors | Tadalafil (Cialis) [4] | PDE5-mediated reduction in smooth muscle and endothelial cell proliferation; increases smooth muscle relaxation and perfusion to prostate and bladder [3] | Especially useful for those with erectile dysfunction [7]; moderate-to-severe LUTS | Hypotension, blue/blurred vision, hearing loss, flushing, headache, dyspepsia [3] | Avoid if using nitrate [4] (severe hypotension risk) |
| Muscarinic blockers / β₃ agonists | Oxybutynin, solifenacin / Mirabegron (β₃ agonist) [3] | Muscarinic blockers: block M₃ on detrusor → reduce involuntary contractions β₃ agonists: activate β₃ receptors → relax detrusor during filling | Storage-predominant moderate-to-severe LUTS; residual storage symptoms after α₁-blocker/PDE5I treatment [7] | Anticholinergics: dry mouth, constipation, urinary retention β₃ agonists: hypertension, UTI | Caution if post-void residual > 150 mL [7] — anticholinergics can worsen retention! β₃ agonist (Mirabegron) does not have the same concern for urinary retention as anticholinergics [3] |
Why α-Blockers Work Fast but 5-ARIs Take Months
α-blockers relax smooth muscle (the dynamic component) — this is like turning off a switch. The effect is almost immediate (days). 5-ARIs reduce the physical size of the prostate (the static component) — this requires blocking DHT-driven growth and waiting for prostate tissue to involute. Tissue remodelling takes months. This is why the two drugs are complementary: α-blockers for immediate relief, 5-ARIs for long-term disease modification.
| Modality | Mechanism |
|---|---|
| Thermotherapy: HIFU, TUMT (transurethral microwave therapy) | Heat-induced coagulative necrosis of prostate tissue |
| UroLift | Mechanical implants that hold prostatic lobes apart, away from the urethra |
| Steam treatment (Rezum) | Inject water vapour into prostate → induces coagulative necrosis |
| Prostatic artery embolisation (PAE) | Reduce part of the blood supply to the prostate → ischaemic shrinkage |
4.4 Surgical Treatment
Indications for surgery [3][4][7]:
Absolute indications (complications of BPH) [7]:
- Recurrent acute retention of urine (AROU) — failed TWOC [3]
- Recurrent urinary tract infection (UTI) [3]
- Recurrent haematuria [3]
- Renal insufficiency secondary to BPH (obstructive uropathy) [3]
- Bladder stones [7]
Relative indication [7]:
- Bothersome LUTS refractory to or cannot tolerate medical treatment [3]
TURP decreases urinary symptom score (IPSS), decreases PVR and increases maximal urinary flow rate [3]
Monopolar TURP [3]:
- Resectoscope loaded with monopolar diathermy loop is introduced into bladder
- Continuous irrigation using non-conductive solution containing glycine is used to distend the bladder and wash away blood and tissue fragments
- Glycine is better than distilled water as non-conductive irrigant since it causes less TUR syndrome comparatively
- Saline solution CANNOT be used for monopolar resection because it is a good conductor of electricity, diffuses power and does not allow cutting or cauterisation of tissue [3]
- Strips of prostate tissue are resected under direct vision until the prostatic fibrous capsule is reached
- Prostate chips evacuated and bleeding controlled with electrocautery
- Post-operative: 3-way Foley to irrigate bladder with NS to avoid clot retention [4]
- Saline is used as the irrigant in bipolar — eliminates the risk of hyponatraemia in TUR syndrome [3]
- More expensive than monopolar TURP [3]
- Process is slower due to smaller probe size; poorer haemostasis [7]
- Usually only use bipolar for larger prostates [7]
Surgical modality by prostate size [7]:
| Prostate Size | Recommended Procedure |
|---|---|
| Small prostate < 30 mL + no middle lobe | TUIP (Transurethral Incision of Prostate) — longitudinal incision to widen bladder neck without removing tissue; lower morbidity [7] |
| Moderate prostate 30–80 mL | Bipolar or monopolar TURP [7] |
| Large prostate > 80 mL | Transurethral enucleation (e.g., Holmium/Thulium laser enucleation) [7] or open prostatectomy |
| Complication | Mechanism / Details | Incidence |
|---|---|---|
| Bleeding / haematuria | Trauma to prostatic venous sinuses; secondary infection (prostatitis) | Bleeding requiring transfusion: ~1% [3] |
| TUR syndrome (Post-prostatectomy syndrome) | Hyponatraemia due to systemic absorption of hypotonic irrigating fluid (glycine) [3][4] Pathophysiology: dilutional hyponatraemia + fluid overload + glycine toxicity [4] Risk factors: long operating time, e.g., massive prostate [4] Signs/symptoms: nausea (first symptom), confusion, cerebral oedema, visual disturbance [4] Management: manage as hyponatraemia (electrolytes, serum osmolality, volume status), hypertonic saline [4] Prevention: use bipolar (NS as irrigating fluid), limit volume < 1 L and irrigation pressure < 60 mmHg [4] | Variable |
