Pneumothorax is the presence of air in the pleural space, leading to partial or complete lung collapse.

Exam domain	One-glance essentials
Definition / diagnosis	Air in the pleural space causing partial or complete lung collapse ^[1] Primary, secondary, traumatic and tension forms differ ^[1]
Epidemiology / risks	Smoking is the strongest modifiable risk for primary spontaneous pneumothorax ^[1] COPD, cystic lung disease and positive-pressure ventilation increase risk ^[1]
Core mechanism	Ruptured subpleural bleb or diseased lung leaks air ^[1] A one-way valve creates tension with mediastinal pressure and obstructive shock ^[1]
Clinical picture	Sudden unilateral pleuritic pain and dyspnoea with reduced breath sounds ^[1] Hypotension, severe distress and deteriorating ventilation suggest tension ^[1]
Investigations	Stable patients: CXR or ultrasound confirms diagnosis ^[2] Do not image before treating clinically evident tension pneumothorax ^[2]
Management	Tension: immediate decompression followed by chest drainage ^[3] Stable treatment ranges from observation/aspiration to drain and definitive pleurodesis/surgery ^[3]
Complications	Tension physiology, respiratory failure and recurrence ^[4] Persistent air leak and re-expansion oedema may occur ^[4]
Prevention / follow-up	Smoking cessation markedly reduces recurrence ^[3] Avoid flying until radiographic resolution and specialist clearance; diving needs definitive advice ^[3]
Exam traps	*Do not wait for tracheal deviation—it is a late sign* ^[2] A small pneumothorax can be dangerous in severe underlying lung disease ^[3]

References

^[1] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155)

^[2] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155)

^[3] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155)

^[4] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155)

Pneumothorax

Pneumothorax (PTX) literally breaks down from Greek roots: "pneumo" = air, "thorax" = chest. It is defined as the presence of air in the pleural space ^[1]^[2]. Normally, the pleural space contains only a thin film (~5–15 mL) of serous fluid between the visceral and parietal pleurae, maintained at a sub-atmospheric (negative) pressure of approximately −3 to −5 cmH₂O at rest. When air enters this space, the negative pressure is lost, the elastic recoil of the lung causes it to collapse, and gas exchange is impaired.

The key concept is understanding why the lung stays inflated in the first place: the intrapleural pressure is negative relative to atmospheric pressure (thanks to the opposing elastic recoil forces of the lung inward and chest wall outward). Once air breaches either the visceral pleura (from inside) or the parietal pleura (from outside), the pressure gradient is lost, and the lung retracts toward its hilum.

Core Concept

The lung is a passive elastic structure held open by the negative intrapleural pressure. Any communication between the atmosphere and the pleural space — whether from the airway side (visceral pleura breach) or the chest wall side (parietal pleura breach) — will collapse the lung. The clinical severity depends on how much air accumulates and whether pressure continues to build (tension physiology).

2. Epidemiology

Primary spontaneous pneumothorax (PSP): incidence of approximately 7–18 per 100,000 per year in males and 1–6 per 100,000 per year in females ^[1]^[2]
Secondary spontaneous pneumothorax (SSP): incidence of approximately 6 per 100,000 per year in males, 2 per 100,000 per year in females
Traumatic and iatrogenic pneumothorax: variable depending on hospital practice and trauma burden

PSP: predominantly tall, thin, young males — typically aged 15–35 years ^[2]
- Male-to-female ratio: 3–6 : 1 ^[1]
- Why tall and thin? Taller individuals have a greater transpulmonary pressure gradient from apex to base (the alveolar pressure at the apex is relatively higher compared to intrapleural pressure because of gravitational effects on pleural pressure). This promotes development of subpleural blebs at the apex that can rupture.
SSP: older patients (typically > 50 years), reflecting the age distribution of COPD and other chronic lung diseases ^[1]

COPD is very common in Hong Kong (accounts for ~10% of public medical bed days ^[3]), making SSP secondary to COPD a significant burden
Smoking remains the dominant modifiable risk factor for both PSP and SSP ^[1]^[2]
Tuberculosis (TB) is still endemic in Hong Kong and is a recognized cause of SSP ^[1]
Iatrogenic pneumothorax occurs in the context of frequent use of central venous catheters and invasive procedures in Hong Kong's tertiary hospitals

Category	Risk Factors	Mechanism
Demographic	Male sex, tall stature, thin body habitus, age 15–35 (PSP), age > 60 (SSP recurrence)	Greater apical transpulmonary pressure gradient in tall individuals; male predominance unclear but possibly hormonal/connective tissue differences
Smoking	Dose-dependent (up to 20× risk in heavy smokers vs non-smokers)	Causes inflammatory small airway disease → air trapping → subpleural bleb formation; also impairs pleural mesothelial integrity
Previous PTX	Risk of recurrence 10–30% at 1–5 years (1st PSP), 50% at 3 years (SSP) ^[1]	Persistence of underlying pathology (blebs, bullae, pores of Kohn dilatation)
Pre-existing lung disease	COPD, TB, CF, asthma, CA lung, PCP, interstitial lung disease	Weakened alveolar walls, bullae formation, cavities communicating with pleural space
Subpleural blebs	Present in up to 90% of PSP patients on CT	Thin-walled air-containing spaces at lung apex that can rupture
Connective tissue disorders	Marfan syndrome, Ehlers-Danlos, homocystinuria	Defective collagen/connective tissue → weakened visceral pleura
Specific rare conditions	Lymphangioleiomyomatosis (LAM, young F), Langerhans cell histiocytosis (LCH, young M) ^[2]	LAM: smooth muscle proliferation in airways and lymphatics → cyst formation → rupture; LCH: granulomatous destruction → cysts
Birt-Hogg-Dubé syndrome	Autosomal dominant (FLCN gene mutation)	Lung cysts (especially basilar) predisposing to spontaneous PTX ^[5]
Iatrogenic	CVC insertion, mechanical ventilation (barotrauma), transthoracic lung biopsy, thoracocentesis, pleural biopsy, transbronchial biopsy ^[1]^[2]	Direct pleural puncture or positive-pressure-induced alveolar rupture
Trauma	Penetrating (stab, gunshot), blunt (rib fractures), blast injury ^[4]^[6]	Direct pleural space violation or rib fragment laceration of visceral pleura
Catamenial	Menstruating women, endometriosis	Ectopic endometrial tissue on diaphragm/pleura → tissue breakdown during menstruation → air entry; or air passage through diaphragmatic fenestrations from pneumoperitoneum

High Yield - Exam Favourite

When asked about risk factors for pneumothorax, always structure your answer: Patient factors (tall, thin, male, smoking, family history) → Lung disease (COPD, TB, CF, LAM, LCH) → Iatrogenic (CVC, ventilation, biopsy) → Trauma (penetrating, blunt, blast). Don't forget catamenial pneumothorax — a favourite viva question.

4. Anatomy and Function of the Pleural Space

Parietal pleura: lines the inner surface of the chest wall, mediastinum, and diaphragm. Supplied by intercostal arteries and innervated by intercostal nerves (somatic — this is why parietal pleural inflammation causes sharp, well-localized pain) and the phrenic nerve (diaphragmatic portion — referred shoulder tip pain).
Visceral pleura: intimately covers the lung parenchyma and extends into the fissures. Supplied by bronchial arteries. Has no somatic innervation — this is why visceral pleural pathology alone does not cause pain.
Pleural space: a potential space between the two layers containing ~5–15 mL of serous fluid. Functions as a lubricant and transmits the negative pressure that keeps the lung inflated.

At rest (FRC): intrapleural pressure ≈ −5 cmH₂O
During inspiration: becomes more negative (≈ −8 cmH₂O) → draws air into lungs
The lung's elastic recoil pulls it inward; the chest wall's elastic recoil pulls outward → the net effect is a negative intrapleural pressure
Gravity creates a vertical gradient: intrapleural pressure is more negative at the apex (≈ −8 cmH₂O) and less negative at the base (≈ −2 cmH₂O). Therefore, apical alveoli are more distended at rest and under greater transpulmonary pressure — explaining why blebs form preferentially at the apex and why PSP typically begins at the lung apex.

Under normal conditions, pleural capillary blood has a total gas pressure (sum of partial pressures of O₂, CO₂, N₂, H₂O) that is lower than atmospheric pressure by about 54 mmHg (the "tissue gas tension deficit")
This gradient drives absorption of air from the pleural space back into the blood at a rate of approximately 1.25% of hemithorax volume per day for air (which is 79% N₂)
O₂ is easier to absorb than N₂ — this is why supplemental O₂ therapy accelerates pneumothorax resolution: by replacing alveolar N₂ with O₂, the N₂ partial pressure in capillary blood drops, creating a steeper gradient for N₂ absorption from the pleural space ^[2]

Why Does O₂ Speed Up Pneumothorax Resolution?

Air in the pleural space is mostly N₂ (~79%). N₂ is poorly soluble and slowly reabsorbed. By giving high-flow O₂, you "nitrogen-wash" the blood — reducing blood PN₂ → steeper diffusion gradient → N₂ moves out of the pleural space into blood 4–6× faster. This can increase the reabsorption rate from ~1.25% to ~6% of hemithorax volume per day. However, avoid HFNC or NIPPV as these deliver positive pressure that may worsen the pneumothorax ^[2].

Safe triangle for chest drain insertion: bordered anteriorly by the lateral edge of pectoralis major, posteriorly by the lateral edge of latissimus dorsi, inferiorly by the 5th intercostal space, and superiorly by the axilla. Insertion is at the 4th or 5th intercostal space in the mid-axillary line.
2nd intercostal space, mid-clavicular line: site for needle decompression of tension pneumothorax and sometimes needle aspiration
Always insert just above the rib (to avoid the intercostal neurovascular bundle running in the costal groove along the inferior border of each rib)

5. Etiology (with Focus on Hong Kong)

5.1 Spontaneous Pneumothorax

Pathophysiology: Despite the label "no underlying lung disease," nearly all PSP patients have subclinical pathology. High-resolution CT shows subpleural blebs or bullae (small air-containing spaces, usually < 1–2 cm) at the lung apices in up to 90% of PSP patients. These blebs form due to:
1. Degradation of elastic fibres in visceral pleura (possibly related to smoking-induced inflammation or congenital weakness)
2. Increased mechanical stress at the apex (gravity-dependent transpulmonary pressure gradient)
3. Possible role of pleural porosity — microscopic holes in the visceral pleura allowing air leak even without visible blebs
Blebs rupture → air enters pleural space → lung collapses
Hong Kong relevance: Smoking is the most important modifiable risk factor. Despite public health campaigns, smoking prevalence remains ~10% in HK (higher in males). PSP classically presents in young men in their 20s.

Cause	Hong Kong Relevance	Pathophysiology
COPD (50–70% of SSP)	Very common in HK; accounts for 10% of public medical bed days ^[3]	Emphysematous bullae rupture; inflammatory weakening of alveolar walls; air trapping → overdistension
TB	Endemic in HK (incidence ~60/100,000)	Cavitary disease communicates with pleural space; pleuritis causes pleural weakening; caseous necrosis erodes visceral pleura
CA lung	Common in HK (leading cause of cancer death)	Tumour necrosis creates cavitation; tumour erodes visceral pleura; post-chemotherapy tumour regression
PCP infection (Pneumocystis jirovecii)	Seen in HIV+ patients	Creates thin-walled cysts (pneumatoceles) in lung parenchyma that rupture
Langerhans cell histiocytosis (LCH) — young males	Rare but high-yield	Granulomatous inflammation → cystic destruction of lung parenchyma → cyst rupture
Lymphangioleiomyomatosis (LAM) — young females	Rare but high-yield	Proliferation of abnormal smooth muscle cells → airway obstruction → cyst formation → rupture; associated with tuberous sclerosis
Cystic fibrosis	Less common in Chinese/HK population	Mucus plugging → air trapping → subpleural cyst formation → rupture
Asthma	Common in HK	Severe air trapping → alveolar overdistension → rupture (rare)
Interstitial lung disease (e.g., IPF)	Increasing recognition	Honeycombing creates subpleural cysts that can rupture
Birt-Hogg-Dubé syndrome	Rare	Basilar lung cysts (FLCN gene mutation) → spontaneous PTX ^[5]

Clinical Pearl

SSP usually presents earlier and more severe than PSP because patients have less respiratory reserve ^[1]. A 2 cm pneumothorax in a young healthy person may cause mild breathlessness; the same size in a COPD patient can cause respiratory failure. This is why the management thresholds differ (SSP: intervene at ≥ 1 cm; PSP: intervene at ≥ 2 cm) ^[2].

5.2 Traumatic Pneumothorax

Stabbing, chopping wounds (relevant to HK — "Chopped and stabbed wound in gang fight" ^[6])
Gunshot wounds (less common in HK)
Pathophysiology: Direct violation of parietal pleura (and sometimes visceral pleura) → atmospheric air enters pleural space. If the wound remains open ("sucking chest wound"), an open pneumothorax develops where air moves freely in and out.

"Hit by a van" scenario ^[4]^[7] — motor vehicle accidents, falls, assaults
Pathophysiology:
- Rib fractures → fractured rib ends lacerate visceral pleura and lung parenchyma
- Sudden compression → transient ↑ alveolar pressure → alveolar rupture (even without rib fractures)
- Deceleration injury → shearing of lung from hilum

Primary blast wave causes rapid pressure changes → alveolar rupture
Secondary (projectile fragments) and tertiary (body thrown) mechanisms can also cause PTX

Procedure	Mechanism
Central venous catheter (CVC) insertion — especially subclavian and IJV	Needle punctures lung apex/parietal pleura
Mechanical ventilation (barotrauma)	Positive pressure ventilation → alveolar overdistension → rupture → air tracks along perivascular sheaths to mediastinum → ruptures into pleural space (Macklin effect)
Transthoracic lung biopsy	Needle traverses pleura
Thoracocentesis / pleural biopsy / chest drain	Inadvertent lung puncture or air entry
Transbronchial lung biopsy	Forceps tears visceral pleura
Tracheostomy	Paratracheal dissection may enter pleural dome
Oesophageal atresia surgery / diaphragmatic hernia repair ^[8]	Neonatal thoracic surgery — operative pleural breach
Positive pressure ventilation in neonates ^[8]	Immature lungs prone to barotrauma

Iatrogenic PTX After CVC

Always order a post-procedure CXR after CVC insertion to check for pneumothorax and confirm catheter tip position. This is a classic exam scenario. The CXR also rules out haemothorax and hydrothorax ^[9].

