Pneumothorax (including tension pneumothorax)

A pneumothorax is air in the pleural space, and although most are simple, one form — tension pneumothorax — is among the few genuinely immediately fatal emergencies in medicine, killed by the one-way-valve physiology that traps air in the chest until it obstructs venous return and the circulation arrests. The Fellowship candidate must recognise tension as a clinical diagnosis and decompress before any imaging, then apply the size-based management to the spontaneous pneumothorax and the correct landmarks to the chest drain.[1]

Definition and classification

A pneumothorax is air in the pleural space between the visceral and parietal pleura, which collapses the lung toward the hilum. It is classified by cause. A primary spontaneous pneumothorax arises in a patient with no underlying lung disease — typically a tall, thin, young, male smoker, occasionally with a family history or a connective-tissue disorder such as Marfan syndrome. A secondary spontaneous pneumothorax complicates underlying lung disease, most commonly chronic obstructive pulmonary disease, but also asthma, cystic fibrosis, interstitial lung disease, lymphangioleiomyomatosis, and Pneumocystis pneumonia. A traumatic pneumothorax follows blunt or penetrating injury and an iatrogenic one follows a procedure (a central venous catheter, a biopsy, positive-pressure ventilation). The lethal form is tension pneumothorax, in which a one-way valve traps air on each inspiration. [1]

The four broad categories have distinct demographics, mechanisms, and risks, and the table below frames the comparison the examiner expects. [1]

Risk factors and aetiology in detail

The strongest modifiable risk factor for a primary spontaneous pneumothorax is cigarette smoking — the relative risk rises roughly in proportion to cumulative dose, and the lifetime incidence in smokers is about twelve per cent versus under one per cent in non-smokers. The classic phenotype is the tall, thin, young male whose greater pleural pressure gradient at the apex predisposes the subpleural bleb to rupture. A family history and the connective-tissue disorders — Marfan syndrome, homocystinuria, Loeys-Dietz, α₁-antitrypsin deficiency, and Birt-Hogg-Dubé syndrome — each carry an elevated baseline risk and should be named in the viva. Catamenial pneumothorax, occurring within 72 hours of menses in women aged 30–40 with thoracic endometriosis, is a recurring secondary cause worth naming. For the secondary pneumothorax the underlying disease is the driver: COPD dominates, but cystic fibrosis, pulmonary Langerhans-cell histiocytosis, lymphangioleiomyomatosis (almost exclusively young women), idiopathic pulmonary fibrosis, tuberculosis, lung abscess, and Pneumocystis jirovecii pneumonia (classically pneumocystis in an HIV-positive patient on prophylactic trimethoprim-sulfamethoxazole, often bilateral and recurrent) are all high-yield. Iatrogenic causes cluster around the procedures that breach the pleura — central venous catheterisation (subclavian more than internal jugular), transthoracic needle biopsy, thoracentesis, transbronchial biopsy, barotrauma from positive-pressure ventilation, and cardiopulmonary resuscitation.[5]

Pathophysiology — why tension kills

A pleural defect lets air enter the pleural space, and the elastic recoil of the lung collapses it. In tension pneumothorax a one-way valve admits air on inspiration but prevents its escape, so the intrapleural pressure climbs with each breath. The rising pressure shifts the mediastinum to the contralateral side, kinks and compresses the great veins and the contralateral lung, and obstructs the venous return to the heart. The result is obstructive shock and, untreated, cardiac arrest. The single intervention that reverses this — releasing the trapped air by a needle or a drain — is therefore both diagnostic and therapeutic, and it must not wait for a radiograph. [1]

Clinical presentation

A spontaneous pneumothorax presents with sudden pleuritic chest pain and breathlessness. A small primary pneumothorax may be only minimally symptomatic; a secondary one, in a patient with little respiratory reserve, can be life-threatening from the outset. Tension pneumothorax presents with severe respiratory distress and the obstructive-shock constellation: hypoxia, hypotension, a distended jugular venous pulse, a deviated trachea (a late sign), reduced air entry and a hyperresonant percussion note on the affected side, and tachycardia. In the ventilated patient the clues are a rising peak airway pressure, hypoxia, and hypotension, and a tension must be assumed in any ventilated patient who deteriorates with high airway pressures. [1]

Differential diagnosis

The sudden pleuritic pain and breathlessness have a differential, and the chest radiograph (or the bedside ultrasound) resolves it — except in tension, which is clinical. [1]