| Retrograde ejaculation | 70–80% — due to resection of bladder neck [4]; semen enters bladder instead of exiting via urethra because the bladder neck can no longer close during ejaculation | Very common |
| Urethral stricture | Urethral instrumentation [4] causes scarring | Variable |
| Urinary incontinence | ~1% [3]; urge incontinence (early, due to detrusor irritability) / stress incontinence (late, due to sphincter damage) [4] | |
| Erectile dysfunction | Thermal injury to neurovascular bundle adjacent to prostate | Variable |
TUR Syndrome — Why Monopolar TURP Is Dangerous in Large Prostates
During monopolar TURP, the irrigant must be non-conductive (glycine). The prostatic venous sinuses are opened during resection, and glycine is absorbed directly into the bloodstream. Longer operating time (larger prostate) = more absorption = greater risk. Glycine causes: (1) dilutional hyponatraemia (water follows glycine osmotically), (2) fluid overload (absorbed volume), (3) direct neurotoxicity from glycine metabolites (ammonia → visual disturbance, confusion). Bipolar TURP uses saline, eliminating this risk entirely, which is why it is preferred for larger prostates [3][4][7].
| Technique | Description | Advantage | Indication |
|---|---|---|---|
| Transurethral enucleation (Holmium/Thulium laser) | Laser enucleation of adenoma → morcellation for removal | Saline irrigant (no TUR syndrome); less bleeding; effective for large prostates | Large prostate > 80 mL [7] |
| Ablative techniques (PVP/Green Laser, RFA, Rezum) | Tissue destruction without removal | Less bleeding; alternative to TURP in patients with bleeding tendency or poor operative risk [7]; less post-op irritative symptoms | No histological specimen obtained; decreased durability [7] |
| Open / robotic prostatectomy | Open surgical enucleation of adenoma via suprapubic or retropubic approach | Gold standard for very large prostates ( > 80–100 mL); complete removal | Very large prostates; failed TURP |
| Metallic stent | Temporary urethral stent to keep prostatic urethra open | Avoids surgery | Very unfit patients [4] |
5. Management of Specific Scenarios
- Cause: Severe haematuria (from BPH bleeding, bladder tumour, post-TURP) → blood clots fill bladder → outlet obstruction
- Management: 3-way Foley catheter [3] → continuous bladder irrigation with normal saline to wash out clots → investigate and treat the source of bleeding
- If clots are too large for irrigation: manual bladder washout with bladder syringe; cystoscopy with clot evacuation if refractory
- Immediate: catheterise to decompress bladder
- Urgent: MRI spine → if cord compression confirmed → neurosurgical decompression
- Long-term: clean intermittent self-catheterisation (CISC) is the gold standard for neurogenic bladder management
- Usually self-limiting once anaesthesia wears off
- TWOC typically successful within 24–48 hours
- If recurrent: investigate for underlying BOO (may unmask subclinical BPH)
- Stop the offending drug
- Catheterise and TWOC after drug has been discontinued
- Usually resolves; if recurrent, investigate for underlying BPH
These occur after catheterisation and must be anticipated and managed:
| Complication | Definition / Mechanism | Management |
|---|---|---|
| Post-obstructive diuresis | Diuresis > 200 mL/h for ≥ 2 hours [3][4] after decompression. Represents the body's attempt to excrete excess fluid, solutes (urea, Na⁺), and water retained during the period of obstruction. Also due to osmotic diuresis from accumulated urea and loss of medullary concentrating gradient. Primarily a problem of chronic (not acute) retention [3] | Monitor hourly urine output closely. Patients usually can manage by increasing oral fluid intake [3]. Isotonic saline replacement is indicated if patients are unable to increase fluid intake [3]. Monitor electrolytes (risk of hyponatraemia, hypokalaemia). Do NOT remove Foley catheter — may lead to hydronephrosis [3] |
| Haemorrhage ex vacuo | Transient haematuria due to mucosal disruption [4] when the overdistended bladder suddenly decompresses. Small mucosal blood vessels that were compressed by the full bladder begin to bleed when pressure is released | Usually self-limiting; maintain catheter drainage; if persistent, consider continuous bladder irrigation with 3-way catheter |