6. Classification

Type	Mechanism	Pleural Pressure	Key Feature
Closed	Airway-pleural communication sealed as lung deflates; does not re-open	Negative	Spontaneous reabsorption over days to weeks ^[1]
Open	Communication remains continuously patent	Atmospheric	Bronchopulmonary fistula (e.g., ruptured emphysematous bulla, TB cavity, lung abscess into pleural space) ^[1]; or open chest wound ("sucking chest wound")
Tension	One-way valve → progressive accumulation of air within pleural space	Positive	Mediastinal shift → compress contralateral lung + impair systemic venous return → obstructive shock with cardiopulmonary collapse ^[1]^[2]

Size	Definition on Erect PA CXR
Small	< 2 cm interpleural distance at the level of the hilum (between lung edge and chest wall)
Large	≥ 2 cm interpleural distance at the level of the hilum

% pneumothorax = (1 − [average lung diameter³ / average hemithorax diameter³]) × 100% ^[2]
1 cm on PA CXR ≈ 27% of hemithorax volume ^[2]

Note: The ACCP uses 3 cm at the apex as the dividing line; BTS uses 2 cm at the hilum. HKU/HK generally follows BTS guidelines.

7. Pathophysiology (Detailed)

Breach in pleura → air enters pleural space → intrapleural pressure rises toward atmospheric
Loss of negative intrapleural pressure → the transpulmonary pressure (alveolar pressure minus intrapleural pressure) decreases → lung elastic recoil is no longer opposed → lung collapses
The degree of collapse depends on:
- Volume of air entering
- Whether the communication seals (closed), remains open, or acts as a one-way valve (tension)
- Compliance of the lung (stiff fibrotic lungs collapse less; compliant emphysematous lungs collapse more easily)

Consequence	Mechanism
Hypoxaemia	V/Q mismatch: collapsed lung is perfused but not ventilated (intrapulmonary shunt). Compensated partially by hypoxic pulmonary vasoconstriction (HPV) redirecting blood to the ventilated lung
Hypercarbia (usually mild in PSP)	Dead space ventilation in the collapsed lung; usually compensated by the contralateral lung unless bilateral PTX, tension, or SSP
Increased work of breathing	Reduced total ventilating lung volume → tachypnoea to maintain minute ventilation
Mediastinal shift (tension PTX)	Progressive air accumulation → positive pressure → pushes mediastinum to contralateral side
Impaired venous return (tension PTX)	Build-up of pressure → compress IVC → ↓ venous return → obstructive shock ^[2]
Contralateral lung compression (tension PTX)	Shifted mediastinum compresses the opposite lung → bilateral ventilatory failure
V/Q mismatch (tension PTX)	Combined effect of collapsed ipsilateral lung and compressed contralateral lung ^[2]

Pathophysiology:

A one-way valve mechanism develops — air enters the pleural space during inspiration but cannot escape during expiration
With each breath, more air accumulates → intrapleural pressure becomes progressively positive
Consequences:
- Compress IVC → ↓ venous return → obstructive shock ^[2]
- Mediastinal shift → kinking of great vessels → further ↓ cardiac output
- Compression of contralateral lung → bilateral respiratory failure
- V/Q mismatch — both lungs affected ^[2]

This is a clinical diagnosis. You should NOT wait for a CXR to diagnose tension pneumothorax — it is an emergency requiring immediate needle decompression. ^[1]

Tension Pneumothorax is a CLINICAL Diagnosis

Tension pneumothorax is a clinical diagnosis ^[1]. Never delay treatment to obtain a CXR. If a trauma patient has unilateral absent breath sounds, hyperresonance, tracheal deviation away from the affected side, distended neck veins, and hypotension — decompress immediately with a 14G needle at the 2nd ICS mid-clavicular line (or 4th/5th ICS mid-axillary line per newer ATLS guidelines), followed by chest drain insertion.

8. Clinical Features

Symptom	Frequency	Pathophysiological Basis
Sudden-onset unilateral pleuritic chest pain	Very common (~90%)	Air irritates the parietal pleura (which has somatic innervation from intercostal nerves). The pain is sharp, localized to the affected side, and worsened by inspiration because lung movement stretches the inflamed parietal pleura
Sudden-onset shortness of breath (SOB / dyspnoea)	Very common	Loss of ventilating lung volume → ↓ gas exchange → V/Q mismatch → hypoxaemia → stimulation of peripheral chemoreceptors and increased respiratory drive
Dry cough	Occasional	Irritation of the parietal pleura or bronchial stretch receptors by the collapsed lung
Ipsilateral shoulder tip pain	Occasional	Diaphragmatic parietal pleura irritation → referred pain via the phrenic nerve (C3–C5 dermatome → shoulder tip)
Anxiety / sense of impending doom	In large/tension PTX	Sympathetic activation due to hypoxaemia and cardiovascular compromise

Key Clinical Point

Symptom severity generally does not correlate with size of pneumothorax ^[1]. A small PSP in a fit young man may cause significant chest pain but minimal SOB. Conversely, SSP usually presents earlier and is disproportionately severe because of limited respiratory reserve ^[1] — even a small pneumothorax in a COPD patient can precipitate respiratory failure.

8.2 Signs (with Pathophysiological Basis)

Signs may be nil if small ^[1] — physical examination can be normal with small PTX (< 15% volume)

Sign	Pathophysiological Basis
Tachypnoea	Compensatory ↑ respiratory rate to maintain minute ventilation despite reduced lung volume
↓ or absent breath sounds on affected side	Air in the pleural space does not transmit sound well; collapsed lung has no air movement → no vesicular breath sounds
Hyperresonant percussion note	Air-filled pleural space resonates more than normal lung parenchyma (air is an excellent resonator)
↓ Vocal resonance / ↓ tactile vocal fremitus	Sound from the larynx is transmitted poorly through air in the pleural space (air-tissue interface reflects sound)
Reduced chest expansion on affected side	Collapsed lung does not expand; chest wall on that side moves less
Tachycardia	Sympathetic response to pain, hypoxaemia, and reduced cardiac output

Diagnostic triad for large PTX ^[1]: ↓/absent breath sounds + hyperresonant percussion + tachypnoea

Sign	Pathophysiological Basis
Marked tachycardia	Compensatory response to ↓ cardiac output from obstructive shock
Hypotension	↓ Venous return due to IVC compression by positive intrapleural pressure → ↓ preload → ↓ cardiac output
Distended neck veins (↑ JVP)	Back-pressure from IVC compression → blood cannot drain from the SVC → jugular venous distension (d/dx cardiac tamponade — both cause obstructive shock with ↑ JVP) ^[1]
Tracheal deviation away from affected side	Mediastinal shift pushed by positive pressure on the affected side
Sweating (diaphoresis)	Sympathetic activation from shock
Cyanosis	Severe hypoxaemia from bilateral ventilatory compromise
Absent breath sounds on affected side	Fully collapsed lung
Hyperresonance on affected side	Maximal air accumulation
Obstructive shock → cardiac arrest (PEA)	End-stage: complete circulatory collapse due to absent venous return

Tension PTX vs Cardiac Tamponade

Both cause obstructive shock with ↑ JVP and hypotension. The key differentiating features:

Tension PTX: Hyperresonant percussion, absent breath sounds, tracheal deviation AWAY from affected side
Cardiac tamponade: Muffled heart sounds, Beck's triad (hypotension, ↑ JVP, muffled heart sounds), no percussion/breath sound changes, pulsus paradoxus

Both may occur simultaneously in chest trauma — always check for both! ^[1]^[4]

Sign	Context	Pathophysiological Basis
Subcutaneous emphysema (surgical emphysema)	Trauma, tension PTX, Boerhaave syndrome ^[10]	Air tracks from pleural space through the parietal pleura breach into subcutaneous tissue; palpable crepitus ("rice crispy" feel)
Blunted costophrenic angle	Haemopneumothorax	Bleeding from torn pleural vessels — blood layers dependently while air rises ^[2]
Hamman's sign	Pneumomediastinum ± PTX	Mediastinal air produces a clicking/crunching sound synchronous with the heartbeat, heard on auscultation ^[10]
Sucking wound	Open pneumothorax (penetrating trauma)	Open chest wall defect allows air to enter pleural space during inspiration — audible "sucking" sound

8.3 CXR Features [1][2][11]

Rim of hyperlucency without lung markings — this is the hallmark: you see the visceral pleural line as a thin white line with no lung markings peripheral to it and normal lung markings medial to it ^[2]^[11]
The visceral pleural line runs parallel to the chest wall
If uncertain: lateral decubitus film (suspected side UP) — air rises to the non-dependent side, making it more visible ^[2]^[11]
↑ on expiratory films — lung volume decreases, making the pneumothorax relatively more conspicuous ^[11]

In trauma, patients are often supine. Air rises anteriorly in the supine position, making a conventional visceral pleural line invisible on AP film.

Deep sulcus sign: deep tongue-like costophrenic sulcus — air collects at the most anterior-inferior part of the pleural space ^[11]
Double diaphragm sign: visualization of anterior costophrenic sulcus creating a second "diaphragm" line ^[11]
Increased sharpness of adjacent mediastinal margin, diaphragm, and cardiac borders — air provides a high-contrast interface ^[11]
Depression of ipsilateral hemidiaphragm — pressure effect of trapped air ^[11]
Relative lucency of the involved hemithorax compared to the other side ^[11]

Supine CXR — Don't Miss It!

Pneumothorax is easily missed on supine CXR as usually only supine CXR is done in trauma ^[11]. Always look for the deep sulcus sign — this is the most reliable sign on supine films. If in doubt, CT chest is the gold standard for detecting occult pneumothorax.

Small: < 2 cm interpleural distance at the hilum
Large: ≥ 2 cm interpleural distance at the hilum (≈ ↓ 50% lung volume) ^[2]
% pneumothorax = (1 − [average lung diameter³ / average hemithorax diameter³]) × 100% ^[2]
1 cm on PA CXR ≈ 27% hemithorax volume ^[2]

Finding	Significance
Blunted CP angle	Haemopneumothorax — bleeding from torn pleural vessels ^[2]
Mediastinal shift to contralateral side	Tension pneumothorax or large pneumothorax
Air-fluid level	Hydropneumothorax (air + fluid in pleural space) ^[9]
Rib fractures	Traumatic pneumothorax
Bilateral pneumothorax	Requires urgent bilateral chest drains
Subcutaneous emphysema	Air in chest wall soft tissues — may indicate significant pleural/mediastinal air leak

9. Special Populations and Scenarios

Oesophageal atresia, congenital diaphragmatic hernia (CDH), and other neonatal thoracic surgical conditions predispose to perioperative pneumothorax ^[8]
Positive pressure ventilation in neonates (especially premature infants with surfactant deficiency) increases barotrauma risk ^[8]
Neonatal lungs are more susceptible to volutrauma and barotrauma due to immature alveolar structure

Pneumothorax is the most common chest trauma finding ^[10]
Multiple trauma patients ("A bus hit a train") ^[4] and "Hit by a van, in shock with internal bleeding" ^[7] — pneumothorax must be actively excluded
In the ATLS primary survey, tension PTX is identified and treated in the B (Breathing) step
FAST scan can detect pneumothorax (absence of lung sliding on ultrasound) in addition to free abdominal fluid ^[7]^[10]^[11]
Chest trauma classification ^[10]:
1. Pneumothorax
2. Aortic injury/dissection
3. Flail chest
4. Cardiac tamponade
5. Spinal fracture

Recurrent pneumothorax in menstruating women, typically right-sided (90%)
Occurs within 24–72 hours of onset of menses
Mechanism: endometrial implants on the diaphragm or visceral pleura → tissue breakdown during menstruation → air entry; or diaphragmatic fenestrations allow peritoneal air to enter pleural space
Treatment: hormonal suppression (GnRH analogues, OCPs) + surgical repair of diaphragmatic defects + pleurodesis

Increased risk of recurrence during pregnancy (Valsalva during labor)
Indication for pleurodesis if PTX occurs during pregnancy ^[1]
Management: chest drain if symptomatic; elective pleurodesis before term if recurrent

High Yield Summary

Definition: Air in the pleural space → loss of negative intrapleural pressure → lung collapse.

Epidemiology: PSP: young, tall, thin males (M:F = 3–6:1). SSP: older patients with COPD (50–70%), TB, CA lung.

Key Risk Factors: Smoking (dose-dependent, up to 20× risk), subpleural blebs, COPD, tall stature, previous PTX.

Types by mechanism: Closed (negative pressure, self-resolving), Open (atmospheric pressure, continuous leak), Tension (positive pressure, one-way valve → obstructive shock).

Tension PTX pathophysiology: One-way valve → progressive air accumulation → positive intrapleural pressure → IVC compression → ↓ venous return → obstructive shock + V/Q mismatch. CLINICAL DIAGNOSIS — do NOT wait for CXR.

Key symptoms: Sudden-onset unilateral pleuritic chest pain + dyspnoea. Severity does not correlate with size (SSP more severe due to ↓ reserve).

Key signs: Small = nil. Large = ↓ breath sounds + hyperresonance + tachypnoea. Tension = above + hypotension + ↑ JVP + tracheal deviation + shock.

CXR: Erect PA: visceral pleural line with absence of lung markings beyond it. Supine: deep sulcus sign. Size: < 2 cm = small; ≥ 2 cm = large.

O₂ therapy works by nitrogen washout — reducing blood PN₂ → steeper gradient for N₂ absorption from pleural space.

Recurrence: 10–30% at 1–5 years (PSP), 50% at 3 years (SSP).