Investigations and the targets

For the stable patient the erect chest radiograph is the standard: it shows the visceral pleural line with absent lung markings beyond it, and the size is graded by the interpleural distance at the hilum (a small pneumothorax has a rim under 2 cm, a large one 2 cm or more).[1] The bedside ultrasound (absent lung sliding, the lung-point sign) is rapid and is used in the trauma and the undifferentiated-dyspnoea patient. A computed-tomography scan is reserved for the complex, loculated or small pneumothorax, for the secondary case, and — critically — to distinguish a giant bulla from a pneumothorax before any drainage. An arterial blood gas quantifies the hypoxia in the unwell patient. In suspected tension, none of these is performed first — the diagnosis is clinical and the treatment is immediate decompression.

Immediate management — tension first

Tension pneumothorax is decompressed at once. The preferred site is the fifth intercostal space, anterior to the mid-axillary line, with a device long enough to reach the pleura, because the chest wall at this site is on average thinner than at the classical second-intercostal mid-clavicular site and a standard short intravenous cannula often fails to enter the pleural space.[2] Decompression is followed at once by a formal chest drain (the needle is a bridge, not a treatment). High-flow oxygen is given throughout.

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Needle decompression — step by step (FlowSteps)

Why the 5th intercostal space mid-axillary displaced the 2nd space mid-clavicular

The classical teaching placed the decompression cannula at the second intercostal space, mid-clavicular line. Anatomical and clinical evidence has shifted the recommended site to the fifth intercostal space, anterior to the mid-axillary line.[2][4] The reasons are shown below.

[1] [1] [1]

Definitive management — the spontaneous pneumothorax by size

The spontaneous pneumothorax is managed by size and symptoms.[1]

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The chest drain (tube thoracostomy) is inserted by blunt dissection (or a Seldinger technique for a small-bore drain) in the safe triangle at the fourth or fifth intercostal space, anterior axillary line, directed toward the apex, and connected to an underwater seal. The British Thoracic Society accepts a small-bore (8 to 14 French pigtail) drain for most spontaneous pneumothoraces, reserving a large-bore (24 to 32 French) drain for the traumatic, the haemothorax, and the persistent air leak. A Heimlich flutter valve is used for transfer. [1]

The insertion is performed under strict asepsis with local anaesthesia — lidocaine 1 per cent, with adrenaline 1:200,000 to a maximum of about 3 mg per kilogram, or 7 mg per kilogram without adrenaline — infiltrated generously down to and across the pleura at the chosen site, with conscious sedation (midazolam 1 to 2 mg intravenously, or fentanyl 50 to 100 micrograms) for the larger drain if the patient is stable. The steps confirm the safe triangle (bordered by the anterior edge of latissimus dorsi, the lateral border of pectoralis major, and a line above the fifth intercostal space, below the nipple and the axilla); a 2 to 3 cm incision is made along the upper border of the rib to spare the intercostal nerve and vessels that run in the subcostal groove; a blunt clamp dissects through the intercostal muscles to and through the pleura; a gloved finger confirms entry and sweeps adhesions; the drain is advanced toward the apex; the tube is connected to the underwater seal; and it is secured and dressed. The underwater seal allows air and fluid to leave but not to return, and swinging (tidalling) of the water column with respiration confirms the intrapleural position. Aftercare is analgesia, a confirmatory radiograph, and observation for a persistent air leak or a re-expansion oedema. A persistent air leak beyond four to five days, or a failure of the lung to re-expand, prompts a thoracic-surgical referral for a suspected bronchopleural fistula and definitive closure, since a chronic leak will not resolve with continued drainage alone. [1]

Simple aspiration — step by step (FlowSteps)

[1] [1] [1] [1]

Recurrence is common — about 30 per cent after a first primary pneumothorax — so recurrence-prevention (medical or surgical pleurodesis, or VATS) is offered after a second event or in high-risk patients such as aviators and divers. [1]

Complications and pitfalls

The complications include infection and empyema, a persistent air leak or bronchopleural fistula, pain, and re-expansion pulmonary oedema, which follows the too-rapid re-expansion of a large, long-standing pneumothorax and is avoided by draining slowly or incrementally in that setting. The pitfalls are the dangerous inverse of the management: waiting for a radiograph in a suspected tension; using a standard short cannula for decompression; mistaking a giant bulla for a pneumothorax and draining it (creating a fistula); draining a chronic pneumothorax too quickly; and not warning the patient about recurrence and the aviation and diving restrictions. [1]