| Transient hypotension [3] | Sudden decompression of a large-volume bladder → abrupt ↓ intra-abdominal pressure → venous pooling in the splanchnic bed → ↓ preload → ↓ BP. Also vagal response from relief of pain | IV fluids; gradual decompression (some advocate clamping catheter after every 500 mL and releasing — though evidence for this is debated) |
| UTI / CAUTI | Catheter itself is a foreign body that acts as a nidus for biofilm and bacterial colonisation | Aseptic insertion technique; remove catheter as soon as possible; avoid long-term catheterisation if possible |
| Urethral stricture (late) | Repeated or traumatic catheterisation causes urethral mucosal injury → fibrosis → stricture | Minimise catheter duration; use appropriate size; consider SPC for long-term |
Post-Obstructive Diuresis — Don't Panic, But Don't Ignore It
Post-obstructive diuresis is expected after relieving chronic or severe acute retention. It is the kidneys' way of dumping retained solutes and water. The danger is not the diuresis itself — it is under-replacement leading to dehydration and electrolyte disturbance. Monitor Q1H urine output and match IV fluid replacement if the patient cannot drink enough. The diuresis typically resolves within 24–48 hours once the excess is cleared.
| Phase | Action |
|---|---|
| Immediate | Urethral catheterisation (14–18Fr Foley) → record volume → send urine |
| If catheter fails | Troubleshoot (thicker/thinner catheter, Tiemann) → SPC if all fail |
| Post-catheterisation | Bloods (CBC, RFT), catheterised urine (C/ST), KUB; NOT PSA |
| Treat precipitants | Stop offending drugs, treat constipation, treat UTI |
| Start α-blocker | Alfuzosin/tamsulosin — reduces dynamic obstruction |
| Monitor | Q1H urine output → watch for post-obstructive diuresis |
| TWOC | ~48 hours later; re-catheterise if PVR > 400 mL |
| Failed TWOC | Re-TWOC / long-term catheter / CISC |
| Definitive | Elective TURP 4–6 weeks after AROU [4] (lower intra-operative risk than emergency) |
| Ongoing BPH | IPSS, uroflowmetry, PSA (4–6 weeks), TRUS → guide long-term management |
High Yield Summary
- Acute management priority = bladder decompression via urethral catheterisation (14–18Fr Foley); SPC if urethral route fails or is contraindicated
- Contraindications to urethral catheter: blood at meatus, high-riding prostate (urethral injury); recent urological surgery; severe prostatitis
- SPC contraindications: non-distended bladder, bleeding tendency, urothelial cancer
- Catheter troubleshooting: stuck at prostate → thicker catheter (20–22Fr); stuck at penile urethra → thinner catheter (10–12Fr)
- After catheterisation: treat reversible precipitants (drugs, constipation, UTI), start α-blocker, plan TWOC at ~48 hours
- TWOC contraindicated if obstructive uropathy present (RFT improves after catheterisation) — keep catheter, proceed to surgery
- α-blockers (alfuzosin, tamsulosin): relax prostatic smooth muscle → immediate relief; 5-ARIs (finasteride, dutasteride): shrink prostate → 3–6 months to work
- TURP indications: recurrent AROU (failed TWOC), recurrent UTI, recurrent haematuria, renal insufficiency from BPH, bladder stones, refractory LUTS
- TUR syndrome: dilutional hyponatraemia + fluid overload + glycine toxicity; prevented by bipolar TURP (uses saline)
- Post-obstructive diuresis: > 200 mL/h for ≥ 2h; monitor Q1H urine output; replace fluids if patient cannot drink
- Elective TURP best done 4–6 weeks after AROU (not emergency) — lower intra-operative risk
- Long-term options if unfit for surgery: long-term Foley/SPC, CISC, metallic stent
Active Recall - Management of AROU
References
[1] Lecture slides: GC 180. Benign prostatic hyperplasia, bladder outlet obstruction and urinary retention.pdf (p. 54) [2] Senior notes: Ryan Ho Urogenital.pdf (pp. 167, 176); Ryan Ho Fundamentals.pdf (p. 352) [3] Senior notes: felixlai.md (AROU treatment section, urinary catheterisation section, TURP section) [4] Senior notes: maxim.md (AROU subsequent management, BPH management, TURP complications) [5] Senior notes: Ryan Ho Critical Care.pdf (p. 26 — AKI management) [7] Senior notes: Ryan Ho Urogenital.pdf (pp. 173, 176); Ryan Ho Fundamentals.pdf (pp. 355–356) — BPH treatment algorithm, surgical indications
Complications of Acute Retention of Urine
Complications of AROU fall into two broad categories that are conceptually distinct:
- Complications of the retention itself — what happens to the urinary tract (and the patient) if urine sits trapped in a distended bladder
- Complications of decompression (catheterisation) — what happens after you relieve the retention
Both must be anticipated, monitored for, and managed. Let's work through each from first principles.
