GC002 Is He Fit For Surgery - Pre-operative Assessment
Pre-operative assessment is a systematic evaluation of a patient's medical history, physical status, and risk factors to determine their fitness for surgery and optimize outcomes.
Pre-operative Assessment: "Is the Patient Fit for Surgery?"
The Big Idea: Before any surgery, you must answer one critical question: does this patient have enough physiological reserve to survive the combined stress of surgery AND anaesthesia, and recover afterwards? Pre-operative assessment is the systematic process of estimating that reserve, identifying modifiable risk factors, optimizing the patient, planning the anaesthetic, and communicating risk to the patient and the surgical team.
Learning Objectives (from the lecture): [1]
- Describe some of the physiological stresses experienced by the perioperative patient
- Describe interactions between surgery and coexisting diseases in the perioperative patient
- Explain the purposes and describe the major elements of a preoperative anaesthetic assessment
How this fits into clinical practice and exams: This lecture is foundational — it underpins every surgical scenario you will encounter. Whether the minicase is about cholecystectomy, thyroidectomy, AAA repair, or colorectal cancer, the examiner expects you to demonstrate that you understand pre-operative assessment. Past papers frequently ask "state pre-operative management of this patient" (e.g. 2021 Minicase Q10 [8], 2019 Minicase Q10 [7], 2022 Minicase Section 4 [9]). This lecture gives you the framework to answer all of them.
1. Why Does the Patient Need to Be Fit? — Physiological Stresses of Surgery
This is the conceptual foundation of the lecture. Surgery is a controlled injury. The body must mount a physiological response to that injury — and that response demands energy and organ reserve.
"Surgery can increase metabolic demands and/or reduce supply" [1]
| Stress Category | Mechanism | Why It Matters |
|---|---|---|
| Acute "sterile" inflammation (SIRS) | Tissue damage triggers cytokine release (IL-1, IL-6, TNF-α), complement activation, and neutrophil migration — identical to the inflammatory cascade in infection, but without bacteria | Even sterile surgery can produce a systemic inflammatory response; the bigger the surgery, the bigger the response |
| Metabolic and neuroendocrine disturbances | Fasting → depleted glycogen; stress hormones (cortisol, catecholamines, glucagon, GH) → catabolic state, hyperglycaemia, protein breakdown | The body shifts to catabolism; diabetics lose control; malnourished patients deteriorate |
| Intraoperative perturbances | Bleeding → hypovolaemia; haemodynamic instability from manipulation near great vessels; changes to respiratory mechanics (e.g. pneumoperitoneum, lateral positioning, one-lung ventilation) | These demand real-time compensation — the heart must increase output, lungs must maintain gas exchange |
| Post-operative demands | Wound healing (needs protein, calories, oxygen); pain (increases metabolic rate, tachycardia); potential infection | Recovery is metabolically expensive; if organs can't keep up, complications ensue |
"In general, the larger amount of tissue damage, the greater the metabolic response" [1]
| Factor | Example | Clinical Implication |
|---|---|---|
| Anatomical location | Heart and large blood vessels → gross haemodynamic disturbances; operations on the lung → impaired ventilation | Cardiac surgery has the highest perioperative risk; lung resection reduces respiratory reserve permanently |
| Type of tissues involved | Operations on infected tissue → post-operative sepsis | An abscess drainage has different risk than a clean hernia repair, even if the surgical wound size is similar |
| Extent of tissue damage | Laparoscopic cholecystectomy vs. open hepatectomy | MIS → less tissue trauma → less SIRS → faster recovery (this connects to ERAS / minimally invasive surgery lectures) |
First Principles
Think of fitness for surgery as a supply-demand equation. Surgery INCREASES demand (metabolic stress, wound healing, fighting infection). Anaesthesia may temporarily DECREASE supply (cardiac output ↓, ventilation ↓, drug metabolism altered). The patient must have enough reserve in their organs to bridge this gap. If their baseline organ function is already borderline, the perioperative period may tip them into organ failure.
2. Anaesthesia — Both Ally and Threat
"Anaesthesia can actually alleviate stress — apart from several moments during induction and emergence (e.g. airway instrumentation)" [1]
This is an important nuance. General anaesthesia abolishes the pain response, blunts the neuroendocrine stress response (less catecholamine surge), and provides muscle relaxation for surgical access. Without anaesthesia, the stress of surgery would be far greater. However, the drugs used have their own physiological costs.
"Aspects of general anaesthetic can temporarily reduce the performance of different physiological functions. Depending on the patient's starting point for the relevant system, it could tip the patient over the edge into organ failure." [1]
This is the key concept: it's about the starting point. A patient with normal lungs can tolerate the respiratory depression of anaesthesia without issue. A patient with severe COPD (FEV1 30% predicted) may not be able to be weaned off the ventilator post-operatively.
