About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Primary spontaneous: no known lung disease, typically tall, thin, young males. Secondary: underlying lung disease (COPD, asthma, CF)
- Diagnosis: CXR (visible visceral pleural line, absent lung markings peripherally)
- BTS algorithm for primary: if rim of air <2 cm and not breathless → conservative; if ≥2 cm or breathless → aspiration first, then chest drain if fails
- Secondary: if >50 years and rim ≥2 cm or breathless → chest drain. If 1–2 cm → aspiration. If <1 cm → observation with O₂
- Tension pneumothorax: clinical diagnosis — do NOT delay for CXR. Treat with immediate needle decompression (2nd ICS MCL) then chest drain
Overview
A pneumothorax occurs when air enters the pleural space — the potential space between the visceral and parietal pleura — causing lung collapse. Primary spontaneous pneumothorax (PSP) occurs in patients without clinically apparent lung disease, typically due to rupture of subpleural blebs. Secondary spontaneous pneumothorax (SSP) occurs as a complication of underlying lung disease (most commonly COPD). Traumatic pneumothorax results from penetrating or blunt chest injury or iatrogenic causes (central line insertion, lung biopsy, positive pressure ventilation). Tension pneumothorax is a life-threatening emergency where a one-way valve mechanism leads to progressive air accumulation, mediastinal shift, and cardiovascular compromise.
Epidemiology
Primary spontaneous pneumothorax incidence is approximately 18–28 per 100,000 per year in men and 1.2–6 per 100,000 in women. Peak incidence is in tall, thin males aged 20–30 years. Smoking increases the risk 20-fold. Secondary spontaneous pneumothorax occurs most commonly in COPD patients over 60, with higher morbidity and mortality due to diminished respiratory reserve. Recurrence is common: approximately 30% for PSP and 40–50% for SSP after the first episode.
Clinical Features
Symptoms
Sudden onset pleuritic chest pain — often unilateral
Acute breathlessness — more severe in secondary pneumothorax
May be mild or asymptomatic in small primary pneumothorax
Signs
Reduced breath sounds on the affected side
Hyperresonant percussion on the affected side
Reduced chest expansion
Tracheal deviation AWAY from the affected side (tension pneumothorax)
Distended neck veins / raised JVP (tension)
Hypotension and tachycardia — obstructive shock (tension)
Subcutaneous emphysema (crepitus under skin)
Investigations
First-line
Chest X-ray (erect, inspiratory)Visible pleural line with absent lung markings beyond it. Measure size: distance from lung edge to chest wall at the hilum. >2 cm = large pneumothorax (BTS definition)
Second-line
ABGIn SSP or if significant breathlessness — may show hypoxia and/or hypercapnia
CT thoraxIf diagnostic uncertainty (e.g. differentiating large bulla from pneumothorax in COPD) or planning surgical intervention
Specialist
CT thorax (for surgical planning)Bilateral disease, recurrent pneumothorax, persistent air leak — assessing for bullous disease or pleurodesis planning
Management
BTS Pleural Disease Guidelines 20231
Tension pneumothorax (clinical diagnosis — do NOT wait for CXR)
- Immediate needle decompression: large-bore cannula (14–16G) into 2nd intercostal space, midclavicular line
- Followed by chest drain insertion (5th ICS, mid-axillary line, safe triangle)
- High-flow oxygen
- This is a clinical diagnosis — tracheal deviation, absent breath sounds, cardiovascular compromise
2
Primary spontaneous pneumothorax (BTS algorithm)
- Small (<2 cm) and NOT breathless → conservative management: observe for 4 h, discharge with safety-net advice, review in 2–4 weeks
- Large (≥2 cm) OR breathless → needle aspiration (2nd ICS MCL, 16–18G cannula, aspirate up to 2.5 L)
- If aspiration successful (lung re-expanded, symptoms improved) → observe for 4 h then discharge
- If aspiration fails → insert chest drain (small-bore 8–14 Fr Seldinger)
3
Secondary spontaneous pneumothorax
- Small (<1 cm) and not breathless → admit, observe with high-flow O₂ (accelerates reabsorption)
- 1–2 cm → aspiration first; if fails → chest drain
- Large (>2 cm) OR breathless → chest drain (do not attempt aspiration alone in large SSP)
- All SSP patients should be admitted due to lower respiratory reserve
4
Ongoing management and recurrence prevention
- Advise smoking cessation (reduces recurrence risk)
- Avoid flying until confirmed resolution (typically 1 week post-CXR resolution for PSP, 6 weeks for SSP)
- Avoid diving permanently unless bilateral definitive pleurectomy performed
- Recurrent pneumothorax or persistent air leak: refer thoracic surgery for VATS pleurodesis or pleurectomy
Complications
- Tension pneumothorax: Life-threatening — progressive mediastinal shift, reduced venous return, cardiovascular collapse
- Recurrence: ~30% PSP, ~50% SSP — indication for definitive surgical management after second episode
- Persistent air leak: >5–7 days of ongoing bubbling in chest drain → may require surgical intervention
- Re-expansion pulmonary oedema: Rare but serious complication after rapid re-expansion of a collapsed lung
- Empyema: Rare — secondary infection of the pleural space
UKMLA Exam Tips
- 1Tension pneumothorax is a CLINICAL diagnosis — tracheal deviation, absent breath sounds, shock. Do NOT wait for CXR
- 2Needle decompression: 2nd ICS midclavicular line. Chest drain: 5th ICS mid-axillary line (safe triangle)
- 3BTS defines "large" pneumothorax as >2 cm from lung edge to chest wall at the hilum
- 4Primary: try aspiration first. Secondary: drain if large or breathless — these patients have less respiratory reserve
- 5No flying until resolution confirmed. No diving EVER unless bilateral surgical pleurectomy
- 6If you see a tall, thin young man with sudden pleuritic chest pain → pneumothorax until proven otherwise
practicetest your knowledge on pneumothoraxApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — respiratory and beyond.
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