Active Recall - Pneumothorax: Definition to Clinical Features

^[1] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155) ^[2] Senior notes: Maksim Medicine Notes.pdf (Section 12.6 Pleural diseases - Pneumothorax, p291) ^[3] Senior notes: Ryan Ho Respiratory.pdf (Section 3.2.2 COPD, p107) ^[4] Lecture slides: GC 175. A bus hit a train Multiple trauma; Disaster management.pdf ^[5] Senior notes: Ryan Ho Rheumatology.pdf (Section 5.4.3, p167 — Birt-Hogg-Dubé syndrome) ^[6] Lecture slides: GC 182. Chopped and stabbed wound in gang fight Nerves and vascular injury; Classification of injuries.pdf ^[7] Lecture slides: GC 188. Hit by a van, in shock with internal bleeding Abdominal injury.pdf ^[8] Lecture slides: GC 204. The newborn baby cannot breathe Oesophageal atresia, diaphragmatic hernia, and other surgery of lung.pdf ^[9] Senior notes: Ryan Ho Fluids and Nutrition.pdf (Section on TPN complications, p11) ^[10] Senior notes: Maksim Surgery Notes.pdf (Section 2.1 Trauma, p42) ^[11] Senior notes: Ryan Ho Radiology.pdf (Section 1.1 Chest Trauma, p2)

Differential Diagnosis of Pneumothorax

The real clinical challenge is rarely "Is this a pneumothorax?" once you see the CXR. The challenge is at the bedside, before imaging, when a patient walks in (or is wheeled in) with sudden-onset chest pain ± dyspnoea. You need a structured differential that covers the dangerous diagnoses first and works down to the benign ones. Let's build this from first principles.

Pneumothorax presents with two cardinal symptoms — sudden-onset pleuritic chest pain and dyspnoea. Neither is specific. The same presentation can be caused by conditions ranging from immediately lethal (tension PTX, massive PE, aortic dissection) to entirely benign (musculoskeletal pain, panic attack). Your job is to risk-stratify before the CXR comes back.

The DDx framework naturally divides into two clinical scenarios:

Acute chest pain — where pneumothorax sits alongside other thoracic emergencies
Acute dyspnoea — where pneumothorax competes with pulmonary, cardiac, and metabolic causes

2. Differential Diagnosis of Acute Chest Pain (Where Pneumothorax Sits)

This is the classic exam table. Pneumothorax lives among the "sudden onset, maximal at onset" group ^[12]^[13]^[14].

Diagnosis	Pain Character	Key Distinguishing Features	Why It Mimics PTX
Acute coronary syndrome (ACS)	Dull, crushing, central, radiating to jaw/arm	ECG changes (ST elevation/depression), ↑troponin, risk factors (HTN, DM, smoking, hyperlipidaemia)	Both cause acute chest pain + SOB; but ACS pain is typically dull and constricting vs PTX is sharp and pleuritic ^[12]^[13]
Aortic dissection	Tearing pain radiating to back, maximal at onset	BP differential between arms, widened mediastinum on CXR, aortic regurgitation murmur	Sudden onset and severity mimic PTX; but dissection pain is tearing and radiates to the back ^[12]
Acute pulmonary embolism (PE)	Sharp, pleuritic, ± haemoptysis	Risk factors for DVT (immobilization, surgery, OCP), sinus tachycardia, S1Q3T3 on ECG, ↑D-dimer, CTPA positive	The closest mimic — both cause sudden pleuritic pain + SOB + tachycardia. PE has haemoptysis and DVT signs; PTX has absent breath sounds and hyperresonance ^[12]^[15]
Tension or massive pneumothorax	Sharp, pleuritic, unilateral	Absent breath sounds, hyperresonance, tracheal deviation, obstructive shock	This is the severe end of the pneumothorax spectrum itself
Pneumonia	Pleuritic (due to pleural inflammation)	Fever, productive cough, crackles/bronchial breathing, consolidation on CXR, ↑WCC/CRP	Pleuritic pain overlaps; but pneumonia has dullness to percussion (opposite of PTX hyperresonance) and fever ^[16]
Myopericarditis ± cardiac tamponade	Sharp, pleuritic, positional (better sitting forward)	Pericardial rub, diffuse ST elevation on ECG, pericardial effusion on echo; tamponade: Beck's triad	Pleuritic pain mimics PTX; but pericarditis is positional (worse lying flat) and has widespread ECG changes
Acute decompensated heart failure	Chest tightness, dyspnoea	Bilateral crackles, ↑JVP, peripheral oedema, gallop rhythm, cardiomegaly on CXR	SOB overlaps; but HF has bilateral crackles and cardiomegaly, not unilateral absent breath sounds

Diagnosis	Pain Character	Key Distinguishing Features	Why It Mimics PTX
Small pneumothorax	Mild pleuritic pain	Self-limiting, minimal haemodynamic compromise	Small PTX itself — the benign end of the spectrum
GERD	Retrosternal burning	Worse after meals/lying down, relieved by antacids, no respiratory signs	Retrosternal chest pain; but no respiratory signs and burning quality ^[12]
Musculoskeletal pain	Sharp, localized, reproducible with palpation	History of exertion or trauma, tender on palpation (e.g., costochondritis — Tietze syndrome)	Sharp chest pain; but pain after exertion (not during), reproducible with movement/palpation ^[12]
Panic attack	Variable, often described as "chest tightness"	Hyperventilation, perioral/digital paraesthesiae, no objective respiratory findings, resolves spontaneously	SOB + chest pain in a young patient; but examination and investigations are completely normal
Episode of stable angina	Dull, exertional, relieved by rest/nitrates	Predictable relationship with exertion, lasts < 5–10 min	Chest pain with SOB; but predictable with exertion and relieved by rest

The Big Five of Acute Chest Pain

In any exam question about acute chest pain, always consider the "big five" life-threatening diagnoses ^[13]^[14]:

ACS — crushing central pain, ECG + troponin
Aortic dissection — tearing back pain, BP differential
Pulmonary embolism — pleuritic pain + DVT risk factors
Tension pneumothorax — absent breath sounds + shock
Cardiac tamponade — Beck's triad (muffled hearts sounds, ↑ JVP, hypotension)

Rule these out first, then consider benign causes.

Pneumothorax also presents primarily with dyspnoea, especially in SSP where pain may be less prominent ^[2]^[17].

Category	Differential	Key Distinguishing Features
Respiratory — Acute	Pneumothorax	Absent breath sounds + hyperresonance
	PE	DVT signs, ↑D-dimer, CTPA
	Acute severe asthma	Diffuse bilateral wheeze, history of asthma, response to bronchodilators
	AECOPD	Known COPD, productive cough, bilateral wheeze ± crackles
	Pneumonia	Fever, productive cough, consolidation signs
Respiratory — Subacute	Pleural effusion	Stony dull percussion, ↓ breath sounds (cf. hyperresonant in PTX)
	TB	Chronic cough, night sweats, weight loss
Cardiac	Acute pulmonary oedema (APO)	Bilateral fine crackles, pink frothy sputum, ↑ JVP, gallop rhythm ^[16]
	ACS	Central crushing pain, ECG changes
	Arrhythmia	Palpitations, irregular pulse, ECG diagnostic
Metabolic	Anaemia	Pallor, ↑ HR, flow murmur
	Metabolic acidosis (e.g., DKA)	Kussmaul breathing, ↑ anion gap, history of DM
	Hyperthyroidism	Tremor, weight loss, goitre, AF
Neuromuscular	Myasthenia gravis	Fatigable weakness, diplopia, ptosis
	Guillain-Barré syndrome	Ascending weakness, areflexia
Psychological	Panic attack / hyperventilation	Perioral paraesthesiae, sighing, normal examination ^[17]

4. Differential Diagnosis Specific to Physical Signs

When you stand at the bedside, the physical examination pattern helps narrow the DDx. Here's the critical comparison table:

Feature	Pneumothorax	Pleural Effusion	Consolidation
Percussion	Hyperresonant	Stony dull	Dull
Breath sounds	↓ / Absent	↓ / Absent	Bronchial breathing
Vocal resonance	↓	↓	↑ (whispering pectoriloquy)
Tactile vocal fremitus	↓	↓	↑
Tracheal position	Pushed away (if tension/large)	Pushed away (if massive)	Central or pulled toward (if collapse)
Mediastinal shift	Away from lesion	Away from lesion (if large)	Toward lesion (if associated atelectasis)
Why?	Air reflects sound and doesn't conduct vibrations; air resonates on percussion	Fluid dampens sound and doesn't conduct vibrations; fluid is dense → dull	Solid consolidated lung transmits sound well (like a solid conductor); dense tissue → dull percussion

The Percussion Test is Your Best Friend

When you find unilateral ↓ breath sounds, percussion tells you everything:

Hyperresonant → Air (pneumothorax or hyperinflation)
Stony dull → Fluid (pleural effusion)
Dull → Solid (consolidation, mass)

This single test often clinches the bedside diagnosis before any imaging.

Both cause obstructive shock with ↑ JVP — a favourite exam comparison ^[1]^[16].

Feature	Tension Pneumothorax	Cardiac Tamponade
Percussion	Hyperresonant on affected side	Normal
Breath sounds	Absent on affected side	Normal
Trachea	Deviated AWAY from affected side	Central
Heart sounds	Normal	Muffled
Pulsus paradoxus	May be present	Classically present
Neck veins	Distended	Distended (Kussmaul sign)
CXR	Absent lung markings, mediastinal shift	Globular heart ("flask-shaped"), clear lung fields
Bedside USG	Absent lung sliding	Pericardial effusion, RV diastolic collapse
Treatment	Needle decompression → chest drain	Pericardiocentesis

5. Differential Diagnosis by Context

After CVC insertion, pleural procedures, or mechanical ventilation ^[1]^[2]^[9], any acute deterioration in respiratory status should prompt consideration of iatrogenic PTX:

Post-procedure Scenario	Differential	How to Distinguish from PTX
After CVC insertion (subclavian/IJV)	Pneumothorax, haemothorax, hydrothorax, air embolism	CXR: PTX shows visceral pleural line; haemothorax shows blunting; hydrothorax shows fluid level ^[9]
After thoracocentesis	PTX (lung punctured), re-expansion pulmonary oedema (RPO)	RPO: cough, desaturation, unilateral alveolar shadowing on CXR; improves on clamping drain ^[1]
During mechanical ventilation	Barotrauma → tension PTX	Sudden ↑ airway pressure + ↓ SpO₂ + ↓ BP + unilateral absent breath sounds → clinical diagnosis ^[1]^[2]
After transthoracic lung biopsy	PTX (most common complication, up to 20%)	Post-procedure CXR; small PTX may be observed, large PTX needs aspiration/drain

In the trauma setting ("hit by a van," "a bus hit a train," "chopped and stabbed wound in gang fight") ^[4]^[6]^[7], pneumothorax must be differentiated from:

Condition	Key Features	How It Differs from PTX
Haemothorax	Dullness to percussion (blood is fluid), ↓ breath sounds	Dull (not hyperresonant); drain produces blood, not air
Flail chest	Paradoxical chest wall movement, multiple rib fractures (≥ 2 fractures in ≥ 2 consecutive ribs)	Visible/palpable paradoxical segment; PTX may coexist
Cardiac tamponade	Muffled heart sounds, ↑ JVP, hypotension (Beck's triad)	Normal percussion and breath sounds; pericardial effusion on FAST
Aortic injury/dissection	Widened mediastinum on CXR, BP differential, mechanism (deceleration)	CXR shows widened mediastinum, not absent lung markings
Diaphragmatic rupture	Bowel sounds in chest, NG tube visible in thorax on CXR	CXR may show gas-filled bowel in hemithorax; can mimic a loculated PTX
Pulmonary contusion	Diffuse haziness on CXR, hypoxia, no visceral pleural line	CXR shows parenchymal opacification, not hyperlucency; often coexists with PTX ^[11]
Oesophageal perforation (Boerhaave syndrome)	Mackler's triad: vomiting, excruciating chest pain, surgical emphysema; left pneumothorax, left pleural effusion ^[10]	History of violent vomiting; pneumomediastinum on CXR; CT with contrast swallow confirms

In neonates ("the newborn baby cannot breathe") ^[8], acute respiratory distress with signs mimicking PTX:

Condition	Distinguishing Features
Congenital diaphragmatic hernia (CDH)	Scaphoid abdomen, bowel sounds in chest, CXR shows bowel loops in thorax
Oesophageal atresia (OA)	Unable to pass NG tube, excessive drooling, coiled NG tube on CXR
Neonatal pneumothorax (from barotrauma)	During/after positive pressure ventilation; transillumination positive
Respiratory distress syndrome (RDS)	Premature infant, ground-glass appearance on CXR, responds to surfactant
Meconium aspiration	Term/post-term, meconium-stained liquor, hyperinflation + patchy opacities on CXR
Congenital cystic adenomatoid malformation (CPAM)	Multicystic lung mass on CXR/antenatal USS — can mimic loculated PTX

Clue	Favours Pneumothorax	Favours Alternative
Onset	Sudden, maximal at onset	Gradual buildup → ACS; post-exertional → MSK
Pain quality	Sharp, pleuritic	Dull/crushing → ACS; tearing → dissection; burning → GERD
Percussion	Hyperresonant	Dull → effusion/consolidation; normal → PE/ACS
Breath sounds	Absent/↓ unilaterally	Crackles → APO/pneumonia; wheeze → asthma/COPD; bronchial → consolidation
Tracheal position	Pushed away (tension/large)	Pulled toward → collapse/fibrosis
CXR	Visceral pleural line, no lung markings	White-out → effusion/collapse; consolidation → pneumonia; normal → PE/ACS
Response to O₂	Improves (if not tension)	No improvement → shunt (consolidation); worsens → consider Haldane effect in CO poisoning
Trauma history	Strongly favours PTX (especially with rib fractures)	Absent → consider spontaneous causes
Fever	Absent (unless coexisting infection)	Present → pneumonia, empyema
Smoking/COPD history	Strongly favours SSP if present	Absent in young → PSP vs other causes

Common Mistakes in DDx of Pneumothorax

Confusing PTX with pleural effusion: Both have ↓ breath sounds, but percussion is the differentiator (hyperresonant vs stony dull). Students often forget to mention percussion in OSCE.
Missing tension PTX on ventilator: A ventilated patient who suddenly desaturates with ↑ airway pressures — always think tension PTX. The one-way valve is created because PPV forces air into the pleural space but the collapsed lung cannot seal the leak ^[1].
Forgetting PE as the closest mimic: PE and PTX both cause sudden pleuritic pain + SOB + tachycardia. The key is examination (PTX has unilateral signs; PE often has a normal chest exam) and CXR (PTX shows pleural line; PE shows normal or subtle signs like Hampton's hump/Westermark sign).
Not considering Boerhaave syndrome: A history of violent vomiting followed by chest pain + subcutaneous emphysema + left-sided pleural effusion/pneumothorax = think oesophageal perforation ^[10]. The oesophagus has no serosa, making it susceptible to full-thickness rupture.
Forgetting CDH in neonates: A newborn with respiratory distress and what looks like a "pneumothorax" on CXR may actually have bowel loops in the chest from congenital diaphragmatic hernia ^[8]. Look for the scaphoid abdomen.