"Best to get the patient into the best shape as possible — 'optimization'" [1]
3. How Anaesthesia Affects Each Organ System (and How Co-existing Disease Amplifies Risk)
Anaesthetic agents may adversely affect the respiratory system at every level: [1]
- Central control: ↓ response to CO₂ and hypoxia
- Airway: reduce protective reflexes; ↑ work of breathing (resistance from breathing circuit), retained secretions, bronchospasm
- Lung mechanics: ↓ lung volumes, ↑ work of breathing; residual paralysis
- Gas exchange: ↑ V/Q mismatch
Why each matters from first principles:
| Effect | Mechanism | Clinical Consequence |
|---|---|---|
| ↓ CO₂/hypoxia response | Opioids and volatile agents depress the brainstem respiratory centres → the normal drive to breathe when CO₂ rises or O₂ drops is blunted | Post-op hypoventilation, especially dangerous in COPD patients who already rely on hypoxic drive |
| Reduced protective reflexes | Laryngeal and cough reflexes suppressed → secretions and gastric contents not cleared | Aspiration risk, particularly during induction and emergence |
| ↓ Lung volumes | Supine position + abdominal contents pushing diaphragm cephalad + muscle relaxants → functional residual capacity (FRC) falls → small airways close → atelectasis | Postoperative atelectasis is the most common pulmonary complication |
| ↑ V/Q mismatch | Atelectatic lung still perfused but not ventilated → shunt; paralysed diaphragm + position → ventilation redistributed | Hypoxaemia intra- and post-operatively |
| Residual paralysis | Incomplete reversal of neuromuscular blocking agents | Upper airway obstruction, aspiration, hypoventilation in recovery |
Pre-existing pulmonary diseases increase respiratory complications: [1]
- Intraoperative: coughing on induction, laryngospasm, bronchospasm, desaturation
- Post-operative: mucous retention pneumonia, respiratory failure
Anaesthetic drugs affect cardiac performance: [1]
- Vasodilation
- Venodilation
- Chronotropy (↓ heart rate)
- Inotropy (↓ contractility) → Reduced cardiac output and tissue perfusion
Why this matters: Most anaesthetic agents (propofol, volatile agents) cause dose-dependent myocardial depression and vasodilation. The healthy heart compensates via baroreceptor reflexes. The diseased heart (e.g. severe LV dysfunction, aortic stenosis) cannot.
Surgical stress alters haemodynamics: [1]
- Increases metabolic demands (pain of surgery)
- Reduced tissue perfusion (reduced cardiac output ± reduced circulating volume from bleeding)
- May exacerbate myocardial ischaemia
Perioperative cardiac failure: [1]
- Inability of the heart to meet increased demand during surgery
- Increased metabolic demand
- May develop arrhythmias
- Fixed cardiac output states e.g. Aortic Stenosis
High Yield — Aortic Stenosis
Aortic stenosis is a "fixed cardiac output state" — the heart cannot increase output to meet demand because the valve obstruction limits flow. These patients are extremely high risk for perioperative hypotension and cardiac failure. They cannot compensate for the vasodilation caused by anaesthetic agents. This is a classic exam discriminator.
Hepatic Dysfunction in the perioperative period: [1]
- Reduced synthetic function → ↓ protein binding of drugs; impaired clotting
- Reduced metabolic function → ↓ drug metabolism and clearance; ↓ clearance of toxins → encephalopathy
- Circulatory disturbances → portal hypertension, ascites, high circulating volume → affects drug distribution
Why this matters from first principles:
- Many anaesthetic drugs are protein-bound (e.g. thiopental is ~85% albumin-bound). In hypoalbuminaemia, more free drug → exaggerated effect at lower doses → overdose risk.
- Coagulopathy (↓ clotting factors synthesized by liver) → bleeding risk during and after surgery.
- Altered volume of distribution (ascites = expanded extracellular fluid) → unpredictable drug pharmacokinetics.
- Hepatic encephalopathy can worsen post-operatively (from opioids, constipation, GI bleeding, infection).
Hepatic reserve assessment for hepatic resection (from supporting sources): Child-Pugh score, CT hepatic volumetry (≥30% FLR in normal liver, ≥40% in cirrhotic liver), ICG clearance (retention < 14% at 15 min for major hepatectomy) [5][6].
Renal dysfunction in the perioperative period: [1]
- Reduced drug excretion
- Electrolyte abnormalities
- Hypertension
- Severe anaemia
- Platelet dysfunction
Why this matters: Renally excreted drugs (e.g. morphine-6-glucuronide, certain antibiotics) accumulate → prolonged sedation, toxicity. Hyperkalaemia → arrhythmias under anaesthesia. Uraemic platelet dysfunction → bleeding. Anaemia → reduced oxygen-carrying capacity at a time when demand is increased.
Endocrine dysfunction in the perioperative period — Diabetes: [1]
- Associated CVS & renal problems
- Fasting and surgical stress upsets sugar control
- Diabetogenic hormones ↑ perioperatively (cortisol, glucagon, catecholamines, GH — all counter-regulatory to insulin)
- Both hyper and hypoglycaemia detrimental to CNS
Why fasting is particularly dangerous in diabetics: They take medications that lower blood sugar, but if they're fasting, there's no carbohydrate intake to balance the drug effect → hypoglycaemia. Conversely, the surgical stress hormones drive blood sugar up, and without their usual medications, they may become severely hyperglycaemic → hyperosmolar state, impaired wound healing, increased infection risk.