1. Complications of the Retention Itself
These are the consequences of a distended, obstructed urinary system. Think of it as a plumbing system under back-pressure: the blockage at the outlet causes pressure to build up backwards through the entire system — bladder → ureters → kidneys.
Consequence of BOO [1]:
- Retention of urine — acute or chronic
- Recurrent UTI
- Formation of bladder calculi
- Hydroureter and hydronephrosis
- Renal impairment / ARF (Obstructive uropathy) [1]
| Feature | Detail |
|---|---|
| Mechanism | Stagnant urine in a distended bladder is a perfect culture medium for bacteria. Normal voiding is one of the body's most important defence mechanisms against UTI — the "washout effect" flushes bacteria out of the bladder regularly. When voiding stops, bacteria proliferate unopposed. The presence of a catheter (a foreign body) further compounds the risk by providing a surface for biofilm formation and acting as a direct conduit for ascending bacteria |
| Clinical features | Fever, dysuria, cloudy/malodorous urine, suprapubic pain (which may be masked by the existing retention pain); can escalate to urosepsis (SIRS with urinary source): rigors, tachycardia, hypotension, confusion |
| Why it matters | Recurrent UTI is listed as a consequence of BOO [1] and is an absolute indication for surgical intervention (TURP) in BPH [3]. Urosepsis in the context of obstructed, infected urine is a life-threatening emergency requiring urgent decompression + IV antibiotics |
| Management | Catheterisation (drain the infected reservoir), empirical IV antibiotics (e.g., IV co-amoxiclav or piperacillin-tazobactam depending on local protocol), blood cultures, adjust based on C/ST. Long-term catheterisation carries risk of UTI/urosepsis, trauma, stones, urethral strictures, prostatitis and SCC of bladder [2] |
| Feature | Detail |
|---|---|
| Mechanism | Formation of bladder calculi [1]. Stagnant urine becomes supersaturated with crystalloids (calcium, oxalate, phosphate, uric acid). Normally, regular voiding prevents crystal nucleation. In retention, prolonged contact time allows crystals to nucleate, grow, and aggregate into stones. Infection (particularly with urease-producing organisms like Proteus mirabilis) further promotes stone formation by splitting urea into ammonia → alkalinising the urine → precipitating struvite (magnesium ammonium phosphate) stones |
| Clinical features | Strangury (painful, frequent urination of small volumes expelled only by straining), terminal haematuria, suprapubic pain that worsens at end of micturition (stone shifts to bladder neck), recurrent UTI with urease-producing organisms |
| Why it matters | Bladder stones are a consequence of BOO [1] and an absolute indication for surgery [2][7]. They also perpetuate a vicious cycle: stones irritate the bladder wall → detrusor overactivity → worsening LUTS; stones harbour bacteria → recurrent UTI |
| Management | Cystolitholapaxy (endoscopic stone fragmentation and removal); address underlying BOO (TURP) to prevent recurrence |
| Feature | Detail |
|---|---|
| Mechanism | Hydroureter and hydronephrosis [1]. When the bladder cannot empty, intravesical pressure rises progressively. Once intravesical pressure exceeds the pressure in the distal ureters, urine can no longer drain from the kidneys into the bladder. Urine "backs up" → ureters dilate (hydroureter) → renal pelvis and calyces dilate (hydronephrosis). In the context of BOO, this is bilateral because the obstruction is below the level of both ureteric orifices. In chronic retention, intravesical pressure can remain elevated for weeks to months, causing sustained bilateral upper tract dilatation |
| Clinical features | Often insidious and asymptomatic until late. May present as bilateral loin pain, renal impairment discovered incidentally, or bilateral ballotable kidneys on examination (in severe cases) [2]. Fever with hydronephrosis = pyonephrosis (infected hydronephrosis) — a surgical emergency requiring urgent drainage (PCN or JJ stent) |
| Why it matters | Hydronephrosis from retention leads directly to the next complication — obstructive uropathy/renal failure. It is detectable on ultrasound (USG KUB) and its presence indicates significant back-pressure |
| Management | Bladder decompression (catheterisation) relieves the distal obstruction, and the hydronephrosis typically resolves. If it persists despite bladder drainage, suspect a concurrent ureteric pathology |
| Feature | Detail |
|---|---|
| Mechanism | Renal impairment / ARF (Obstructive uropathy) [1]. Sustained back-pressure from the distended bladder → bilateral hydronephrosis → ↑ pressure in Bowman's capsule → opposes the filtration pressure driving GFR → GFR drops → creatinine rises → post-renal AKI. If prolonged, the renal parenchyma undergoes tubular atrophy and interstitial fibrosis → irreversible chronic kidney disease. Post-renal disease ( < 10%) due to obstructive uropathy (must be bilateral) [5], but in BOO, the obstruction IS bilateral by definition (single point of obstruction below both ureteric orifices) |