High Yield Summary

DDx Framework for Pneumothorax:

By presenting symptom (acute chest pain): ACS, aortic dissection, PE, tension PTX, cardiac tamponade, pneumonia, pericarditis (life-threatening); stable angina, GERD, MSK pain, small PTX, panic attack (benign).

Key bedside differentiator: PERCUSSION — hyperresonant = air (PTX); stony dull = fluid (effusion); dull = solid (consolidation).

Closest mimic: PE — both cause sudden pleuritic pain + SOB + tachycardia. Differentiate by chest exam (unilateral signs in PTX, often normal in PE) and CXR.

Obstructive shock DDx: Tension PTX vs cardiac tamponade — differentiate by percussion (hyperresonant vs normal), breath sounds (absent vs normal), trachea (deviated vs central), heart sounds (normal vs muffled).

Trauma context: Must differentiate from haemothorax (dull percussion), flail chest (paradoxical movement), cardiac tamponade, aortic injury, diaphragmatic rupture, pulmonary contusion.

Post-procedure: After CVC/thoracic procedure, acute respiratory deterioration = PTX until proven otherwise.

Neonatal: CDH (bowel in chest) can mimic PTX on CXR.

Don't forget: Boerhaave syndrome (vomiting + chest pain + surgical emphysema + left PTX).

Active Recall - Differential Diagnosis of Pneumothorax

References

^[1] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155) ^[2] Senior notes: Maksim Medicine Notes.pdf (Section 12.6 Pleural diseases - Pneumothorax, p291) ^[4] Lecture slides: GC 175. A bus hit a train Multiple trauma; Disaster management.pdf ^[6] Lecture slides: GC 182. Chopped and stabbed wound in gang fight Nerves and vascular injury; Classification of injuries.pdf ^[7] Lecture slides: GC 188. Hit by a van, in shock with internal bleeding Abdominal injury.pdf ^[8] Lecture slides: GC 204. The newborn baby cannot breathe Oesophageal atresia, diaphragmatic hernia, and other surgery of lung.pdf ^[9] Senior notes: Ryan Ho Fluids and Nutrition.pdf (Section on TPN complications, p11) ^[10] Senior notes: Maksim Surgery Notes.pdf (Section 2.1 Trauma, p42; Esophageal perforation, p59) ^[11] Senior notes: Ryan Ho Radiology.pdf (Section 1.1 Chest Trauma, p2) ^[12] Senior notes: Ryan Ho Cardiology.pdf (Section 2.1 Chest Pain, p54–57) ^[13] Senior notes: Ryan Ho Cardiology.pdf (Section 2, Approach to Acute Chest Pain, p58) ^[14] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.1.1 Chest Pain, p199–203) ^[15] Senior notes: Ryan Ho Haemtology.pdf (Section on VTE, p131) ^[16] Senior notes: Ryan Ho Critical Care.pdf (Section on Breathing emergencies, p14) ^[17] Senior notes: Maksim Medicine Notes.pdf (Section 12.1 Clinical approach - Dyspnoea, p280)

Diagnostic Criteria, Algorithm, and Investigations for Pneumothorax

1. Diagnostic Criteria — What Confirms a Pneumothorax?

Unlike many medical conditions (e.g., rheumatoid arthritis, SLE) that have formal consensus diagnostic criteria with scoring systems, pneumothorax does not have "diagnostic criteria" in the traditional sense. Instead, diagnosis is based on a combination of clinical assessment and imaging confirmation — except in one critical scenario where imaging must NOT be awaited.

Tension pneumothorax is a clinical diagnosis ^[1]^[2]. You diagnose and treat it at the bedside:

Required Element	Finding
Clinical context	Trauma, mechanical ventilation, post-procedure, or spontaneous
Severe respiratory distress	Tachypnoea, cyanosis
Obstructive shock signs	Hypotension, elevated JVP, marked tachycardia, sweating ^[2]
Unilateral chest signs	Absent breath sounds + hyperresonance on affected side
Mediastinal shift	Contralateral tracheal deviation ^[1] (may be absent if mediastinum is splinted by malignancy/scarring ^[1])

Tension PTX — DO NOT Wait for CXR

Tension pneumothorax should NOT be diagnosed based on CXR ^[1]. If you clinically suspect it — absent breath sounds, hyperresonance, shock, tracheal deviation — proceed immediately to needle decompression. Waiting for imaging wastes time and the patient may arrest from obstructive shock. This is the only pneumothorax that is diagnosed purely clinically.

For all other pneumothoraces, the diagnosis rests on imaging that demonstrates air in the pleural space:

Modality	Diagnostic Finding	When to Use
Erect PA CXR	Visible visceral pleural edge + radiolucency with no lung markings peripheral to lung edge ^[2]^[11]^[18]	First-line — standard diagnostic investigation for suspected PTX
Expiratory film	Accentuates the degree of lung collapse — makes the visceral pleural line more conspicuous ^[18]^[19]	When inspiratory CXR is equivocal
Lateral decubitus film	Suspected side UP — air rises to the non-dependent hemithorax ^[2]	When erect CXR is equivocal; distinguish from effusion (effusion: suspected side DOWN)
Supine AP CXR	Deep sulcus sign, double diaphragm sign, relative hemithorax lucency ^[11]	Trauma/immobilised patients — more difficult to interpret
CT thorax	Gold standard for detection; identifies small/occult PTX, blebs, underlying lung disease	When CXR is equivocal, post-procedure evaluation, or to plan surgical intervention
Bedside lung ultrasound	Absent lung sliding, absent comet-tail artefacts, "lung point" sign	Rapid bedside assessment, especially in trauma (E-FAST) and ICU

Key principle: A pneumothorax is confirmed when imaging demonstrates the visceral pleural line separated from the chest wall by a space devoid of lung markings. The visceral pleura appears as a thin white line running parallel to the chest wall. Peripheral to this line = air only (black, no vascular markings). Medial to this line = normal lung parenchyma.

Once confirmed, the pneumothorax must be sized, as this determines management:

Size	BTS Definition	Volume Estimation
Small	< 2 cm interpleural distance at the hilum on erect PA CXR ^[2]	Approximately < 50% hemithorax
Large	≥ 2 cm interpleural distance at the hilum on erect PA CXR ^[2]	Approximately ≥ 50% hemithorax

Quantification formula ^[2]:

% pneumothorax = (1 − [average lung diameter³ / average hemithorax diameter³]) × 100%

Approximation: 1 cm on PA CXR ≈ 27% hemithorax volume ^[2]

Why is this formula cubic? Because volume is a three-dimensional quantity — when the lung shrinks by a certain linear distance from the chest wall, the volume change scales with the cube of that distance (V = 4/3 πr³ for a sphere-like structure).

BTS vs ACCP Size Thresholds

BTS (used in HK): measures interpleural distance at the hilum level — small < 2 cm, large ≥ 2 cm. ACCP (American): measures interpleural distance at the apex — small < 3 cm, large ≥ 3 cm. These are different measurement points and should not be confused. HKU/HK practice generally follows BTS guidelines.

The management algorithm is inherently linked to the diagnostic pathway because the decision to investigate vs. treat immediately depends on haemodynamic stability and clinical severity. Below is the comprehensive diagnostic-management decision tree based on BTS 2023 guidelines (which HK follows):

Key Decision Points in the Algorithm

Haemodynamic stability is assessed FIRST — this determines whether you go straight to needle decompression (tension PTX) or proceed with orderly imaging.
PSP vs SSP distinction matters because SSP patients have less reserve:
- PSP: chest drain if ≥ 2 cm or symptomatic ^[2]
- SSP: chest drain if ≥ 1 cm or symptomatic ^[2]
- This lower threshold for SSP reflects the fact that even a small PTX can cause respiratory failure in patients with pre-existing lung disease.
Needle aspiration is attempted FIRST in PSP (large or symptomatic) because many will resolve without requiring a chest drain. In SSP, aspiration can be tried for intermediate sizes (1–2 cm) but the threshold for proceeding to a drain is lower.
Bilateral PTX and haemodynamically unstable patients always get chest drains ^[2].

3. Investigation Modalities — Detailed Guide

3.1 Chest X-Ray (CXR) — First-Line Investigation

The erect PA CXR is the standard first-line diagnostic investigation for pneumothorax ^[2]^[11]^[18]^[19].

Why erect PA? In an erect patient, air rises to the apex of the hemithorax, where it is most easily seen as a visceral pleural line. The PA projection provides better spatial accuracy than AP because the X-ray source is further from the patient (standard 6-foot distance), reducing magnification artifact.

Finding	Description	Pathophysiological Basis
Visible visceral pleural edge	Thin white line running parallel to chest wall ^[11]^[19]	The visceral pleura itself — air on both sides (pleural space air laterally, lung air medially) makes it visible as a line
Radiolucency with no lung markings peripheral to lung edge ^[2]^[11]	Black area beyond the pleural line with no vascular markings	Air in pleural space contains no vessels — therefore no lung markings
± lung collapse ^[11]	Lung retracted toward hilum, appearing as a density medially	Elastic recoil pulls the unsupported lung inward
± mediastinal shift ^[11]	Heart and trachea shifted to contralateral side	Large or tension PTX: positive pressure pushes mediastinum away
Blunted CP angle	Loss of normal sharp costophrenic angle ^[2]	Bleeding from torn pleural vessels → haemopneumothorax ^[2]; blood layers dependently
Subcutaneous emphysema	Air in soft tissues of chest wall (tracking along tissue planes)	Air from pleural space dissects through parietal pleura into subcutaneous tissue

Feature	Erect PA CXR	Supine AP CXR
Air location	Rises to apex	Rises anteriorly (not visible at apex)
Classic finding	Visceral pleural line at apex/laterally	Deep sulcus sign (most reliable) ^[11]
Sensitivity	~80% for moderate-large PTX	Much lower — easily missed ^[11]
When used	Standard — any ambulatory patient	Trauma — patients on spinal board ^[11]

Supine CXR findings ^[11]:

Deep sulcus sign: deep tongue-like costophrenic sulcus — air collects at the most anterior and inferior part of the pleural space
Double diaphragm sign: visualization of anterior costophrenic sulcus — creates a second "diaphragm" line
↑ sharpness of adjacent mediastinal margin, diaphragm and cardiac borders — air provides high-contrast interface
Depression of ipsilateral hemidiaphragm — pressure from trapped air
Relative lucency of the involved hemithorax — the overall hemithorax appears blacker

Technique	How It Helps	Physics
Expiratory film	Accentuates degree of lung collapse ^[18]^[19]	During expiration, lung volume ↓ → the relative size of the pneumothorax space ↑ → more conspicuous pleural line
Lateral decubitus film (suspected side UP) ^[2]	Air rises to the non-dependent hemithorax, becoming more visible	Gravity moves air to the uppermost point; opposite to effusion technique (suspected side DOWN)

Before interpreting any CXR, systematically check:

Name, date, L/R label (rule out dextrocardia) ^[19]
Adequacy of inspiration: count 10 posterior ribs + 6 anterior ribs ^[19]
Rotation: medial ends of clavicle equidistant from spinous process ^[19]
Penetration: retrocardiac window and T-spine outline just visible ^[19]

Then look for:

Lung border: retracted in pneumothorax ^[19]
Costophrenic angles: blunted in effusion/haemothorax
Cardiac silhouette: enlarged in cardiomegaly
Bony lesions: rib fractures (traumatic PTX)
Loss of silhouette sign: pathology → ↑ density of lung fields → ↓ contrast with overlying structure ^[19]

Exam Pitfall: Skin Fold vs Visceral Pleural Line

A common mistake is confusing a skin fold on CXR with a visceral pleural line. The differences:

Visceral pleural line: Thin, sharp, runs parallel to chest wall, no lung markings BEYOND the line
Skin fold: Thicker, may not run parallel, lung markings are visible BEYOND the fold (because it's just a superficial artefact)

If in doubt, order a CT thorax — this is the gold standard and will definitively show even tiny amounts of pleural air.

3.2 CT Thorax — Gold Standard

CT thorax is the most sensitive and specific imaging modality for pneumothorax. It can detect even tiny amounts of pleural air invisible on CXR.

Indication	Rationale
Equivocal CXR with high clinical suspicion	CT resolves ambiguity (skin fold vs pleural line, bullae vs PTX)
Occult pneumothorax in trauma	Up to 50% of traumatic PTX are missed on supine CXR but detected on CT ^[11]
Planning for surgical intervention	Identifies blebs/bullae location, extent of lung disease, contralateral lung status
Persistent air leak (≥ 5 days)	CT thorax to localise lesion before considering EBV or surgical pleurodesis ^[2]
SSP — identifying underlying lung disease	COPD bullae, TB cavities, lung cysts (LAM, LCH), malignancy
Recurrent PTX evaluation	Determine if blebs/bullae are present bilaterally, plan definitive surgery
Suspected associated pathology	Haemothorax, mediastinal injury, oesophageal perforation

CT is the gold standard for head and body trauma ^[11]:

IV contrast is needed unless contraindicated ^[11]
Arterial phase: for bleeding points and pseudoaneurysm
Portovenous phase (most important): visceral injury
Delayed phase: urinary extravasation
Lung and bone window: lung window is essential for detecting pneumothorax — the different window/level settings optimise contrast for air (lung window) vs soft tissue vs bone

Finding	Significance
Air in pleural space	Confirms PTX; quantifies size more accurately than CXR
Subpleural blebs/bullae (usually apical)	Identifies the likely source of air leak; important for surgical planning
Underlying lung disease	COPD (emphysema, bullae), TB (cavities, fibrosis), cystic lung disease (LAM, LCH), malignancy
Pneumomediastinum	Air tracking along mediastinal structures; may indicate proximal airway injury or Macklin effect
Associated injuries (trauma)	Rib fractures, haemothorax, pulmonary contusion, aortic injury
Loculated collections	Suggest previous adhesions or empyema; important for drain positioning

3.3 Bedside Lung Ultrasound (Point-of-Care USG)

Lung ultrasound has become increasingly important, especially in trauma (as part of E-FAST — Extended FAST) and ICU settings ^[11]^[16].