Anaesthesia and Co-Existing Diseases: [1]
- Diseased organs → adverse effects of anaesthetic drugs
- Systemic illness → altered pharmacokinetics and pharmacodynamics
- Drug interactions → between patient's medications and drugs administered
- Affects anaesthetic techniques → certain conditions contraindicate certain techniques
| Interaction | Example |
|---|---|
| Diseased organ → exaggerated drug effect | Cirrhotic liver → reduced metabolism of midazolam → prolonged sedation |
| Systemic illness → altered PK/PD | Renal failure → reduced clearance of morphine metabolites → respiratory depression |
| Drug interactions | Patient on MAO inhibitors → pethidine → serotonin syndrome (fatal) |
| Condition contraindicates technique | Patient on anticoagulants → neuraxial (spinal/epidural) anaesthesia contraindicated due to epidural haematoma risk |
Purpose of the pre-operative consultation: [1]
- Assessment of patient — Identification & optimization of co-morbidities
- Assessment of risk
- Plan anaesthetic & perioperative care → ? improvement in outcome
- Provide explanations & instructions to patients — what will happen? → Rapport & relieve anxiety
High Yield — Purposes of Pre-op Assessment
This is a commonly tested list. The four pillars are: (1) Assess the patient, (2) Stratify risk, (3) Plan the anaesthetic, (4) Counsel the patient. In exam answers, always mention optimization of reversible comorbidities — this is the actionable part that examiners reward.
Questions behind the questions: [1]
- What is the probability that the patient will survive the surgery?
- What is the probability that the patient will survive without complications?
- If complications occur, how bad will they be?
6. Pre-operative Assessment — The Elements
6.1 History
General history in the Preoperative Assessment: [1]
- Most parts could be performed by responsible medical officers
- Early identification can minimise delays or deferments to surgery
This means that as a junior doctor, YOU are expected to take the pre-op history. Don't wait for the anaesthetist to discover that the patient is on warfarin on the morning of surgery.
- Standard medical history: presenting complaint, HPC, PMH, drug history, allergy history, family history, social history (smoking, alcohol, occupation)
- Focus on systems that are most affected by surgery/anaesthesia: CVS, respiratory, hepatic, renal, endocrine
- Specifically ask about:
- Exercise tolerance (see METs below)
- Symptoms of undiagnosed cardiac/respiratory disease (chest pain, dyspnoea, orthopnoea, PND)
- Previous surgical/anaesthetic history
SHOULD ASCERTAIN A COMPLETE AND ACCURATE MEDICATION LIST OF ANY PATIENT SCHEDULED TO HAVE SURGERY!! [1]
This is in all-caps in the lecture for a reason. Medication errors around surgery are a major source of preventable harm.
Medication Lists: [1]
- Drugs that need to be stopped
- Drugs that should not be stopped (but may need different routes or suitable alternatives)
- Drugs that may need to be measured
- 'Recreational' drug use
- Oral contraceptives
Why oral contraceptives matter: Combined OCPs increase the risk of VTE. The British National Formulary recommends stopping combined OCPs 4 weeks before major elective surgery (especially if prolonged immobilization is expected). This is a classic exam point.
Why recreational drugs matter: Cocaine → recent use can cause perioperative hypertensive crisis, arrhythmias, coronary vasospasm. Chronic alcohol use → delirium tremens post-operatively, altered drug metabolism. Chronic opioid use → tolerance → higher analgesic requirements.
6.2 Medications That Must Be Stopped or Managed
Factors you need to alert your seniors or the anaesthesiologist: [1]
- Medications that need to be stopped or managed in consultation with specialists
- Implantable devices that need to be checked or functions altered
Anticoagulants: [1]
- "Traditional": e.g. Warfarin (approx. 3 to 4 days)
- "Novel" (NOACs): rivaroxaban (Xarelto), dabigatran (Pradaxa), apixaban (Eliquis), edoxaban (Lixiana)
| Drug | Class | Mechanism | Stop Before Surgery | Notes |
|---|---|---|---|---|
| Warfarin | Vitamin K antagonist | Inhibits factors II, VII, IX, X | 3–4 days | Check INR; may need bridging anticoagulation with LMWH if high thrombotic risk (e.g. mechanical heart valve, recent VTE) |
| Rivaroxaban | Direct factor Xa inhibitor | Directly inhibits factor Xa | Per formula (GFR, dose, surgery type); rule of thumb: 3–4 half-lives [2] | Shorter and more predictable offset than warfarin; renal excretion matters |
| Apixaban | Direct factor Xa inhibitor | Same as rivaroxaban | Same approach | Least renally excreted of the NOACs |
| Dabigatran | Direct thrombin inhibitor | Directly inhibits thrombin | Same approach; heavily renally excreted | Idarucizumab available as specific reversal agent |
| Edoxaban | Direct factor Xa inhibitor | Same as rivaroxaban | Same approach |
Antiplatelets: [1]
- ADP receptor inhibitors: Clopidogrel (Plavix)
Clopidogrel irreversibly inhibits the P2Y12 ADP receptor on platelets → the platelet is disabled for its entire 7–10 day lifespan. Therefore, clopidogrel must be stopped at least 5–7 days before surgery to allow enough new platelets to be produced.
Aspirin is often continued for minor surgery but stopped for neurosurgery, spinal surgery, and operations with very high bleeding risk. The decision depends on balancing thrombotic vs. bleeding risk (often a cardiology/surgery joint decision).
Bridging Anticoagulation
Bridging means substituting a short-acting anticoagulant (usually LMWH) while the long-acting one (warfarin) wears off, to protect high-risk patients (e.g. mechanical heart valve, recent DVT/PE) from thromboembolic events. Not all patients need bridging — low-risk AF patients on warfarin may simply stop and restart. This is a nuanced clinical decision that should involve specialists.