| Clinical features | Elevated creatinine on blood tests, uraemic symptoms (vomiting, lethargy, drowsiness [2], confusion, pruritus, anorexia), oliguria (paradoxically — the kidneys cannot filter effectively), fluid overload, hyperkalaemia. Usually rare in AROU, more likely in CROU [2] — because chronic retention allows prolonged sustained back-pressure, whereas AROU is typically relieved quickly |
| Why it matters | Renal impairment from BPH is an absolute indication for surgery [3]. TWOC is contraindicated if obstructive uropathy present (RFT improves after Foley insertion) [4] — because removing the catheter would re-obstruct and cause further renal damage |
| Management | Immediate bladder decompression → monitor renal function (creatinine should start improving within 24–48 hours). Management of life-threatening complications of AKI [5]: hyperkalaemia (IV calcium, insulin-dextrose, polystyrene sulphonate), fluid overload (diuretics, dialysis if refractory), metabolic acidosis (bicarbonate, dialysis). Anticipate post-obstructive diuresis (see below). Consider haemodialysis if refractory (indications: Acidosis, Electrolyte imbalance, Intoxication, Overload, Uraemia — "AEIOU") [5] |
| Feature | Detail |
|---|---|
| Mechanism | Acute overdistension stretches detrusor smooth muscle fibres beyond their optimal actin-myosin overlap (the length-tension relationship). The bladder wall becomes thin, atonic, and unable to generate effective contraction. In chronic retention with BOO, the detrusor initially compensates by hypertrophy (thicker muscle to overcome higher resistance) → bladder wall becomes trabeculated (thickened muscle bundles visible as ridges). Eventually, the detrusor decompensates → diverticula (outpouchings of mucosa between hypertrophied muscle bundles) → further residual urine → worsening cycle. Complications of chronic retention: bladder stones, UTI, overflow incontinence, hernia due to chronic straining, obstructive uropathy [7] |
| Clinical features | Failed TWOC (detrusor too weak to void even after obstruction is relieved), persistent elevated post-void residual, overflow incontinence (constant dribbling from an overfull, atonic bladder), bladder diverticula on imaging |
| Why it matters | If the detrusor is severely decompensated, even a successful TURP may not restore normal voiding — the patient may need long-term CISC. This is why we try not to let AROU persist for too long |
| Feature | Detail |
|---|---|
| Mechanism | When the bladder is so full that intravesical pressure intermittently exceeds urethral resistance, small amounts of urine "overflow" and leak out. Overflow incontinence: constant dribbling (especially at night) with associated retention of urine. Mechanism: BOO/DUA → bladder over-distension with continuous dribbling [7] |
| Clinical features | Paradoxical — the patient appears to be passing urine (dribbling) but is actually in retention. The bladder remains palpable. Patients may not recognise that they are retaining urine because they are "passing something" |
| Why it matters | Can be mistaken for normal voiding → retention goes unrecognised → progressive upper tract damage. Complications: UTI, bladder stones, obstructive uropathy [7] |
| Feature | Detail |
|---|---|
| Mechanism | Pain, discomfort, and autonomic disturbance from a grossly distended bladder can precipitate acute confusion in elderly patients with reduced cerebral reserve. "DELIRIUM" mnemonic includes R = Retention of urine or faeces as a recognised cause of delirium [6] |
| Clinical features | Acute confusion, agitation, disorientation (time > place > person), fluctuating consciousness, worse at night |
| Why it matters | Always check for urinary retention in a delirious elderly patient (bladder scan!) — treating the retention may resolve the delirium |
| Feature | Detail |
|---|---|
| Mechanism | In patients with spinal cord injury at T6 or above, bladder distension triggers a massive sympathetic response below the level of the lesion (uninhibited by descending control) → severe vasoconstriction below the lesion → dangerous hypertension. Baroreceptors above the lesion detect the hypertension and trigger a compensatory vagal (parasympathetic) response → bradycardia, flushing, and sweating above the lesion — but this cannot counteract the sympathetic storm below |
| Clinical features | Severe headache, hypertension (can be > 200 mmHg systolic), bradycardia, flushing/sweating above the lesion, pallor/gooseflesh below. Can cause stroke, seizures, or death if untreated |
| Why it matters | A medical emergency. Bladder distension (including AROU) is the most common trigger. Immediate management: sit the patient upright (orthostatic reduction in BP), catheterise immediately to relieve the distended bladder, loosen tight clothing. If hypertension persists: sublingual nifedipine or GTN patch |
2. Complications of Decompression (Post-Catheterisation)
These occur after you have done the right thing and catheterised the patient. They are largely predictable and manageable if anticipated.