Finding	Normal Lung	Pneumothorax	Explanation
Lung sliding	Present — shimmering movement at pleural line with respiration	Absent — no movement at pleural line	Normally, the visceral pleura slides against the parietal pleura during breathing. Air between the layers prevents this sliding.
Comet-tail artefacts (B-lines)	Present — vertical hyperechoic lines from pleural line	Absent	B-lines arise from the acoustic interface of aerated lung against the pleura. Air in the pleural space eliminates this interface.
"Lung point" sign	Not applicable	Present — transition point where lung sliding appears and disappears	The "lung point" is where the edge of the collapsed lung intermittently touches the chest wall. It is pathognomonic for pneumothorax and can estimate the size of PTX.
"Seashore sign" (M-mode)	Normal pattern — granular pattern below pleural line	Replaced by "stratosphere sign" (barcode sign) — horizontal parallel lines	In M-mode, normal lung movement creates a granular pattern; absence of movement (air in pleural space) creates uniform horizontal lines.

The thoracic views of the FAST scan specifically look for pneumothorax and haemothorax ^[11]:

E-FAST View	What to Look For
Pericardial window	Pericardial effusion
R flank	Morrison's pouch, subphrenic, pleural, right paracolic gutter
L flank	Splenorenal space, subphrenic, pleural, left paracolic gutter
Pelvis	Pouch of Douglas / rectovesical space
± Thoracic (left and right)	Pneumothorax and haemothorax ^[11]

Ultrasound Sensitivity for PTX

Lung ultrasound has a sensitivity of ~90–95% and specificity of ~98–100% for pneumothorax — significantly better than supine CXR (~50% sensitivity). It is faster than CXR, radiation-free, and can be done at the bedside. However, it is operator-dependent and may miss small posterior pneumothoraces. CT remains the gold standard when ultrasound is inconclusive.

ABG is not diagnostic for pneumothorax itself but is essential for assessing the physiological impact:

Finding	Interpretation	When Seen
↓ PaO₂ (hypoxaemia)	V/Q mismatch — collapsed lung is perfused but not ventilated	Any significant PTX; worse in SSP
Normal or ↓ PaCO₂	Compensatory hyperventilation driving down CO₂	Small-moderate PTX in patients with normal lung reserve
↑ PaCO₂ (hypercapnia)	Alveolar hypoventilation — insufficient remaining lung for CO₂ clearance	Large PTX, bilateral PTX, or SSP with pre-existing poor reserve (Type 2 respiratory failure)
↑ A-a gradient	Confirms intrapulmonary pathology (V/Q mismatch or shunt) as the cause of hypoxaemia, rather than pure hypoventilation	Present in PTX (V/Q mismatch); helps distinguish from neuromuscular causes of respiratory failure where A-a gradient is normal
Lactic acidosis	Poor tissue perfusion ^[16]	Tension PTX with obstructive shock
Respiratory alkalosis	Hyperventilation → ↓ PaCO₂ → ↑ pH	Common in acute PTX with pain and anxiety

Blood tests do not diagnose pneumothorax but serve to:

Exclude differentials (e.g., PE, ACS)
Assess physiological impact of the PTX
Identify underlying causes (e.g., infections in SSP)
Prepare for intervention (e.g., clotting before chest drain)

Investigation	Findings/Role	Reasoning
CBC	↑ WCC (if infective cause of SSP, e.g., TB, PCP); anaemia if associated haemothorax ^[16]	Baseline; r/o haemorrhage
CRP/ESR	↑ in infective/inflammatory SSP	Non-specific marker of inflammation
Clotting profile (PT/INR, aPTT)	Baseline before chest drain insertion; identify bleeding risk	Essential before any invasive procedure
Renal function (U&E/Cr)	Baseline; ↑ U/Cr in shock-induced AKI ^[16]	Assess end-organ perfusion
LFT	↑ ALT/AST in "shock liver" from tension PTX ^[16]	Assess end-organ perfusion
Cardiac enzymes (troponin)	R/o ACS as differential; may be mildly elevated in tension PTX (demand ischaemia) ^[16]	Distinguish from MI
D-dimer	R/o PE as differential ^[16]	Sensitive but not specific; mainly used to exclude PE
ABG/VBG + lactate	As above — assess ventilation, oxygenation, perfusion ^[16]	Guide O₂ therapy and ventilatory support

ECG is not diagnostic for pneumothorax but is performed to exclude other causes of acute chest pain (ACS, PE, pericarditis) ^[13]^[16]:

Finding	Interpretation
Sinus tachycardia	Most common ECG finding in PTX — sympathetic response to pain/hypoxia
Right axis deviation	Large right-sided PTX or tension PTX — right heart strain
Low-voltage QRS	Air in pleural space insulates the heart from chest wall electrodes
Precordial T-wave inversion (V1–V3)	Right heart strain pattern (can mimic PE or ACS)
Rightward shift of precordial transition zone	Air in left hemithorax shifts the electrical axis
ST changes	Can mimic ACS — but transient and resolve after PTX treatment
R/o ACS: ST elevation/depression	Must exclude ACS in any acute chest pain ^[13]
R/o PE: S1Q3T3, RBBB	Right heart strain pattern of PE ^[16]
R/o pericarditis: diffuse concave ST elevation + PR depression	Pericarditis pattern

ECG Pitfall in Left PTX

A large left-sided pneumothorax can cause precordial voltage changes and axis shifts that mimic anterior MI. Always correlate with the CXR! If the "ST changes" resolve after PTX drainage, they were a pneumothorax artefact, not true ischaemia.

Investigation	When	Purpose
HRCT thorax	SSP — to identify underlying disease	Detect COPD bullae, TB cavities, cystic lung disease, malignancy
Sputum AFB + TB culture	SSP in TB-endemic region (HK)	Rule out active TB as cause
HIV test	Young patient with PCP-type presentation	PCP-associated PTX
α₁-antitrypsin level	Young Caucasian with emphysema pattern	Rare cause of emphysema → bullae → PTX
Genetic testing (FLCN gene)	Basilar lung cysts + family history + skin lesions	Birt-Hogg-Dubé syndrome
Hormonal assessment	Catamenial PTX (recurrent, right-sided, menstrual)	Endometriosis evaluation

4. Approach to Specific Diagnostic Scenarios

Scenario	Investigation	Action
After CVC insertion	CXR mandatory post-procedure ^[9]	Confirm line position + r/o PTX, haemothorax, hydrothorax
After transthoracic biopsy	CXR at 1h and 4h post-procedure	PTX is the most common complication (~20%); most are small and self-limiting
During mechanical ventilation	Clinical assessment + bedside USG + portable CXR	Sudden ↑ airway pressure + ↓ SpO₂ + ↓ BP = tension PTX until proven otherwise
After thoracocentesis	Repeat CXR	R/o PTX (2–15% complication rate) ^[20]

Definition: air leak ≥ 5 days despite chest drain ^[2]

When air continues to bubble through the underwater seal:

CT thorax to localise the lesion ^[2]
Consider bronchoscopy — can identify the specific segmental/lobar bronchus responsible for the leak
Endobronchial valve (EBV) may be placed under bronchoscopic guidance — a one-way valve that intentionally collapses the affected lung lobe → remove 6 weeks after recovery (foreign body) ^[2]

Investigation	Role in PTX Diagnosis	Key Findings	Sensitivity
Erect PA CXR	First-line diagnostic	Visceral pleural line + hyperlucency	~80% for moderate-large PTX
Expiratory film	Adjunct — enhances detection	Accentuates lung collapse ^[18]^[19]	Better than inspiratory for small PTX
Lateral decubitus	Adjunct — equivocal cases	Air rises to non-dependent side ^[2]	Good for small PTX
Supine AP CXR	Trauma setting	Deep sulcus sign, double diaphragm sign ^[11]	~50% — easily missed
CT thorax	Gold standard	Detects any pleural air + underlying disease	~100%
Bedside USG	Rapid bedside assessment	Absent lung sliding, lung point ^[11]^[16]	90–95%
ABG	Physiological impact	Hypoxaemia, ↑ A-a gradient, ± lactic acidosis	N/A (supportive)
ECG	R/o differentials	Sinus tachycardia, axis shift, r/o ACS/PE ^[16]	N/A (supportive)
Blood tests	R/o differentials + pre-procedure	CBC, clotting, cardiac enzymes, D-dimer ^[16]	N/A (supportive)
HRCT	Identify underlying lung disease (SSP)	Blebs, bullae, cysts, cavities, malignancy	N/A (aetiological)

High Yield Summary

Tension PTX = clinical diagnosis — do NOT wait for CXR. Treat immediately with needle decompression.

All other PTX = diagnosed by erect PA CXR (first-line) showing visceral pleural line + hyperlucency without lung markings.

Equivocal CXR → expiratory film (accentuates collapse) or lateral decubitus (suspected side up) or CT thorax (gold standard).

Supine CXR (trauma) → look for deep sulcus sign (most reliable), double diaphragm sign, relative hemithorax lucency. Easily missed.

CT thorax = gold standard for detection + underlying cause identification. Essential for persistent air leak (≥ 5 days) to localise lesion.

Bedside USG = absent lung sliding + absent B-lines + lung point sign (pathognomonic). Sensitivity 90–95% — better than supine CXR.

Size on CXR (BTS): Small < 2 cm at hilum; Large ≥ 2 cm. 1 cm ≈ 27% hemithorax volume.

Key bloods: Not diagnostic but essential — ABG (hypoxaemia, A-a gradient), CBC, clotting (pre-procedure), cardiac enzymes (r/o ACS), D-dimer (r/o PE).

ECG: Sinus tachycardia most common; left PTX can mimic anterior MI — correlate with CXR.

Post-CVC CXR is mandatory to rule out iatrogenic PTX.

Active Recall - Pneumothorax: Diagnosis and Investigations

References

Management of Pneumothorax

Before diving into the algorithm, understand the two overarching goals of pneumothorax management:

Acute management: Remove air from the pleural space → restore lung expansion → relieve symptoms
Definitive management: Prevent recurrence → obliterate the pleural space or remove the source of air leak

The choice of acute treatment depends on three key considerations ^[1]:

Symptoms: SOB → need for active intervention ^[1]
Size: Determines rate of spontaneous resorption → large PTX with few symptoms may still need intervention ^[1]
Comorbidities: Poor lung reserve → active treatment despite small size ^[1]

The philosophy is simple: a fit young person with a small PSP can wait for spontaneous reabsorption. An elderly COPD patient with a small SSP cannot — they have no reserve and may decompensate. This is why the thresholds differ.

3. Acute Management — Removing Air from the Pleural Space

O₂ therapy ^[2]:

Mechanism: to promote absorption of air (O₂ easier to absorb than N₂) ^[2]

Let me explain this from first principles. The air trapped in the pleural space is approximately 79% nitrogen (N₂) and 21% oxygen (O₂). N₂ is poorly soluble in blood and reabsorbs slowly — at a rate of roughly 1.25% of hemithorax volume per day on room air. When you give high-concentration O₂, you "nitrogen-wash" the blood: alveolar O₂ displaces N₂ → blood PN₂ drops → a steeper diffusion gradient forms between the pleural air (high PN₂) and blood (low PN₂) → N₂ is absorbed 4–6× faster, increasing resorption to ~6% per day.

O₂ Target	PSP	SSP
SpO₂ target	≥ 96% (high-flow O₂ at 6 L/min or above)	≥ 88–92% (titrate carefully; some COPD patients retain CO₂ on high O₂)
Delivery	Nasal cannula or face mask with reservoir	Face mask; titrate to avoid CO₂ retention in chronic retainers

What NOT to Give

Avoid high-flow nasal cannula (HFNC) and NIPPV: positive pressure may worsen PTX ^[2]. These modalities deliver positive pressure, which can force more air through the pleural defect or convert a simple PTX into tension physiology. Similarly, positive pressure ventilation (PPV) in the presence of pneumothorax may lead to tension pneumothorax — ventilation is therefore difficult in pneumothorax complicating lung disease ^[1].

Indication:

Asymptomatic PSP ≤ 2 cm ^[1]
Asymptomatic SSP ≤ 1 cm ^[1]

What it involves:

High-flow O₂ (to accelerate resorption)
Observe for 4–6 hours with repeat CXR
Discharge with early CXR follow-up in 2–4 weeks ^[1]
Pain management with simple analgesics (paracetamol ± opioids if needed)

Why does this work? In a small, closed pneumothorax, the air leak has sealed itself. The remaining air will be gradually reabsorbed down the partial pressure gradient into the pleural capillary blood. With supplemental O₂, this process is accelerated. There is no point draining what the body can safely resorb on its own.

When to admit for observation (even if "conservative"):

All SSP patients should be admitted (regardless of size) because of limited respiratory reserve
PSP patients can be discharged if asymptomatic and stable on repeat CXR at 4–6 hours

This is for tension pneumothorax only — a life-saving emergency procedure ^[1]^[2]^[16].

Parameter	Detail
Indication	Tension pneumothorax — clinical diagnosis ^[1]^[2]
Needle	14G or 16G angiocatheter ^[1]^[2]^[16]
Site (classic)	2nd ICS, mid-clavicular line ^[2]^[16]
Site (alternative — newer ATLS)	5th ICS, mid-axillary line ^[1] — preferred by some because the chest wall is thinner here and the needle more reliably reaches the pleural space
Confirmation	Listen for 'hissing sound' — air escaping under pressure ^[1]. This converts the tension PTX into an open PTX (no longer under positive pressure)
After decompression	Install a Heimlich valve to ensure one-way exit of gas ^[1], then insert a chest tube afterwards ^[1]^[16]
Adjunct	High-flow O₂ with reservoired BVM + rapid IV fluid bolus ^[16] to support the hypotensive patient

Procedure — step by step:

Identify the 2nd ICS MCL (or 5th ICS MAL) on the affected side
Clean the skin, but do NOT delay for full sterile prep if the patient is peri-arrest
Insert the 14G needle perpendicular to the chest wall, just above the rib (to avoid the neurovascular bundle in the costal groove below the rib above)
Advance until a rush of air is heard → tension relieved
Remove the needle, leave the cannula in place
Proceed immediately to chest drain insertion

Why Needle Decompression is Only Temporizing

Needle decompression does NOT definitively treat the pneumothorax. It merely converts a tension (one-way valve, positive pressure) PTX into an open PTX (atmospheric pressure). The underlying air leak persists. That is why you must always follow with a chest drain — the drain provides continuous, controlled drainage and prevents re-accumulation.