Diabetic medications: [1]
- SGLT2 inhibitors ("...gliflozins"): Empagliflozin (Jardiance), Dapagliflozin (Farxiga)
- SHOULD BE STOPPED 48 hours before surgery
- Insulin: regimes will need to be modified depending on fasting requirements
Why stop SGLT2 inhibitors? They cause euglycaemic diabetic ketoacidosis (euDKA) — a dangerous condition where the patient develops DKA with a normal or near-normal blood glucose. The mechanism: SGLT2 inhibitors cause glycosuria → lower blood glucose → lower insulin secretion → uninhibited lipolysis → ketogenesis. In the perioperative setting, fasting + surgical stress + SGLT2i = perfect storm for euDKA. Because the glucose is normal, it's easily missed. This is extremely high yield for exams.
Other diabetic medication adjustments (not explicitly in this lecture but commonly tested):
- Metformin: traditionally stopped 48h before surgery (concern for lactic acidosis, especially if renal impairment or contrast dye used); newer guidelines are less strict for minor surgery
- Sulfonylureas: omit on morning of surgery (risk of hypoglycaemia during fasting)
- Insulin: continue basal insulin at reduced dose; variable rate insulin infusion (VRII, "sliding scale") for the perioperative period if prolonged fasting
| Drug Class | Action Before Surgery | Reason |
|---|---|---|
| ACE inhibitors / ARBs | Often withheld on morning of surgery | Risk of refractory intraoperative hypotension (they block the RAAS, which is a key compensatory mechanism for anaesthesia-induced vasodilation) |
| Beta-blockers | Continue | Abrupt withdrawal → rebound tachycardia, hypertension, may precipitate MI |
| Statins | Continue | Pleiotropic anti-inflammatory effects may be beneficial perioperatively |
| Corticosteroids (chronic) | Continue and give stress dose | Chronic use → HPA axis suppression → cannot mount cortisol response to surgical stress → Addisonian crisis |
| MAO inhibitors | Complex — discuss with anaesthetist | Interaction with pethidine (serotonin syndrome), indirect sympathomimetics |
| Oral contraceptives | Stop 4 weeks before major surgery | ↑ VTE risk |
| HRT | Stop 4 weeks before major surgery | ↑ VTE risk |
| Lithium | Often continued with monitoring | Narrow therapeutic index; renal excretion affected by perioperative fluid shifts |
Devices: [1]
- Pacemakers and defibrillators → may require checking; certain functions may require disabling
- Prosthetic heart valves
- Deep brain stimulators
Why disable defibrillator function? Surgical diathermy (electrocautery) produces electromagnetic interference that the defibrillator may interpret as ventricular fibrillation → it will deliver an inappropriate shock to the patient on the operating table. The defibrillator's sensing function must be disabled pre-operatively, and external defibrillation pads must be applied as backup. [2]
Prosthetic heart valves: These patients are almost always on anticoagulation (mechanical valves → lifelong warfarin). This connects back to the anticoagulant management discussion — they will likely need bridging.
Anaesthetic History: [1]
- Any previous anaesthetic experiences
- Any known complications or difficulties:
- Difficult airway management
- Awareness (inadvertent recall of intraoperative events)
- Post-Operative Nausea and Vomiting (PONV)
- Delayed emergence from anaesthesia
- Genetic problems (rare): Pseudocholinesterase deficiency, Malignant Hyperthermia
- Nerve damage
| Complication | Why It Matters | What to Do |
|---|---|---|
| Difficult airway | If the patient has a known difficult airway, the anaesthetist must prepare alternative airway equipment, call for senior help, and potentially plan an awake fibreoptic intubation | Document clearly; alert anaesthetist early |
| Awareness | ~0.1–0.2% of GA patients have intraoperative recall; psychological trauma (PTSD) → use of BIS monitoring, appropriate anaesthetic depth | Previous awareness → anaesthetist will use additional monitoring |
| PONV | Some patients are highly susceptible (female, non-smoker, history of motion sickness, opioid use) → prophylactic antiemetics | Dexamethasone, ondansetron prophylaxis |
| Pseudocholinesterase deficiency | Suxamethonium normally hydrolyzed in < 5 min by pseudocholinesterase. Deficiency → prolonged paralysis (hours) → patient cannot breathe independently after surgery → needs ventilatory support [3] | Family history is important; prevalence ~1/2000 |
| Malignant Hyperthermia (MH) | Genetic defect in ryanodine receptor → uncontrolled intracellular Ca²⁺ release → muscle rigidity, massively ↑ metabolism, hyperthermia → fatal if untreated. Triggers: suxamethonium, all volatile agents EXCEPT nitrous oxide [3] | Family history; avoid triggers; have dantrolene available |
Malignant Hyperthermia — Exam Classic
MH is triggered by suxamethonium and ALL inhalational agents EXCEPT nitrous oxide. [1][3] The key signs are unexplained ↑ ETCO₂ (earliest sign), rigidity, tachycardia, and hyperthermia (a LATE sign). Treatment is dantrolene + active cooling + supportive care. Mortality is ~80% untreated, ~20% treated. Always ask family history before GA.