Post-obstructive diuresis: > 200 mL/h urine × ≥ 2h or > 3L urine in 24h [2]
| Feature | Detail |
|---|---|
| Definition | Diuresis that persists after decompression of the bladder [3]. Defined as diuresis > 200 mL/hr for 2 hours [3][4] or > 3L urine in 24 hours [2] |
| Mechanism | Tubular damage → decreased concentrating ability → rapid fluid and solute loss [2]. During the period of obstruction, excess sodium, urea, and water accumulate in the body. Once the obstruction is relieved, the kidneys attempt to excrete this excess — this is the physiological component and is appropriate. However, the sustained back-pressure may have damaged the renal tubules (especially the concentrating mechanism in the loop of Henle and collecting ducts) → the kidneys lose the ability to reabsorb water and solutes appropriately → pathological diuresis that can lead to dangerous fluid and electrolyte depletion |
| Significance | Represents a physiological response to remove excess fluid in body (especially in CROU), but may result in fluid and electrolyte imbalance (pathological POD) [2]. Primarily a problem of chronic but not acute urinary retention [3] — because chronic retention allows greater accumulation of excess fluid and more tubular damage |
| Investigations | May have hypoNa, hypoK, hypovolaemia [2]. Check electrolytes Q4–6h during active diuresis |
| Management | Close monitoring of I/O, fluid/electrolyte status with appropriate replacement and resuscitation (prefer oral hydration, aim to replace 1/2 of urine output in the past hour) [2]. Patients usually can manage the increase in urine output by increasing oral fluid intake [3]. Isotonic saline replacement is indicated if patients are unable to increase fluid intake [3]. Do NOT remove Foley catheter since it may lead to hydronephrosis [3]. Remember to chart urine output Q2h [2] |
POD: The Practical Rule
After catheterising a patient for AROU (especially if high-volume or chronic), chart Q1–2H urine output. If UO > 200 mL/h for ≥ 2 hours: (1) check electrolytes urgently, (2) replace approximately half of the previous hour's urine output as IV normal saline if the patient cannot drink, (3) continue monitoring until diuresis settles (usually 24–48 hours). The physiological diuresis will self-resolve once the excess is cleared; the pathological diuresis from tubular damage may persist longer and needs ongoing replacement.