Needle aspiration (thoracocentesis): considered if > 15% lung volume ^[2]

This is the first-line intervention for symptomatic or large PSP, and can be attempted in intermediate-sized SSP.

Parameter	Detail
Indications	Symptomatic or > 2 cm PSP ^[1]; Asymptomatic 1–2 cm SSP ^[1] (less likely to succeed in SSP because underlying lung disease sustains the air leak)
Contraindications	Tension PTX (needs needle decompression + chest drain, not aspiration); bilateral PTX; haemodynamically unstable; blood in the pleural space
Equipment	14G/16G needle ^[2]; three-way stopcock; 50 mL syringe
Site	2nd anterior ICS, mid-clavicular line ^[2] (or lateral approach: 5th/6th ICS MAL ^[1])
Technique	Insert needle/angiocatheter under local anaesthesia until resistance felt (entry into pleural space) → withdraw air with syringe via three-way stopcock until resistance felt (lung re-expansion) or no more air aspirated ^[1]
Volume limit	Generally advised to aspirate < 2.5 L — if you need more, a persistent air leak is likely and aspiration alone will not resolve the PTX ^[1]
Post-procedure	Keep catheter in situ → repeat CXR at 4 hours → if lung re-expanded, remove catheter and discharge with follow-up. If failed, keep catheter with Heimlich valve then follow-up in 1–2 days, or proceed to chest drain ^[1]

Success rates:

PSP: ~60–80% success with first aspiration (good because the air leak has often sealed)
SSP: ~30–50% (lower because the underlying lung disease maintains the leak)

Why try aspiration before a chest drain? It's simpler, less painful, avoids the morbidity of a chest drain (pain, immobility, hospital admission), and many PSP patients succeed with aspiration alone. However, if aspiration fails (persistent large PTX on repeat CXR or > 2.5 L aspirated), you proceed to chest drain.

3.5 Chest Drain Insertion (Intercostal Drainage / Tube Thoracostomy)

This is the definitive acute intervention for pneumothorax when conservative management or aspiration has failed, or when the clinical scenario mandates immediate drainage.

Chest drain indications (need to know!) ^[2]:

Indication	Rationale
Bilateral PTX	Cannot observe — risk of bilateral tension physiology
Haemodynamically unstable	Requires urgent decompression regardless of size
PSP: size ≥ 2 cm or symptomatic	Large or symptomatic PSP that needs active drainage
SSP: size ≥ 1 cm or symptomatic	Lower threshold because of limited respiratory reserve
Failed needle aspiration	Aspiration unsuccessful → escalate to drain
After needle decompression of tension PTX	Definitive management after emergency temporising
Traumatic pneumothorax (most cases)	Risk of ongoing air leak from injured lung/chest wall
Ventilated patient with PTX	PPV may convert simple → tension PTX ^[1]; drain prevents re-accumulation

Parameter	Detail
Site	5th ICS, mid-axillary line (safety triangle) ^[16]
Safety triangle	Bordered anteriorly by lateral edge of pectoralis major, posteriorly by lateral edge of latissimus dorsi, inferiorly by 5th ICS, superiorly by axilla
Insert above the rib	To avoid the intercostal neurovascular bundle (nerve, artery, vein) running in the costal groove along the inferior border of each rib
Drain size	Size 24 Fr for air; 28–32 Fr for blood/pus ^[21]. However, small bore (< 14 Fr) chest drains have similar success rate as larger drains while being less painful ^[1]
Connection	Underwater seal (or Heimlich valve) without suction initially ^[1]

The underwater seal system is beautifully simple. The drain tube is connected to a bottle of sterile water, with the tube tip submerged below the water surface:

During expiration: intrapleural pressure rises (becomes less negative or positive in PTX) → air travels down the tube and bubbles through the water → exits into the atmosphere
During inspiration: intrapleural pressure becomes more negative → the water column acts as a one-way valve, preventing atmospheric air from being sucked back into the pleural space
Bubbling: Active bubbling = ongoing air leak. When bubbling stops = air leak has sealed.
Swinging: The water level in the tube oscillates ("swings") with respiration — this confirms the drain is patent and in the pleural space. Loss of swing may mean the drain is blocked, kinked, or the lung has re-expanded.

Step	Detail
Monitor	Observe for bubbling (air leak) and swinging (drain patency)
Suction	Not applied routinely initially. Low-pressure wall suction (−10 to −20 cmH₂O) may be added if lung fails to re-expand after 48 hours
CXR	Repeat after insertion to confirm drain position and lung re-expansion
Removal criteria	Lung re-expanded on CXR + no air leak (no bubbling) for ≥ 24 hours
Removal technique	Clamp drain → observe for 24h → repeat CXR → if stable, remove during expiration or Valsalva (to prevent air entry); apply occlusive dressing

Chest Drain Complications

Insertion-related:

Injury to intercostal vessels → haemothorax
Injury to lung → persistent air leak, bronchopleural fistula
Subcutaneous placement (not in pleural space)
Injury to abdominal organs if too low (liver on right, spleen on left)

In-situ complications:

Drain blockage (blood clot, kinking)
Drain displacement or falling out
Infection (empyema, wound site infection)
Subcutaneous emphysema (air tracking around drain site)
Re-expansion pulmonary oedema (RPO, 0–1%) ^[1] — see below

Re-expansion pulmonary oedema (RPO) ^[1]:

Mechanism: rapid re-expansion with restoration of blood flow into compressed capillaries → capillary damage with leakage ^[1]
Risk factors: lung collapse > 3 days, high-volume drainage, early suction use ^[1]
Signs: cough, SOB, desaturation that improves upon clamping the drain ^[1]
CXR: alveolar shadowing ^[1]
Management: supportive + clamp drain ^[1]

In penetrating chest trauma with an open wound communicating with the pleural space:

Immediate: Apply a three-sided occlusive dressing — tape on three sides, leave one side open
- Why three-sided? During inspiration, the dressing is sucked against the wound, sealing it (prevents air entry). During expiration, the open side acts as a flutter valve, allowing air to escape (prevents tension build-up).
Definitive: Formal surgical wound closure + chest drain insertion (at a separate site from the wound)

4. Definitive Management — Preventing Recurrence

Scenario	Recurrence Risk
1st PSP	10–30% at 1–5 years ^[1]
SSP	50% at 3 years ^[1]
Risk factors for recurrence	Smoking, height, age > 60 years, SSP ^[1]

The high recurrence rate — especially in SSP — is why definitive intervention is important.

4.2 Indications for Surgical Referral and Definitive Procedure

Category	Specific Indication	Rationale
Laterality	2nd ipsilateral PTX	Already had one recurrence — high risk of further
	1st contralateral PTX	Bilateral predisposition — must obliterate pleural space
	Synchronous bilateral spontaneous PTX	Cannot observe — bilateral risk
Persistent air leak	Despite 5–7 days of chest tube drainage or failed lung re-expansion ^[1]	Leak will not seal spontaneously
Haemothorax	Spontaneous haemothorax ^[1]	Risk of ongoing bleeding; may need surgical haemostasis
Specific patient groups	Professions at risk (e.g., pilots, divers) ^[1]	Risk of recurrence during occupation is dangerous
	Pregnancy ^[1]	Recurrence during labour (Valsalva) is dangerous

Pleurodesis indications (SAQ!) ^[2]:

SSP (all cases should be considered — 50% recurrence)
PSP:
- Recurrent (i.e., first contralateral, second ipsilateral)
- Synchronous bilateral PTX
- Persistent air leak (PAL)
- High-risk professions (e.g., drivers)
- Pregnancy

Must-Know: Pleurodesis Indications for SAQ

This is a favourite SAQ/short question. Remember the mnemonic "RSBPP": Recurrent PTX, Synchronous bilateral, Bronchopulmonary fistula (PAL), Professional risk, Pregnancy. Plus ALL SSP.

4.3 Surgical Treatment — The Gold Standard for Recurrence Prevention

Surgical treatment: most effective way to ↓ risk of recurrence ^[1]

Step	Purpose
Resection of any visible bullae/blebs on visceral pleura	Remove the source of the air leak
Obliterate emphysema-like changes or pleural porosities under visceral pleura	Seal microscopic leak sites
Repair of any leakage sites	Close the defect
Obliteration of pleural space by pleurectomy or pleurodesis	Prevent recurrence by eliminating the space where air can re-accumulate

Approach	Recurrence Rate	Morbidity	Details
Open thoracotomy	~1% recurrence	↑ morbidity (larger incision, more pain, longer recovery)	Gold standard for lowest recurrence; reserved for complex cases
VATS (Video-Assisted Thoracoscopic Surgery)	~5% recurrence	↓ hospital stay, ↓ morbidity	More commonly used — minimally invasive, keyhole approach

VATS is preferred in most cases because the slightly higher recurrence rate is offset by significantly lower morbidity and faster recovery. Open thoracotomy is reserved for patients with complex lung disease, failed VATS, or specific anatomical considerations.

4.4 Pleurodesis — Obliterating the Pleural Space

Pleurodesis works by deliberately irritating the pleural surfaces → triggers an intense inflammatory reaction → fibrin deposition and fibrosis → the visceral and parietal pleura fuse together → obliteration of the pleural space → air cannot re-accumulate ^[20].

Think of it like deliberately creating scar tissue between two sheets of paper to glue them together permanently.

First line in pneumothorax ^[22]:

Technique	How It Works
Mechanical abrasion with dry gauze	Surgeon physically rubs the parietal pleura with dry gauze during VATS/thoracotomy → denudes the mesothelial layer → raw surface triggers inflammation and adhesion
Laser abrasion	Similar principle — laser energy denudes the pleural surface
Pleurectomy	Surgical stripping of the parietal pleura → raw chest wall surface fuses with visceral pleura
Talc poudrage	Sterile talc powder insufflated during VATS → intense inflammatory reaction

Complications of surgical pleurodesis ^[22]:

Pain: avoid NSAIDs (because the inflammatory action is essential for pleurodesis to work — NSAIDs would blunt the very inflammation you need!) ^[22]
Recurrence: ~3% ^[22]

Preferred in recurrent malignant pleural effusion or surgically unfit patients ^[22]:

Parameter	Detail
When used	Patient refuses or is unfit for surgery; or as an adjunct to chest drain management
Agents	Talc (5 g in 100 mL NS) — i.e., magnesium silicate ^[22]; Minocycline (300 mg in 100 mL NS) ^[22]; Autologous blood: lower risk of cardiac arrest ^[22]
Data	Tetracyclines have more data for PTX; talc has more data for malignant pleural effusion ^[1]

Procedure for chemical pleurodesis ^[22]:

Adequate analgesia ± sedation — the procedure is painful
Connect chest drain → apply sclerosing agent via drain when lung is re-expanded — the pleural surfaces must be in contact for the agent to work on both surfaces
Clamp chest drain for 1–2 hours to hold the sclerosant in position, then release
If co-existing PTX / bubbling chest drain, do NOT clamp drain — instead, hang up drain to ~50 cm above patient to drain air but not the sclerosant ^[22]
Continue drainage until drain output < 150 mL/day × 2 days + CXR shows lung re-expanded ^[22]

Why NOT Clamp a Bubbling Drain During Pleurodesis?

If the chest drain is actively bubbling (air leak present), clamping it traps air → risk of tension pneumothorax. The clever solution is to elevate the drain 50 cm above the patient — air (which is lighter) rises and escapes through the elevated tubing, while the sclerosant (which is heavier, dissolved in saline) remains in the dependent pleural space by gravity ^[22].

Contraindications: parapneumonic effusion / empyema (because pleurodesis creates adhesions that would make future drainage and decortication extremely difficult) ^[22]

For persistent air leak (PAL) — defined as air leak ≥ 5 days ^[2]:

Parameter	Detail
When	After CT thorax to localise the lesion and before considering major surgery
What	Endobronchial valve (EBV): a one-way valve placed bronchoscopically into the segmental/lobar bronchus feeding the air leak
Mechanism	Intentionally collapses the lung lobe by blocking inspiratory airflow while allowing air/mucus to escape (one-way valve) → reduces air flow to the leaking site → promotes healing
Duration	Remove 6 weeks after recovery (foreign body) ^[2] — it is a temporary measure
Note	Reserved for patients who are poor surgical candidates or as a bridge to surgery

5. Other Important Management Measures

Measure	Detail	Rationale
Stop smoking	Strongly advised for all PTX patients ^[1]	Smoking is the most important modifiable risk factor; ↓ recurrence
Avoid air travel	Until ≥ 1 week after documented full resolution ^[1]	At altitude, cabin pressure drops → trapped gas expands (Boyle's Law: P₁V₁ = P₂V₂) → small residual PTX could enlarge
	Risk of recurrence only falls after 1 year → consider deferring air travel > 1 year without definitive surgical procedure, especially for SSP ^[1]	Higher-risk patients need longer observation
Avoid diving permanently	Unless bilateral pleurodesis + normal post-op lung function/CT ^[1]	Diving involves extreme pressure changes (Boyle's Law); even a tiny residual bleb could rupture → fatal pneumothorax at depth
Normal physical activity	No evidence to link recurrence with physical exertion ^[1]	Patients often ask if exercise triggered it — reassure them

Bleeding from torn pleural vessels: blunted CP angle (haemopneumothorax) → consult CTS if profuse bleeding ^[2]

When there is blood in addition to air in the pleural space:

Insert a large-bore chest drain (28–32 Fr) — smaller drains may clot off with blood
Monitor drain output — if > 200 mL/hour for 2–4 hours, or > 1500 mL total immediately, consider surgical exploration (thoracotomy or VATS)
Concurrent blood transfusion and resuscitation as needed
Consult cardiothoracic surgery (CTS) ^[2]

