Pneumothorax — Viva

Q1: Definition and classification (2 min)

"Define a pneumothorax and classify it."

• Definition: air in the normally negative-pressure pleural space (~-5 cmH₂O end-expiration); the loss of mechanical coupling lets the lung's elastic recoil collapse it.
• Primary spontaneous (PSP): no underlying disease; tall, thin, young male smoker; ruptured apical subpleural bleb.
• Secondary spontaneous (SSP): underlying disease — COPD (commonest), asthma, CF, Pneumocystis, TB, LAM, sarcoidosis.
• Traumatic: blunt (rib fracture) or penetrating; often haemopneumothorax.
• Iatrogenic: central line, transthoracic biopsy, mechanical ventilation/barotrauma (Macklin effect).
• Tension: a complication of any type — one-way valve raising intrathoracic pressure; clinical diagnosis.
• Variants: hydropneumothorax, haemopneumothorax, pyopneumothorax; catamenial (right-sided, perimenstrual, diaphragmatic endometriosis).

Q2: Pathophysiology and why tension is dangerous (2 min)

"Explain the mechanism, including the haemodynamics of tension pneumothorax."

• Air abolishes the negative intrapleural pressure → lung collapses → V/Q mismatch and shunt → hypoxaemia (no diffusion defect).
• High-flow oxygen lowers alveolar/venous nitrogen partial pressure → nitrogen washout widens the reabsorption gradient (~4× faster than room air).
• Tension: one-way valve traps air → intrapleural pressure above atmospheric → lung collapses to hilum, mediastinum and trachea pushed away, diaphragm depressed, great veins compressed → venous return and cardiac output fall → hypotension, tachycardia, distended neck veins.
• Pitfall: in the ventilated patient the textbook triad is often absent — rising airway pressure + hypotension + hypoxia may be the only clues.

Q3: Clinical and bedside assessment (2 min)

"How do you examine a suspected pneumothorax, and how do you localise the side?"

• Inspect: reduced expansion, asymmetry, subcutaneous emphysema.
• Palpate: tracheal position (deviated away in tension/large effusion; towards in collapse/fibrosis); apex beat.
• Percuss: hyper-resonance (vs dullness in effusion/consolidation).
• Auscultate: reduced breath sounds and reduced vocal resonance.
• Side-localisation rule: hyper-resonance + deviation away = pneumothorax (tension if unwell); dullness + deviation away = effusion; dullness + deviation towards = collapse.
• Lung ultrasound: absent lung sliding + absent B-lines; the lung point is highly specific.

Q4: Investigations and sizing (2 min)

"What tests, and how do you size a pneumothorax?"

• Erect PA CXR — pleural line with absent lung markings beyond.
• BTS size cut: interpleural distance at the hilum — under 2 cm = small; 2 cm or more = large (~50%).
• CHEST cut: apex-to-cupola 3 cm or more = large (classifies more as large).
• CT — gold standard; for small/loculated/traumatic, to distinguish a bulla from a pneumothorax, and surgical planning.
• Pitfalls: supine film — air anterior, deep sulcus sign, easily missed; skin-fold artefact (line extends beyond the thorax, vessels visible beyond).

Q5: Management (3 min)

"Walk me through the BTS management of a spontaneous pneumothorax, and of tension pneumothorax."

• Small PSP (under 2 cm), asymptomatic — observe + high-flow oxygen; discharge with safety-net, review 2 to 4 weeks.
• Large or symptomatic PSP — simple aspiration: 16G cannula, 2nd ICS MCL, aspirate up to 2.5 L; if fails → small-bore (8 to 14 Fr) Seldinger drain through the safe triangle (4th to 5th ICS, anterior mid-axillary line) on underwater seal.
• SSP (any size) — admit + chest drain (small-bore usually; large-bore for haemothorax/copious air); conservative management is unsafe.
• Underwater seal: swinging/tidalling = patent; bubbling = air leaving; continuous bubbling = ongoing air leak (bronchopleural fistula).
• Persistent air leak (>3 to 5 days) — low-pressure suction (-10 cmH₂O) then surgical referral.
• Surgical pleurodesis (VATS) — indications: second ipsilateral PSP, first contralateral PSP, persistent air leak, SSP at first presentation, bilateral, high-risk occupations. Chemical alternative: talc slurry / minocycline (Chen 2013 Lancet RCT).
• Tension — clinical diagnosis; decompress BEFORE imaging. Needle decompression (2nd ICS MCL or 5th ICS mid-axillary line, large-bore/longer fenestrated catheter), then definitive chest drain; high-flow oxygen, IV access, treat shock.
• Discharge: stop smoking; no flying until CXR clear; no diving without surgery; follow-up CXR 2 to 4 weeks.

Q6: Pitfalls and special situations (2 min)

"Give me the classic pitfalls and how pneumothorax differs in special populations."

• Pitfalls: draining a bulla as a pneumothorax (→ bronchopleural fistula; CT if doubt); waiting for a CXR in tension; inserting a drain below a rib (into the neurovascular bundle — always go above); over-rapid re-expansion → re-expansion pulmonary oedema; missing a small traumatic pneumothorax supine (deep sulcus sign).
• Ventilated/ICU patient — high risk of rapid tension; drain proactively; use lung-protective ventilation (6 mL/kg, plateau under 30 cmH₂O) after barotrauma.
• Catamenial — woman, right-sided, within 72 h of menses; VATS pleurodesis + diaphragmatic repair + hormonal suppression.
• Neonate — sudden deterioration on CPAP/ventilation (meconium aspiration/RDS); 22 to 24G cannula decompression then small drain, equipment sized to weight.
• Anticoagulated — risk of haemothorax with drainage; reverse anticoagulation (warfarin: vitamin K + PCC) if not a true emergency; tension overrides everything.
• Recurrence — PSP ~30%, SSP higher; pleurodesis after second event.