[1] [1] [1] [1] [1] [1] [1] [1]

Prognosis and disposition

Most primary spontaneous pneumothoraces resolve with observation, aspiration, or a drain; recurrence is around 30 per cent, lower after pleurodesis. A patient with a drain is admitted; a small primary pneumothorax managed by observation may be discharged with early follow-up and clear return precautions. Every patient receives explicit advice about the lifetime aviation and diving restrictions after a pneumothorax. [1]

Special populations

Chronic obstructive pulmonary disease is the commonest cause of a secondary pneumothorax and the commonest source of a bulla-mimic — so a CT is sought before drainage when the radiograph is uncertain. Pregnancy modifies the drainage approach. Aviators and divers are grounded for life after a pneumothorax because a recurrence at altitude or depth is catastrophic. Cystic fibrosis and lymphangioleiomyomatosis are high-risk secondary causes. [1]

Evidence and regional guidelines

The contemporary framework is the British Thoracic Society pleural disease guideline[1]; the decompression-site and device-choice evidence, which has moved away from the classical second-intercostal mid-clavicular site toward the fifth-intercostal anterior-axillary site with a longer device, is summarised in recent meta-analysis.[2] The drug and procedural choices are broadly global; the local trauma protocol governs the decompression device and the drain size.

Exam practice

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Exam pearls

• Tension is clinical — hypotension, raised JVP, absent breath sounds, hyperresonance — decompress before any imaging.
• Decompress at the fifth intercostal space, anterior to mid-axillary, with a device long enough (≥5 cm) to reach the pleura; the 2nd ICS mid-clavicular site has largely been abandoned.
• PSP small (<2 cm) and asymptomatic: observe ± oxygen; large (≥2 cm) or symptomatic: aspirate first (16G, ≤2.5 L), then drain if it fails; SSP: usually drain outright.
• High-flow oxygen accelerates nitrogen resorption ~4-fold — but avoid in CO₂-retaining COPD.
• Confirm a suspected bulla with CT before draining — draining a bulla creates a bronchopleural fistula.
• Safe triangle, fourth or fifth intercostal space, anterior axillary line, upper border of the rib, for a chest drain.
• Beware re-expansion oedema — drain a long-standing collapse slowly; aspirate ≤2 L; stop for chest tightness/cough.
• Aviation and diving: lifetime grounding after a pneumothorax — a recurrence at altitude or depth is catastrophic.
• Recurrence ≈30% after a first PSP — offer pleurodesis/VATS after a second event or for high-risk occupations.
• The underwater seal should swing — no swing = blocked, kinked, malpositioned, or fully re-expanded; continuous bubbling = significant air leak.
• Never clamp a bubbling chest drain in the ED — it recreates a tension; clamp only on respiratory-surgical instruction.
• Aspirate up to 2.5 litres — sudden chest tightness, cough, or re-expansion pain means stop.
• The ventilated patient who deteriorates with rising peak airway pressure has a tension until proven otherwise — decompress on suspicion.
• Subclavian CVC > internal jugular for iatrogenic pneumothorax — post-procedure erect CXR is mandatory.
• PJP (Pneumocystis) in HIV causes bilateral, recurrent, refractory pneumothoraces — early surgical referral.
• Catamenial pneumothorax: recurrent right-sided PSP in a woman within 72 h of menses — think thoracic endometriosis. [1]

Red flags

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References

1. [1]MacDuff A, Arnold A, Harvey J, et al. Management of spontaneous pneumothorax: British Thoracic Society Pleural Disease Guideline 2010 Thorax, 2010.PMID 20696690
2. [2]Ahmad SJS, Clark ATM, Momin R, et al. Meta-analysis of the optimal needle length and decompression site for tension pneumothorax and consensus recommendations on current ATLS and ETC guidelines World J Emerg Surg, 2025.PMID 40383767
3. [3]Roberts ME, Rahman NM, Maskell NA, et al. British Thoracic Society Guideline for pleural disease Thorax, 2023.PMID 37553157
4. [4]Laan DV, Vu TD, Thiels CA, et al. Chest wall thickness and decompression failure: A systematic review and meta-analysis comparing anatomic locations in needle thoracostomy Injury, 2016.PMID 26724173
5. [5]Tschopp JM, Bintcliffe O, Astoul P, et al. ERS task force statement: diagnosis and treatment of primary spontaneous pneumothorax Eur Respir J, 2015.PMID 26113675