Clinical Scenario	Management
Tension PTX	High-flow O₂ + rapid IV fluid bolus + emergency needle decompression (14-16G, 2nd ICS MCL) → chest drain (5th ICS MAL) ^[2]^[16]
Small PSP (< 2 cm), asymptomatic	Conservative: high-flow O₂, observe 4–6h, repeat CXR, discharge if stable, FU in 2–4 weeks ^[1]
Large PSP (≥ 2 cm) or symptomatic	Needle aspiration first → if fails, chest drain ^[1]^[2]
Small SSP (< 1 cm), asymptomatic	Admit, observe, high-flow O₂, repeat CXR 24h ^[1]
SSP 1–2 cm	Needle aspiration → if fails, chest drain ^[1]
SSP ≥ 2 cm or symptomatic	Chest drain directly ^[1]^[2]
Bilateral PTX	Bilateral chest drains ^[2] — cannot observe
Traumatic PTX	Chest drain (most cases); three-sided dressing for open PTX
Iatrogenic PTX (post-CVC, etc.)	Small + asymptomatic → observe with repeat CXR; large/symptomatic → aspiration or drain
Persistent air leak ≥ 5 days	CT to localise → EBV or surgical pleurodesis ^[2]
Recurrent PTX / SSP / high-risk groups	Pleurodesis (surgical > chemical) ^[2]

Treatment	Contraindications / Cautions
Conservative observation	Contraindicated: bilateral PTX, haemodynamically unstable, SSP with ≥ 1 cm, symptomatic patient
Needle aspiration	Contraindicated: tension PTX (needs decompression + drain), bilateral PTX, haemodynamically unstable; Caution: > 2.5 L aspirated suggests persistent leak
HFNC / NIPPV	Contraindicated: positive pressure may worsen PTX ^[2]
Chest drain — clamping	Contraindicated if actively bubbling (risk of tension PTX); if needed during pleurodesis, elevate drain instead ^[22]
Pleurodesis	Contraindicated in parapneumonic effusion/empyema ^[22]; lung must be re-expanded first for surfaces to appose
NSAIDs post-pleurodesis	Avoid: inflammatory action is essential for pleurodesis success ^[22]
Air travel	Avoid until ≥ 1 week post-resolution ^[1]
Diving	Avoid permanently unless bilateral pleurodesis + normal post-op lung function and CT ^[1]

High Yield Summary

Acute Management Goals: Remove air → restore lung expansion.

O₂ therapy: Accelerates N₂ reabsorption by nitrogen washout. Avoid HFNC/NIPPV (positive pressure worsens PTX).

Tension PTX: Clinical diagnosis → immediate needle decompression (14-16G, 2nd ICS MCL or 5th ICS MAL) + high-flow O₂ + IV fluid bolus → chest drain. DO NOT wait for CXR.

PSP algorithm: Small < 2 cm + asymptomatic → observe. Large ≥ 2 cm or symptomatic → needle aspiration first (aspirate < 2.5 L) → if fails → chest drain.

SSP algorithm: Lower thresholds. < 1 cm → admit + observe. 1–2 cm → aspiration. ≥ 2 cm or symptomatic → chest drain directly. (Because SSP patients have limited reserve.)

Chest drain indications: Bilateral PTX, haemodynamically unstable, PSP ≥ 2 cm/symptomatic, SSP ≥ 1 cm/symptomatic, failed aspiration.

Chest drain removal: Lung re-expanded + no bubbling for 24 hours.

Re-expansion pulmonary oedema: Rapid re-expansion → capillary damage → leakage. RFs: collapse > 3 days, high-volume drainage, early suction. Mx: supportive + clamp drain.

Pleurodesis indications (SAQ): ALL SSP; PSP if recurrent, synchronous bilateral, PAL, high-risk profession, pregnancy.

Surgical pleurodesis: VATS (5% recurrence, ↓ morbidity) vs open thoracotomy (1% recurrence, ↑ morbidity). Involves bleb resection + pleural abrasion/pleurectomy.

Chemical pleurodesis: If unfit for surgery. Agents: talc, minocycline, autologous blood. Avoid clamping a bubbling drain — elevate 50 cm instead.

Avoid NSAIDs post-pleurodesis (blunts needed inflammation). Smoking cessation always. No diving permanently unless bilateral pleurodesis done. No flying until ≥ 1 week post-resolution.

Active Recall - Pneumothorax: Management

References

^[1] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155) ^[2] Senior notes: Maksim Medicine Notes.pdf (Section 12.6 Pleural diseases - Pneumothorax, p291) ^[16] Senior notes: Ryan Ho Critical Care.pdf (Section on Breathing emergencies, p14) ^[20] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.2.4 Pleural Effusion — pleurodesis, p229) ^[21] Senior notes: Maksim Surgery Notes.pdf (Chest drainage tube, p12) ^[22] Senior notes: Maksim Medicine Notes.pdf (Section on Pleurodesis, p294)

Complications of Pneumothorax

Complications of pneumothorax can be divided into those arising from the pneumothorax itself (disease-related) and those arising from the treatment (procedure-related). Understanding each complication from first principles helps you anticipate, recognise, and manage them early.

1. Complications of the Pneumothorax Itself

This is the most feared complication — a simple pneumothorax converting to a life-threatening emergency.

Pathophysiology: build up of pressure → compress IVC → ↓ venous return → obstructive shock & V/Q mismatch ^[2]

Aspect	Detail
Mechanism	A one-way valve develops at the air leak site — air enters the pleural space during inspiration but cannot escape during expiration. Each breath adds more air → progressive positive intrapleural pressure
Why it kills	Positive pressure compresses the IVC and kinks the great vessels → ↓ venous return → ↓ cardiac output → obstructive shock. Simultaneously, the mediastinum shifts and compresses the contralateral lung → bilateral ventilatory failure → severe hypoxaemia
Clinical features	Severe respiratory distress, distended neck veins, cyanosis, absent breath sounds + hyperresonance ipsilaterally, contralateral mediastinal deviation ^[16]
Risk scenario	Especially worrisome in diseased lungs where lung compliance is reduced. When PPV is used in the presence of pneumothorax, it may lead to tension pneumothorax ^[1]
Management	Clinical diagnosis — DO NOT wait for CXR ^[1]. Emergency needle decompression (14/16G, 2nd ICS MCL) → chest drain (5th ICS MAL) ^[16]

Tension PTX on a Ventilator

A ventilated patient who suddenly desaturates with rising airway pressures is tension PTX until proven otherwise. PPV forces air through the leak into the pleural space, and the collapsed lung cannot seal the defect ^[1]. Every ventilator breath worsens the situation. Rt endobronchial intubation (ETT too deep) can also cause Lt atelectasis + Rt tension pneumothorax ^[23].

Bleeding from torn pleural vessels: blunted CP angle (haemopneumothorax) → consult CTS if profuse bleeding ^[2]

Aspect	Detail
Mechanism	When the lung collapses, pleural adhesions (bands of fibrous tissue connecting visceral to parietal pleura) may tear. These adhesions carry blood vessels. Alternatively, rib fractures lacerate intercostal vessels or lung parenchyma
Why it matters	Blood accumulates in the pleural space alongside air → hydropneumothorax with an air-fluid level on CXR. If the bleeding is arterial (intercostal artery), it can be rapid and life-threatening
Clinical features	Features of pneumothorax PLUS signs of hypovolaemia (tachycardia, hypotension, pallor). CXR shows blunted costophrenic angle (blood) + absent lung markings above (air)
Management	Large-bore chest drain (28–32 Fr — larger to prevent clotting), blood transfusion, consult CTS ^[2]. If drain output > 200 mL/hr for 2–4 hours or > 1500 mL immediately → surgical exploration (VATS or thoracotomy)
Indication for surgery	Spontaneous haemothorax is an indication for surgical referral ^[1]

Definition: air leak ≥ 5 days ^[2]

Aspect	Detail
Mechanism	The defect in the visceral pleura or lung parenchyma fails to heal. This creates a bronchopleural fistula — a persistent communication between the bronchial tree and the pleural space. In SSP, the underlying diseased lung (e.g., emphysematous bulla, TB cavity, lung abscess) prevents healing because the tissue is structurally abnormal
Clinical recognition	Ongoing bubbling through the underwater seal drain that does not resolve after 5–7 days. The lung fails to re-expand fully despite adequate drainage
Management ^[2]	Continue chest drain with low wall suction → CT thorax to localise lesion → EBV (endobronchial valve) or pleurodesis → NEVER clamp drain (risk of tension pneumothorax) ^[2]
PAL is an indication for definitive intervention	Persistent air leak despite 5–7 days of chest tube drainage or failed lung re-expansion → surgical referral ^[1]

NEVER Clamp a Drain with Persistent Air Leak

NEVER clamp drain when there is a persistent air leak ^[2]. Clamping prevents air from escaping → air re-accumulates → risk of tension pneumothorax. The drain must remain open to allow continuous air drainage, even if bubbling is ongoing.

Aspect	Detail
Type 1 respiratory failure (hypoxaemic)	V/Q mismatch from the collapsed lung (perfused but not ventilated) → hypoxaemia with normal or low PaCO₂ (compensatory hyperventilation). This is the most common pattern in simple PTX
Type 2 respiratory failure (hypercapnic)	Occurs when remaining lung capacity is insufficient for adequate CO₂ clearance — seen in large PTX, bilateral PTX, or SSP where the non-collapsed lung is already diseased (e.g., severe COPD). SSP usually presents earlier and is disproportionately severe because of limited respiratory reserve ^[1]
Management	O₂ therapy (but avoid HFNC/NIPPV); urgent drainage if significant; mechanical ventilation if respiratory failure worsens (but remember PPV + PTX = risk of tension)

Risk of recurrence: 10–30% at 1–5 years (1st PSP), 50% at 3 years (SSP) ^[1]

Aspect	Detail
Why it recurs	The underlying structural abnormality (blebs, bullae, pleural porosity) persists even after the first episode resolves. Smoking continues to damage the lung. Without obliterating the pleural space, air can leak again from the same or different blebs
Risk factors for recurrence	Smoking, height, age > 60 years, SSP ^[1]
Clinical significance	Recurrent episodes carry the same morbidity as the first (plus cumulative psychological impact and loss of productivity). Each recurrence further increases the risk of subsequent recurrence
Prevention	Smoking cessation, pleurodesis (surgical or chemical), lifestyle modifications (avoid diving permanently, delay air travel) ^[1]
Indications for definitive surgery	2nd ipsilateral PTX, 1st contralateral PTX, synchronous bilateral PTX, persistent air leak, spontaneous haemothorax, high-risk professions, pregnancy ^[1]^[2]

This is a complication of chronicity — when the pneumothorax (or associated pleural inflammation) has been present for a prolonged period ^[2]:

Type	Mechanism	Pleural Fluid
Lung entrapment	Lung cannot expand fully because of an active disease (e.g., malignancy, active infection) encasing the visceral pleura	Exudative
Trapped lung	Lung cannot expand fully because of a remote inflammatory condition that has resolved but left behind a fibrous peel on the visceral pleura	Transudative (because there is no active inflammation; fluid forms due to increased negative pressure from the unexpanded lung pulling fluid into the pleural space)
Continuum	The active disease resolves, leaving behind the fibrosis — so lung entrapment can evolve into trapped lung over time ^[2]

Why does this matter? Pleurodesis will fail if the lung cannot re-expand (the two pleural surfaces cannot be brought into contact). These patients may require decortication (surgical stripping of the fibrous peel) to allow re-expansion.

Aspect	Detail
Mechanism	Air from the pleural space tracks through the breach in the parietal pleura into subcutaneous tissue planes. It can extend widely — from the chest wall to the neck, face, scrotum, and abdomen
Clinical features	Palpable crepitus ("rice crispy" feel) over the chest wall and neck. Can be dramatic and alarming but is usually self-limiting
When severe	Massive subcutaneous emphysema can compress the airway or impair chest wall mechanics. Look for an underlying cause (e.g., blocked chest drain, tension PTX, oesophageal perforation)
Management ^[2]	Look for and treat underlying cause (e.g., tube obstruction) → high-concentration O₂ → infraclavicular incisions (small skin incisions in the infraclavicular region allow air to escape from the subcutaneous tissue) ^[2]

Aspect	Detail
Mechanism	Air tracks along perivascular sheaths from ruptured alveoli toward the mediastinum (Macklin effect). Can also result from direct extension of a pneumothorax into the mediastinum, or from oesophageal perforation
Clinical features	Retrosternal chest pain, dyspnoea, Hamman's sign (mediastinal clicking/crunching sound synchronous with heartbeat)
CXR	Air outlining mediastinal structures (e.g., continuous diaphragm sign, ring around the artery sign)
Management	Usually self-limiting; treat the underlying cause. Monitor for extension or associated tension pneumothorax

Aspect	Detail
Mechanism	Simultaneous PTX on both sides — may occur in diffuse bullous lung disease, bilateral trauma, bilateral iatrogenic injury, or certain conditions (LAM, LCH, Birt-Hogg-Dubé syndrome)
Why dangerous	No contralateral lung to compensate → complete loss of ventilation → rapidly fatal if untreated
Management	Bilateral chest drains — cannot observe ^[2]. This is an absolute indication for chest drain insertion regardless of size. Also an indication for subsequent pleurodesis ^[2]

Aspect	Detail
Mechanism	End-stage tension pneumothorax → complete loss of venous return → cardiac arrest. The heart continues to generate electrical activity (PEA on the monitor) but has no preload → no cardiac output
Management	Part of the "4Hs and 4Ts" of cardiac arrest (Tension pneumothorax is one of the reversible causes). Bilateral needle decompression during CPR → bilateral chest drains

Complication	Mechanism
Failed procedure	Needle too short (especially in obese patients — chest wall thickness > needle length at 2nd ICS MCL), misplaced, or persistent air leak
Haemothorax	Laceration of intercostal artery if needle inserted below the rib (costal groove)
Organ perforation	Lung laceration (worsening air leak), liver injury (right side, too low), heart injury (very rare)
Infection	Introduction of bacteria → empyema

Complications of chest drainage ^[2]^[20]:

Category	Complication	Mechanism / Explanation
Puncture-related ^[2]	Pneumothorax (worsening)	Iatrogenic lung laceration during insertion
	Haemothorax / haemoptysis	Intercostal vessel or lung parenchymal laceration
	Surgical emphysema	Air tracking through the insertion site
	Organ perforation	Liver (right-sided, too low), spleen (left-sided, too low), diaphragm, stomach
	Damage to neurovascular bundle	Insertion below the rib rather than above
	Bronchopleural fistula	Drain punctures lung → persistent fistula
	Segmentation	Pockets formed by scar after each puncture ^[2] — repeated procedures create adhesions that compartmentalise the pleural space, making future drainage more difficult
Drain-related ^[2]	Re-expansion pulmonary oedema (RPO)	See Section 2.3 below
	Blockage	Blood clot or fibrin obstructing the drain lumen → loss of drainage → risk of re-accumulation
	Dislodgement	Drain falls out or migrates → loss of drainage
Infection	Empyema	Bacteria introduced during insertion or via the drain over time ^[2]^[20]
Failed procedure	Drain in wrong position	Subcutaneous placement, intra-fissural placement

This is one of the most important treatment complications to understand — it's a favourite exam question.