7. Physical Examination
Physical Examination: [1]
- Emphasize cardiorespiratory system
- Neurological examination when relevant:
- Those with history of CVA, neurological damage
- When contemplating regional anaesthesia
- Body parts relevant to the conduct of anaesthesia:
- Upper airway
- Spine
The airway exam is unique to pre-operative assessment and absolutely critical. Failure to anticipate a difficult airway is the leading cause of anaesthesia-related morbidity and mortality.
Key components:
- Mallampati classification (I–IV): patient opens mouth and protrudes tongue; assess visibility of posterior pharyngeal structures. Class III–IV → potentially difficult intubation
- Thyromental distance ( < 6.5 cm suggests difficult laryngoscopy)
- Mouth opening ( < 3 finger-breadths is concerning)
- Neck mobility (limited extension → difficult alignment of oral, pharyngeal, and laryngeal axes)
- Dentition (loose teeth, prominent upper incisors → risk of dental damage)
- Obesity / short neck / receding mandible → predict difficulty
- CVS: Blood pressure, heart rate and rhythm, murmurs (especially aortic stenosis — fixed output state!), JVP, peripheral oedema, signs of heart failure
- Respiratory: Respiratory rate, oxygen saturation, auscultation for wheeze/crackles, chest wall movement, accessory muscle use
- Document baseline before regional anaesthesia (spinal/epidural) so that any new deficit post-operatively can be identified
- Document baseline before surgery near nerves (e.g. thyroidectomy → recurrent laryngeal nerve → vocal cord function) [4]
Investigations: [1]
- Should only be undertaken with purpose:
- Helps with or changes management
- Confirm diagnosis
- Assess severity
- Document baseline if it is expected to shift in the perioperative period
- "Routine" or "screening" investigations are NOT indicated for the most part
This is a paradigm shift from the old practice of ordering "routine pre-op bloods and CXR on everyone." Modern evidence shows that blanket screening does not improve outcomes and may cause harm (false positives → unnecessary further investigation → delay surgery → patient anxiety).
8.1 When Are Specific Investigations Indicated?
| Investigation | Indication (purpose-driven) |
|---|---|
| FBC | Expected blood loss; known anaemia; renal disease; haematological disease; major surgery |
| U&E (Renal function) | Renal disease; medications affecting electrolytes (diuretics, ACEi, digoxin); major surgery; DM |
| LFT | Known liver disease; alcohol use; jaundice |
| Coagulation (PT/APTT) | Anticoagulant therapy; liver disease; bleeding history; major surgery |
| Blood glucose | Diabetes; on steroids |
| Group & Save / Crossmatch | Expected blood loss; transfusion anticipated |
| ECG | Known cardiac disease; symptoms; age > 65 (varies by guideline); DM; HTN |
| CXR | Acute cardiorespiratory symptoms; known unstable cardiorespiratory disease; NOT for age or smoking alone in absence of symptoms [10] |
| Pulmonary function tests | Known respiratory disease being optimized; lung resection surgery (see ppoFEV1 below) |
| Echocardiography | Suspected valvular disease, heart failure, to assess LV function before major surgery |
| Stress testing / CPET | To assess functional capacity when history is unreliable or METs < 4 |
CXR Is NOT Routine Pre-op
A past paper question asks which pre-operative patient should have a CXR indicated — the answer is the patient with acute heart failure, NOT "an old man undergoing cholecystectomy" or "a smoker" without acute symptoms. [10] "Routine" CXR for age or smoking history alone is not evidence-based.
9. Risk Stratification
American Society of Anesthesiologists (ASA) Classification System — in use for over 60 years. Used to assess and communicate a patient's pre-anesthesia medical co-morbidities. When used with other factors (e.g. type of surgery, frailty, level of deconditioning), it can be helpful in predicting perioperative risks. [1]
| ASA Class | Definition | Examples |
|---|---|---|
| I | A normally healthy individual | Healthy, non-smoker, minimal alcohol |
| II | A patient with mild systemic disease | Well-controlled DM, mild asthma, social drinker, BMI 30–40, current smoker |
| III | A patient with severe systemic disease that is not incapacitating | Poorly controlled DM, COPD, morbid obesity (BMI ≥ 40), stable angina, moderate-severe renal impairment, pacemaker |
| IV | A patient with incapacitating systemic disease that is a constant threat to life | Recent MI ( < 3 months), ongoing cardiac ischaemia, severe valve disease, sepsis, DIC, ESRD not on dialysis |
| V | A moribund patient who is not expected to survive 24 hours with or without surgery | Ruptured AAA, massive trauma, intracranial haemorrhage with mass effect |
| E suffix | Emergency operation | Added to any class (e.g. ASA IIIE) |
High Yield — ASA Classification
Memorize this table. It appears in MCQs and SAQs. Key points: ASA is about comorbidities, not about the surgery. ASA alone does not determine fitness — it must be combined with surgical risk, functional capacity, and frailty assessment.