Haemorrhage ex-vacuo (transient haematuria due to mucosal disruption) [2][4]
| Feature | Detail |
|---|---|
| Mechanism | Bladder mucosal disruption with sudden emptying of a greatly distended bladder [2]. When the bladder is massively distended, the mucosal capillaries are compressed against the detrusor wall. Sudden decompression releases this tamponade effect → previously compressed vessels suddenly re-expand and bleed → haematuria. Think of it like releasing a tourniquet — the re-perfusion causes bleeding |
| Significance | Usually self-limiting, rarely significant [2]. Typically clears within hours. If it persists or is heavy, consider other sources (bladder tumour, BPH bleeding) |
| Management | Observation; ensure catheter is draining freely (clots can block the catheter → clot retention, which requires 3-way catheter with continuous bladder irrigation). If severe: manual bladder washout; cystoscopy with clot evacuation |
Transient hypotension due to vagovagal response or relief of pelvic venous congestion [2][3]
| Feature | Detail |
|---|---|
| Mechanism (1): Vasovagal | Sudden relief of pain and bladder distension triggers a parasympathetic (vagal) surge → bradycardia + vasodilation → ↓ BP. This is the "fainting with relief" mechanism |
| Mechanism (2): Pelvic venous decompression | A massively distended bladder compresses the pelvic veins, increasing venous return (and therefore preload) to the heart. When the bladder empties abruptly, this compression is released → pelvic venous pooling → ↓ venous return → ↓ preload → ↓ cardiac output → hypotension. Same principle as inferior vena cava compression by a gravid uterus |
| Management | Lie the patient flat; IV fluids if symptomatic. Some clinicians advocate gradual decompression (clamping the catheter after every 500 mL and releasing after 10–15 minutes) to prevent this, though evidence for this practice is limited and most guidelines do not recommend it routinely. The key is to monitor vitals during decompression |
| Feature | Detail |
|---|---|
| Mechanism | The catheter is a foreign body that disrupts normal urethral defence mechanisms, provides a surface for bacterial biofilm, and creates a direct conduit for ascending infection. Risk increases with duration of catheterisation (~5% per day for indwelling catheters) |
| Clinical features | Fever, pyuria, cloudy/malodorous urine, new confusion (in elderly). Note: asymptomatic bacteriuria is extremely common with indwelling catheters and should NOT be treated with antibiotics unless symptomatic |
| Management | Aseptic insertion technique; minimise catheter duration (daily evaluation of need); consider CISC over indwelling catheter; consider SPC for long-term drainage; treat symptomatic CAUTI with appropriate antibiotics |
| Long-term risk | Long-term catheterisation carries risk of: UTI/urosepsis, trauma, stones, urethral strictures, prostatitis, and SCC (squamous cell carcinoma) of bladder [2] — this is why long-term indwelling catheters are avoided whenever possible |
SCC of Bladder from Long-Term Catheterisation
Squamous cell carcinoma of the bladder is a rare but real complication of long-term catheterisation [2]. Chronic irritation by the catheter causes squamous metaplasia of the transitional epithelium → dysplasia → SCC. This typically requires years of continuous catheterisation and is most relevant in patients with chronic neurogenic bladder (e.g., spinal cord injury patients with permanent catheters). This is one reason CISC is preferred over indwelling catheters for long-term management.
| Feature | Detail |
|---|---|
| Mechanism | Urethral stricture [3] from traumatic or repeated catheterisation. The catheter can cause mucosal abrasion → inflammation → fibrosis → scarring → stricture formation. More common with larger catheters, difficult insertions, and long-term use |
| Clinical features | Subsequent difficulty with catheterisation, thin urinary stream, recurrent UTI, recurrent retention |
| Prevention | Use appropriate catheter size; use adequate lubrication (lignocaine jelly); gentle technique; minimise catheter duration; SPC for long-term drainage |
Since TURP is the definitive treatment for BPH-related AROU, its complications are essential exam knowledge.
Early complications of TURP: significant complications in ~15–20%, mortality in 0.2–2.5% [7]
| Complication | Mechanism / Details | Incidence |
|---|---|---|
| Bleeding | Prostatic venous sinuses are opened during resection → haemorrhage | 3–7% require transfusion [7] |
| Infection and urosepsis | Instrumentation of an infected/colonised urinary tract → bacteraemia | Variable |
| TUR syndrome ( < 1%) | Irrigation fluids used in TURP: ionic fluid cannot be used for monopolar → often used 1.5% glycine [7]. Fluid low in sodium enters venous channels → dilutional hyponatraemia + decreased osmolarity (aggravated by post-op stress-related ADH release) [7]. Lowest 1–2h after surgery, but slowly increases afterwards due to glycine uptake into cells [7]. S/S: N/V, confusion, hypertension, visual disturbance (flashing lights), giddiness, seizures [7]. Prevention: avoid non-conductive irrigants (use bipolar technique), monitor fluid absorbed (glycine deficit), limit operation time to < 1h, minimise irrigation pressure < 60 mmHg [7]. Management: stop OT immediately + Na replacement + Lasix [7] | < 1% [7] |