Re-expansion pulmonary oedema (RPO, 0–1%) ^[1]:

Aspect	Detail
Mechanism	Rapid re-expansion with restoration of blood flow into compressed capillaries → capillary damage with leakage ^[1]. When the lung has been collapsed for a prolonged period, the pulmonary capillaries become ischaemic. Upon rapid re-expansion, blood flow is suddenly restored to these damaged capillaries → increased capillary permeability → protein-rich fluid leaks into the alveoli → non-cardiogenic pulmonary oedema
Risk factors	Lung collapse > 3 days, high-volume drainage, early suction use ^[1]
Signs and symptoms	Cough, SOB, desaturation that improves upon clamping the drain ^[1]
CXR	Alveolar shadowing on the side of re-expansion (unilateral pulmonary oedema — which is unusual and should make you think of RPO) ^[1]
Management	Supportive + clamp drain ^[1]. Give O₂, consider diuretics (though this is non-cardiogenic oedema, diuretics can help reduce fluid volume), CPAP if needed. The key intervention is to slow down the re-expansion by clamping the drain. In severe cases, mechanical ventilation may be required
Prevention	Avoid draining > 1.5 L in 30 minutes for pleural effusions ^[2]; avoid early application of suction; gradual lung re-expansion

Re-expansion Pulmonary Oedema — Exam Pearl

The hallmark clue is unilateral pulmonary oedema on CXR after chest drain insertion/aspiration. This is almost always RPO. The desaturation characteristically improves upon clamping the drain (because you stop the re-expansion and prevent further capillary damage). Bilateral pulmonary oedema post-drainage is more likely fluid overload or cardiac in origin.

Complication	Mechanism
Pain	Pleural inflammation is inherently painful. Avoid NSAIDs ^[22] because the inflammatory action is essential for successful pleurodesis
Recurrence (~3% after surgical pleurodesis) ^[22]	Incomplete obliteration of the pleural space; persistent blebs on the untreated side
Fever	Expected inflammatory response to the sclerosing agent — not necessarily infection. Usually resolves within 72 hours
Empyema	Infection of the pleural space during or after the procedure
ARDS (acute respiratory distress syndrome)	Rare complication of talc pleurodesis — if talc particles are too small, they can disseminate systemically through lymphatic absorption → systemic inflammatory response → ARDS. This is why graded talc (larger particle size) is now used preferentially
Cardiac arrhythmias / cardiac arrest	Rare, associated with chemical pleurodesis agents. Autologous blood: lower risk of cardiac arrest ^[22]
Failed pleurodesis	Lung cannot re-expand (trapped lung / lung entrapment) → surfaces cannot appose → pleurodesis fails

Since CVC insertion is one of the commonest causes of iatrogenic pneumothorax, its complications warrant mention:

Insertion-related complications of CVC ^[9]:

Pneumothorax / hydrothorax / haemothorax
Air embolism — air enters the venous system during insertion (prevented by Trendelenburg positioning)
Injury of surrounding structures (e.g., thoracic duct injury, brachial plexus injury) ^[9]

Post-CVC CXR is mandatory to confirm position and rule out these complications ^[9].

Timing	Complication
Immediate (minutes)	Tension pneumothorax, cardiac arrest (PEA), massive haemopneumothorax
Early (hours–days)	Respiratory failure, subcutaneous emphysema, re-expansion pulmonary oedema, procedure complications (misplaced drain, infection)
Late (days–weeks)	Persistent air leak / bronchopleural fistula, empyema, trapped lung, failed pleurodesis
Long-term	Recurrence (10–50%), loss of lung function if recurrent, psychological impact

Pneumothorax itself frequently appears as a complication in other clinical contexts — important for exam questions:

Context	Incidence/Detail	Mechanism
CVC insertion ^[9]	Variable (0.5–6% depending on site)	Needle punctures lung apex
CT-guided lung biopsy ^[24]	Pneumothorax in 10–30% (but < 1/3 require drainage) ^[24]	Needle traverses pleura + lung parenchyma
Transbronchial lung biopsy ^[1]	2–5%	Forceps tears visceral pleura from within
Mechanical ventilation (barotrauma) ^[1]^[2]	Variable; higher in ARDS, high PEEP	Alveolar overdistension → rupture → air tracks to mediastinum and pleura
Thoracocentesis ^[20]	2–15% ^[20]	Needle punctures lung during pleural aspiration
Tuberculosis ^[25]	1%	Rupture of peripheral cavity or subpleural caseous focus with liquefaction into pleural space ^[25]
COPD ^[1]	Most common cause of SSP (50–70%)	Rupture of emphysematous bullae
Lung abscess / empyema ^[1]	Rare	Rupture into bronchus → bronchopleural fistula + pyopneumothorax ^[26]
Rheumatoid pulmonary nodules ^[27]	Rare	Nodules may rupture and result in pneumothorax ^[27]
Laparoscopic surgery ^[10]	Rare	Pneumoperitoneum-related: CO₂ tracks through congenital diaphragmatic defects or along aortic/oesophageal hiatus ^[10]
Post-thyroidectomy ^[28]	Rare	Injury to trachea / pneumothorax during dissection near trachea ^[28]
Percutaneous nephrostomy ^[29]	Rare (< 1%)	Upper pole puncture may traverse the pleural reflection at the posterior costophrenic sulcus

Complication	Mechanism in Brief	Key Clinical Clue	Management
Tension PTX	One-way valve → positive pressure	↓ BP + ↑ JVP + absent BS + tracheal deviation	Needle decompression → chest drain
Haemopneumothorax	Torn pleural vessels / intercostal vessels	Blunted CP angle on CXR + hypovolaemia	Large-bore drain + CTS referral
Persistent air leak	Bronchopleural fistula, underlying lung disease	Bubbling > 5–7 days	CT → EBV or surgery; NEVER clamp
RPO	Rapid re-expansion → capillary damage	Unilateral oedema + desaturation that improves on clamping	Supportive + clamp drain
Recurrence	Persistent structural abnormality (blebs/bullae)	Same presentation as first episode	Pleurodesis / surgery
Subcutaneous emphysema	Air tracks into subcutaneous tissue	Palpable crepitus	Treat cause + O₂ + infraclavicular incisions
Trapped lung	Fibrous peel from chronic inflammation	Lung fails to re-expand despite adequate drainage	Decortication
Empyema	Infection of pleural space (primary or iatrogenic)	Fever + purulent drain output	Antibiotics + drain + possible decortication

High Yield Summary

Tension pneumothorax = most feared complication. One-way valve → positive pressure → IVC compression → obstructive shock. Clinical diagnosis — do NOT wait for CXR. Needle decompression → chest drain.

Haemopneumothorax = torn pleural vessels. Blunted CP angle + hypovolaemia. Large-bore drain + CTS consult. Surgery if > 200 mL/hr output.

Persistent air leak (PAL) = air leak ≥ 5 days. CT to localise → EBV or surgical pleurodesis. NEVER clamp a bubbling drain.

Re-expansion pulmonary oedema (RPO) = rapid re-expansion → capillary damage. RFs: collapse > 3 days, high-volume drainage, early suction. Key sign: unilateral pulmonary oedema + desaturation improving on clamping drain. Mx: supportive + clamp drain.

Recurrence = 10–30% (PSP), 50% at 3 years (SSP). RFs: smoking, height, age > 60, SSP. Indications for definitive surgery: 2nd ipsilateral, 1st contralateral, bilateral, PAL, haemothorax, high-risk profession, pregnancy.

Subcutaneous emphysema = air in soft tissue. Treat underlying cause + O₂ + infraclavicular incisions if severe.

Trapped lung / lung entrapment = fibrous peel prevents re-expansion → pleurodesis will fail → need decortication.

Chest drain complications: Puncture-related (haemothorax, organ perforation, NVB damage, bronchopleural fistula, segmentation), drain-related (RPO, blockage, dislodgement), infection (empyema).

Avoid NSAIDs after pleurodesis (need the inflammation). Avoid HFNC/NIPPV in PTX (positive pressure worsens it).

Active Recall - Pneumothorax: Complications

References

^[1] Senior notes: Ryan Ho Respiratory.pdf (Section 3.7 Pneumothorax, p151–155) ^[2] Senior notes: Maksim Medicine Notes.pdf (Section 12.6 Pleural diseases - Pneumothorax, p291; Complications p296) ^[9] Senior notes: Ryan Ho Fluids and Nutrition.pdf (Section on TPN complications, p11) ^[10] Senior notes: Maksim Surgery Notes.pdf (Section 1.6 Post-op complications, p28; Section 2.1 Trauma, p42) ^[16] Senior notes: Ryan Ho Critical Care.pdf (Section on Breathing emergencies, p14) ^[20] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.2.4 Pleural Effusion - thoracentesis complications, p229) ^[22] Senior notes: Maksim Medicine Notes.pdf (Section on Pleurodesis, p294) ^[23] Senior notes: Ryan Ho Critical Care.pdf (Section on ETT malposition, p10) ^[24] Senior notes: Ryan Ho Diagnostic Radiology.pdf (Section 7.1 Interventional Radiology - lung biopsy complications, p80) ^[25] Senior notes: Ryan Ho Respiratory.pdf (Section on pulmonary TB complications, p76) ^[26] Senior notes: Ryan Ho Respiratory.pdf (Section 3.1.2.6 Parapneumonic Effusion and Empyema - complications, p72) ^[27] Senior notes: Ryan Ho Respiratory.pdf (Section 3.3.6 Respiratory Manifestations of Rheumatic Diseases - RA, p128) ^[28] Senior notes: Maksim Surgery Notes.pdf (Section on thyroidectomy complications - post-op dyspnoea DDx, p198) ^[29] Senior notes: Ryan Ho Diagnostic Radiology.pdf (Section on Percutaneous Nephrostomy complications, p83)

Pneumothorax

1. Definition

2. Epidemiology

Incidence

Demographics

Hong Kong context

3. Risk Factors

4. Anatomy and Function of the Pleural Space

Pleural Anatomy

Pleural Pressure Physiology

Air Reabsorption from the Pleural Space

Surface Anatomy for Procedures

5. Etiology (with Focus on Hong Kong)

5.1 Spontaneous Pneumothorax

Primary Spontaneous Pneumothorax (PSP) — no underlying lung disease [1][2]

Secondary Spontaneous Pneumothorax (SSP) — underlying lung disease present [1][2]

5.2 Traumatic Pneumothorax

Penetrating Injury [4][6]

Blunt Injury [4][7]

Blast Injury [4]

5.3 Iatrogenic Pneumothorax [1][2]

6. Classification

6.1 By Etiology

6.2 By Pathophysiology (Type of Pleural Communication)

6.3 By Size (BTS Guidelines 2023)

7. Pathophysiology (Detailed)

7.1 Mechanism of Lung Collapse

7.2 Physiological Consequences

7.3 Tension Pneumothorax — The Emergency [1][2]

8. Clinical Features

8.1 Symptoms (with Pathophysiological Basis)

8.2 Signs (with Pathophysiological Basis)

Small Pneumothorax

Large Pneumothorax

Tension Pneumothorax Signs [1][2]

Additional Signs in Specific Scenarios

8.3 CXR Features [1][2][11]

Erect PA CXR (Diagnostic Standard)

Supine CXR (Trauma Setting — Easily Missed!) [11]

Size Assessment on CXR

Associated CXR Findings

9. Special Populations and Scenarios

9.1 Neonatal Pneumothorax [8]

9.2 Trauma Setting [4][6][7]

9.3 Catamenial Pneumothorax

9.4 Pneumothorax in Pregnancy

10. Clinical Approach Summary

Active Recall - Pneumothorax: Definition to Clinical Features

References

1. Why Differential Diagnosis Matters for Pneumothorax

2. Differential Diagnosis of Acute Chest Pain (Where Pneumothorax Sits)

Potentially severe or life-threatening causes [13][14]

Relatively benign causes [13][14]

3. Differential Diagnosis of Acute Dyspnoea (Where Pneumothorax Sits)

4. Differential Diagnosis Specific to Physical Signs

4.1 Unilateral Absent Breath Sounds — PTX vs Pleural Effusion vs Consolidation

4.2 Tension PTX vs Cardiac Tamponade (Obstructive Shock DDx)

5. Differential Diagnosis by Context

5.1 Post-Procedure (Iatrogenic)

5.2 Trauma Context [4][6][7][10]

5.3 Neonatal Context [8]

6. Systematic DDx Decision Framework (Mermaid)

7. Key Differentiating Clues — Rapid Reference Table

8. Common Exam Traps

Active Recall - Differential Diagnosis of Pneumothorax

1. Diagnostic Criteria — What Confirms a Pneumothorax?

1.1 Clinical Diagnosis (No Imaging Required)

1.2 Imaging-Confirmed Diagnosis (All Non-Tension PTX)

1.3 Size Classification (BTS 2023 / HK Practice)

2. Diagnostic Algorithm

3. Investigation Modalities — Detailed Guide

3.1 Chest X-Ray (CXR) — First-Line Investigation

Key CXR Findings in Pneumothorax

Erect CXR vs Supine CXR

Special CXR Techniques

CXR Quality Assessment Checklist [19]

3.2 CT Thorax — Gold Standard

Indications for CT in Pneumothorax

CT Protocol in Trauma [10][11]

CT Findings