Metabolic equivalents (METs) are multiples of the basal metabolic rate, assumed to be 3.5 mL·kg⁻¹·min⁻¹. [1]
In major non-cardiac surgery, the inability to climb 2 flights of stairs has a positive predictive value of 82% for postoperative pulmonary and cardiac complications or death within 30 days of surgery. Climbing 2 flights of stairs demands > 4 METs. [1]
| METs | Activity Examples | Clinical Significance |
|---|---|---|
| 1 | Eating, dressing, walking around the house | Baseline metabolic rate |
| 2–3 | Walking 2 blocks on level ground, light housework | Below the threshold for most surgery |
| 4 | Climbing 2 flights of stairs, walking up a hill, heavy housework | CRITICAL THRESHOLD — if patient can do this, they likely have adequate reserve for most non-cardiac surgery |
| 7–8 | Jogging, carrying heavy objects, moderate sport | Good reserve |
| > 10 | Vigorous sport (swimming, tennis, football) | Excellent reserve |
The 4-MET threshold (= 2 flights of stairs) is the key discriminator. [1][2]
From supporting notes: [3]
- Low risk of MACE ( < 1%): proceed to surgery
- High risk of MACE (≥1%): assess METs
- ≥4 METs: fit for GA
- < 4 METs: consider pharmacologic stress testing (thallium scan or stress cardiac MRI); coronary revascularization if abnormal
Exam Favourite — Climbing 2 Flights of Stairs
"The inability to climb 2 flights of stairs has a PPV of 82% for postoperative pulmonary/cardiac complications or death within 30 days." This specific statistic is directly from the lecture and is very likely to appear in MCQ or SAQ format. The threshold is 4 METs.
While the lecture focuses on patient factors, the type of surgery is equally important. Surgical risk is typically classified as:
| Risk Category | Examples | Estimated 30-day Cardiac Risk |
|---|---|---|
| Low risk | Endoscopy, superficial procedures, cataract, breast surgery | < 1% |
| Intermediate risk | Abdominal surgery, carotid endarterectomy, hip/knee replacement, head and neck surgery | 1–5% |
| High risk | Aortic and major vascular surgery, prolonged surgery with large fluid shifts/blood loss | > 5% |
"Risk assessment, NOT a prediction or guarantee" [1]
"…best estimate, based on available information, of the likelihood that the patient will be able to supply sufficient oxygen and nutrients to tissues in the perioperative period…" [1]
"Informs patient's decision making and perioperative management" [1]
"Should be made as a team between surgeons, anaesthesiologists and relevant specialists" [1]
10. Optimization of Comorbidities
Optimize patient as far as possible for elective patients. For emergency surgery… do the best you can with increased monitoring and post-operative care. [1]
This is a crucial distinction. Elective surgery gives you the luxury of time to optimize. Emergency surgery does not — but you still do what you can (even if it's 30 minutes of fluid resuscitation and antibiotics before a laparotomy for perforated viscus).
Indications for consulting other specialists: [1]
- Diagnosis and determining severity — "Is the chest pain of cardiac cause?"
- Optimization of the condition — "Are there reversible elements in the patient with COPD?"
- Management of the condition in the perioperative period — "Does the patient require bridging anticoagulation?"
Lung function should be optimized before general anaesthesia for elective surgery: [1]
- Stop smoking
- Treat infections
- Bronchodilators; steroids
Post-op care to reduce complications: [1]
- Supplemental oxygen
- Adequate pain relief (pain → splinting → poor ventilation → atelectasis → pneumonia)
- Post-op physiotherapy: pre-op patient education (teach incentive spirometry, deep breathing exercises BEFORE surgery so the patient knows what to do after)
- Consider post-op ventilator support (for very high-risk patients, plan elective ICU admission)
Smoking cessation: Ideally ≥8 weeks before surgery for full benefit (reduced sputum production, improved mucociliary clearance, reduced carboxyhaemoglobin). Even 24–48 hours provides some benefit (reduced CO levels, improved oxygen delivery).
Cardiovascular diseases: [1]
- Delineate cardiac risk
- Judicious investigations
- Optimize cardiac status: lifestyle changes, medications, valvular surgery, (revascularization)
- Appropriate post-op monitoring
- Effective post-operative pain relief
Key principles:
- Control hypertension (but don't delay surgery for mild-moderate HTN; severe HTN [SBP > 180 or DBP > 110] should be controlled)
- Optimize heart failure (diuretics, ACEi, beta-blockers)
- Continue beta-blockers and statins perioperatively
- For severe aortic stenosis → consider valve replacement/TAVI before elective non-cardiac surgery
- Revascularization (PCI/CABG) is rarely indicated solely to reduce perioperative risk — it's indicated if the patient would benefit from it regardless of the planned surgery
Liver: [1]
- Treat coagulopathy (vitamin K, FFP, cryoprecipitate if needed)
- Other supportive treatment
- Nutrition (many liver patients are malnourished → pre-op nutritional support)
- Adjust drug doses
Renal: [1]
- Consider prehydration (to protect against contrast nephropathy and perioperative AKI)
- Minimise nephrotoxins (NSAIDs, aminoglycosides, contrast dye — if needed, use with hydration)
Diabetes: [1]
- Clear fasting instructions & treatment plan
- Omit oral hypoglycaemic on morning of surgery
- May require an insulin dextrose infusion (VRII / "sliding scale")
- Meticulous perioperative sugar control
- Frequent monitoring
Target glucose range perioperatively: Generally 6–10 mmol/L (avoid both hypo and hyperglycaemia). Some centres aim for 6–12 mmol/L.