| Local injury | Incontinence (1%) [7]; strictures or bladder neck stenosis [7]; fistulation due to perforation of urethra or bladder dome [7] | Variable |
| Retrograde ejaculation | Incompetent bladder neck → retrograde flow of semen [7]; penile erection and sexual function rarely affected [7] | 40–60% [7] |
| Recurrence | Regrowth of prostatic tissue | 5% need re-operation in 5 years [7] |
Late complications of TURP [7]:
- Bladder neck stenosis and urethral strictures (7–8%)
- Urinary incontinence (2%): urge incontinence (early — detrusor irritability from surgery) / stress incontinence (late — sphincter damage)
- Regrowth of prostate
- Sexual dysfunction: ejaculatory dysfunction (especially retrograde ejaculation 40–60%); erectile dysfunction (5%): uncommon [7]
| Timing | Complication | Key Features |
|---|---|---|
| During retention (untreated) | UTI / urosepsis | Stagnant urine → bacterial proliferation |
| Bladder stones | Supersaturation + stasis + infection | |
| Hydronephrosis / hydroureter | Back-pressure from distended bladder | |
| Obstructive uropathy / post-renal AKI | Bilateral hydronephrosis → ↓ GFR | |
| Detrusor decompensation | Overdistension → loss of actin-myosin overlap | |
| Overflow incontinence | Intravesical pressure exceeds outlet resistance intermittently | |
| Delirium (elderly) | Pain, discomfort, autonomic disturbance | |
| Autonomic dysreflexia (SCI T6+) | Uninhibited sympathetic storm from bladder distension | |
| Immediately post-catheterisation | Post-obstructive diuresis | Tubular damage + accumulated solute excretion → > 200 mL/h |
| Haemorrhage ex vacuo | Mucosal decompression bleeding | |
| Transient hypotension | Vasovagal + pelvic venous pooling | |
| Short-term catheterisation | CAUTI | Foreign body → biofilm → ascending infection |
| Urethral trauma / false passage | Traumatic insertion | |
| Long-term catheterisation | Urethral stricture | Chronic mucosal irritation → fibrosis |
| Bladder stones (catheter-related) | Catheter as nidus for crystal deposition | |
| SCC of bladder | Chronic irritation → squamous metaplasia → malignancy | |
| Post-TURP | TUR syndrome | Glycine absorption → dilutional hyponatraemia |
| Retrograde ejaculation | Bladder neck incompetence | |
| Bleeding, incontinence, stricture | Surgical trauma |
High Yield Summary
- Complications of retention (the disease itself): recurrent UTI, bladder calculi, hydroureter/hydronephrosis, renal impairment/ARF (obstructive uropathy) [1] — these are also the absolute indications for TURP
- Post-obstructive diuresis: > 200 mL/h × ≥ 2h; primarily a problem of chronic retention; due to accumulated solute excretion + tubular damage; manage with close I/O monitoring, replace ~1/2 of UO with oral fluids or IV NS; do NOT remove catheter
- Haemorrhage ex vacuo: transient haematuria from mucosal decompression; usually self-limiting
- Transient hypotension: vasovagal response + pelvic venous decompression → monitor vitals
- Long-term catheterisation risks: UTI/urosepsis, urethral stricture, stones, prostatitis, SCC of bladder — this is why CISC is preferred over indwelling catheters
- TUR syndrome ( < 1%): dilutional hyponatraemia + fluid overload + glycine toxicity from monopolar TURP; prevented by bipolar technique (saline irrigant), limiting OT time < 1h, keeping irrigation pressure < 60 mmHg
- Retrograde ejaculation after TURP: 40–60%; due to incompetent bladder neck; counsel patients before surgery
- Autonomic dysreflexia: life-threatening hypertension in SCI patients (T6+) triggered by bladder distension — immediate catheterisation is the treatment
- Detrusor decompensation from prolonged overdistension may be irreversible → patient may need lifelong CISC even after obstruction is relieved
- Overflow incontinence is paradoxical — patient appears to void (dribbles) but is actually in retention; always check for a palpable bladder / scan PVR
Active Recall - Complications of AROU
References
[1] Lecture slides: GC 180. Benign prostatic hyperplasia, bladder outlet obstruction and urinary retention.pdf (pp. 37, 46) [2] Senior notes: Ryan Ho Urogenital.pdf (pp. 168, 172, 177); Ryan Ho Fundamentals.pdf (pp. 351, 353) [3] Senior notes: felixlai.md (AROU treatment/complications section, BPH complications section) [4] Senior notes: maxim.md (AROU complications, TURP complications) [5] Senior notes: Ryan Ho Critical Care.pdf (p. 26 — AKI management and complications) [6] Senior notes: Ryan Ho Psychiatry.pdf (p. 74 — DELIRIUM mnemonic) [7] Senior notes: Ryan Ho Urogenital.pdf (pp. 172, 177); Ryan Ho Fundamentals.pdf (p. 353) — TURP complications, BPH complications
Urology Overview
Master summary table of all urological conditions — definition, etiology, pathophysiology, clinical features, diagnosis, management, and complications at a glance.
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