- Nutritional optimization (GC 185): Malnourished patients (albumin < 30, BMI < 18.5, unintentional weight loss > 10%) should receive pre-operative nutritional support (oral supplements, enteral feeding, or TPN if gut non-functional) for at least 7–14 days if surgery can be delayed [11]
- Anaemia correction (GC 155): Consider iron supplementation, EPO, or pre-operative transfusion if Hb critically low; patient blood management strategies to minimize need for transfusion [12]
- Frailty assessment (Frailty in Older Adults): Frailty is an independent predictor of post-operative complications, prolonged length of stay, and mortality — increasingly recognized as more important than age alone [13]
- Pre-operative vaccination: For splenectomy patients — pneumococcal, Haemophilus influenzae type B, meningococcal, and influenza vaccines, ideally 2 weeks before elective splenectomy [14]
Anaesthetic Plan: [1]
- Type of anaesthesia: General vs Regional or Combination
- Airway management
- Preparation: patient, staff, equipment and drugs & fluids
- Intraoperative management: Monitoring, positioning, fluid management
- Post-operative management: Analgesia, Disposition
| Component | Details |
|---|---|
| Type | GA (inhalational or TIVA); Regional (spinal, epidural, nerve block); Combination; Local + sedation |
| Airway | Facemask, LMA (supraglottic), endotracheal tube (ETT); plan for difficult airway |
| Preparation | Fasting status confirmed; IV access; consent; equipment check (AAGBI checklist); drugs drawn up; blood available if needed |
| Monitoring | Standard: ECG, SpO₂, NIBP, capnography, temperature. Extended: arterial line, CVP, cardiac output, BIS |
| Positioning | Supine, lateral, prone, lithotomy — each has specific risks (nerve injury, pressure sores, airway access) |
| Fluids | Maintenance, replacement, resuscitation — guided by clinical assessment and monitoring |
| Analgesia | Multimodal: paracetamol, NSAIDs (if no contraindication), opioids, regional techniques, local infiltration |
| Disposition | Recovery room → ward vs. HDU vs. ICU — determined by patient risk and surgery type |
From supporting lecture material [15], the decision to operate depends on three factors:
| Factor | Key Questions |
|---|---|
| Disease factor | Staging? Operable? Life-saving vs. functional vs. QOL surgery? Can it be managed conservatively? |
| Patient factor | Fit enough? Parameters that can be optimized? Does the patient want surgery? Social support? |
| Surgeon factor | Expertise available? |
Assessing fitness for surgery: [1] "Should be made as a team between surgeons, anaesthesiologists and relevant specialists"
Anaesthesiologists can then determine: [1]
- Estimate whether there is sufficient reserve for surgery:
- Meet increased metabolic demands from the stress of surgery and for healing
- As there may also be some compromise in cardiorespiratory function from anaesthesia
- Estimate the risk of exacerbating certain comorbidities:
- Ischaemic heart disease
- Respiratory failure
14. Exam Intelligence
| Paper | Question Type | Topic |
|---|---|---|
| 2021 Minicase Q10 [8] | SAQ | "State pre-operative management of this patient" (cholecystitis case) |
| 2019 Minicase Q10 [7] | SAQ | "Name two pre-operative management approaches and justify with reason" |
| 2022 Minicase Section 4 [9] | SAQ | Post-thyroidectomy complications (requires pre-op assessment knowledge: vocal cord function, calcium baseline) |
| 2020 MCQ Q70 [16] | MCQ | AAA management — involves assessment of fitness (age, comorbidities, functional status) |
| 2025 MCQ Q59 [17] | MCQ | Remifentanil would NOT be useful for post-op pain (ultra-short acting, offset too fast — connects to anaesthetic planning) |
| Trap | Correct Approach |
|---|---|
| "Routine pre-op investigations for everyone" | Investigations should be purpose-driven, not routine |
| Confusing ASA with surgical risk | ASA describes PATIENT comorbidities only; combine with surgical risk for overall assessment |
| Forgetting SGLT2 inhibitor cessation | Stop 48 hours before surgery — euglycaemic DKA |
| Stopping beta-blockers pre-op | Continue — withdrawal is dangerous |
| Ordering CXR for "old age" or "smoking" | Only indicated for acute/unstable cardiorespiratory disease |
| Ignoring airway assessment | A "can't intubate, can't oxygenate" scenario is the most feared anaesthetic emergency |
| Not mentioning optimization in pre-op SAQ answers | Always state what you would optimize (e.g., "stop smoking, treat chest infection, optimize bronchodilators") |
"Pre-operative management" SAQ template:
- Assess — full history and examination including comorbidities, medications, functional capacity, airway
- Investigate — guided by clinical findings (blood tests, ECG, imaging as indicated)
- Optimize — stop/modify medications (anticoagulants, SGLT2i, OHA), treat reversible conditions (infection, bronchospasm, anaemia, dehydration), nutritional support if malnourished
- Risk stratify — ASA class, METs, surgical risk category
- Plan — anaesthetic plan (GA vs regional), monitoring level, post-op disposition (ward/HDU/ICU)
- Consent and counsel — explain procedure, risks, what to expect, fasting instructions
- Specific measures — e.g., for thyroidectomy: document vocal cord function, pre-op calcium; for splenectomy: vaccinations; for diabetic: insulin-dextrose infusion plan
-
"List the purposes of pre-operative assessment." → Assessment of patient + identification & optimization of comorbidities; risk assessment; planning anaesthetic and perioperative care; patient counselling and rapport.
-
"A 65-year-old diabetic man on empagliflozin, clopidogrel, and atenolol is scheduled for elective laparoscopic cholecystectomy. What medications need to be stopped or modified pre-operatively?" → Empagliflozin: stop 48h before (risk of euDKA). Clopidogrel: stop 5–7 days before (irreversible platelet inhibition). Atenolol: CONTINUE (withdrawal → rebound HTN, tachycardia, MI risk). Oral hypoglycaemics: omit on morning of surgery; may need insulin-dextrose infusion.
-
"Describe the ASA classification system." → Five classes from I (healthy) to V (moribund, not expected to survive 24h); E suffix for emergency.
-
"What functional capacity assessment predicts perioperative complications?" → Inability to climb 2 flights of stairs ( > 4 METs) has a PPV of 82% for postoperative pulmonary/cardiac complications or death within 30 days.
-
"How does general anaesthesia affect the respiratory system?" → Central: ↓ response to CO₂ and hypoxia. Airway: ↓ protective reflexes, ↑ WOB, retained secretions. Lung mechanics: ↓ lung volumes, residual paralysis. Gas exchange: ↑ V/Q mismatch.
-
"Why is aortic stenosis particularly dangerous perioperatively?" → Fixed cardiac output state — cannot increase output to compensate for anaesthesia-induced vasodilation or surgical stress → severe hypotension, myocardial ischaemia, cardiac failure.
-
"A patient with severe COPD is planned for major abdominal surgery. What pre-operative and post-operative measures would you implement?" → Pre-op: stop smoking, treat infections, optimize bronchodilators/steroids, pre-op physiotherapy education, lung function testing, consider HDU/ICU booking. Post-op: supplemental O₂, adequate analgesia (to prevent splinting), chest physiotherapy, incentive spirometry, monitor for respiratory failure, consider post-op ventilator support.
High Yield Summary
Pre-operative assessment is about answering: "Does this patient have enough reserve to survive the combined stress of surgery and anaesthesia?" The systematic approach is:
- History — comorbidities, medications (stop anticoagulants/SGLT2i; continue beta-blockers), anaesthetic history (difficult airway, MH, pseudocholinesterase deficiency), functional capacity (4 METs / 2 flights of stairs = threshold)
- Examination — CVS, respiratory, airway, neurological (if regional planned)
- Investigations — purpose-driven, NOT routine
- Risk stratification — ASA classification (I–V + E), METs, surgical risk category
- Optimization — treat reversible conditions, adjust medications, nutritional support, specialist input
- Anaesthetic plan — type, airway, monitoring, fluids, analgesia, disposition
- Consent and counselling — inform, build rapport, relieve anxiety
Key exam points: SGLT2i stop 48h (euDKA risk), warfarin stop 3–4 days (consider bridging), clopidogrel stop 5–7 days, climbing 2 flights of stairs = 4 METs (PPV 82%), aortic stenosis = fixed output state, investigations only with purpose, ASA class ≠ surgical risk.
Active Recall - Pre-operative Assessment
[1] Lecture slides: GC 002 - Is he fit for surgery - Pre-operative assessment.pdf (all pages) [2] Senior notes: Gen Clerk Anaes + Microbiology Summary.pdf (p2–3) [3] Senior notes: Maksim Surgery Notes.pdf (p285, perioperative issues section) [4] Senior notes: Ryan Ho Endocrine.pdf (p22, pre-op preparation for thyroidectomy) [5] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p489, hepatic resection perioperative assessment) [6] Senior notes: Ryan Ho GI.pdf (p267, pre-operative assessment of operability for liver) [7] Past papers: 2019 Fourth Summative Mini Case.pdf (p13, Case 2 Q10) [8] Past papers: 2021 Fourth Summative Minicase.pdf (p19, Case 2 Q10) [9] Past papers: 2022 Fourth Summative Minicase.pdf (p10–12, Case 2 Section 3–4) [10] Senior notes: Ryan Ho Radiology.pdf (p8, pre-operative CXR question) [11] Lecture slides: GC 185. Feed him up before surgery Surgical nutrition, Enteral and parenteral feeding.pdf [12] Lecture slides: GC 155. Is blood transfusion absolutely required in patient management nowadays.pdf [13] Frailty in Older Adults - Kim DH 2024 (NEJM).pdf [14] Senior notes: Block A - Splenomegaly_ common causes of splenomegaly; myeloproliferative diseases.pdf (p20) [15] Lecture slides: 2022 07 29 Surgery Surgical Principles (Dr IYH Wong).pdf (p26) [16] Past papers: 2020 Fourth Summative Assessment MCQ paper.pdf (p27, Q70) [17] Past papers: 2025 Fourth Summative MCQ.pdf (p23, Q59)
GC001 How Would You Anaesthetise Me - Pharmacology Of Anaesthetic Drugs
The pharmacology of anaesthetic drugs encompasses the mechanisms of action, pharmacokinetics, and pharmacodynamics of intravenous induction agents, inhalational anaesthetics, neuromuscular blocking agents, opioids, and local anaesthetics used to achieve the triad of unconsciousness, analgesia, and muscle relaxation during general anaesthesia.
GC004 The Pain Is Intolerable - Pain Control
Pain control is the systematic assessment and management of acute or chronic pain using pharmacological, interventional, and non-pharmacological strategies to reduce suffering and restore function.