Pulmonary Barotrauma

Pulmonary barotrauma is lung injury from pressure change. In diving it is mostly overexpansion on ascent, which causes pneumothorax, pneumomediastinum, subcutaneous emphysema and arterial gas embolism. Barotrauma of descent (lung squeeze) is uncommon.

Mechanism. Gas in the lungs expands as ambient pressure falls on ascent. If gas cannot escape, for example in breath holding, glottic closure or air trapping, alveoli overdistend and rupture. A pressure difference of 70 to 100 mmHg can rupture alveoli, equal to about 1 metre of water.

Risk factors. Panic ascent, breath holding, asthma, chronic obstructive disease, cysts and blebs, scarring, infection and mechanical ventilation.

Related events. Hyperbaric chamber, submarine escape, compressed air work, and positive pressure ventilation with high pressures.

Severity. Pneumothorax can become tension and cause arrest; arterial gas embolism needs urgent recompression.

Pathophysiology.

Overdistension tears alveolar walls. Gas tracks along bronchovascular sheaths into the mediastinum, neck, subcutaneous tissue or pleura, or enters torn pulmonary veins as arterial emboli.

Descent causes lung squeeze with congestion and haemorrhage when volume falls under residual volume, typically in deep breath hold diving.

• Retrosternal chest pain, dyspnoea, cough and hoarseness.
• Subcutaneous crepitus in the neck and chest, a crunching sound with the heartbeat (Hamman sign), and changed voice.
• Pneumothorax: pleuritic pain, reduced breath sounds, hypoxia, and in tension, shock and tracheal shift.
• Haemoptysis after squeeze, and neurological features if embolism occurs.

Red flags.

• Shock, hypoxia, tracheal deviation (tension pneumothorax).
• Any neurological symptom after surfacing (arterial gas embolism).

• Dive history and symptoms; examination of chest, neck and neurological state.
• Chest radiograph, upright in expiration when possible; ultrasound for pneumothorax at the bedside.
• CT chest for pneumomediastinum, blebs and predisposing lung disease once stable.
• ECG; arterial gas if hypoxia.

Differential diagnosis. Decompression sickness (chokes), spontaneous pneumothorax, oesophageal rupture, pulmonary embolism, myocardial infarction, aortic dissection, pneumonia, asthma.

• 100% oxygen by non-rebreather mask at 15 litres/minute to speed gas resorption; keep patients with pneumomediastinum or small pneumothorax on high flow oxygen with observation.
• Tension pneumothorax: immediate needle decompression with a 14 gauge cannula into the 2nd intercostal space in the midclavicular line or the 4th to 5th intercostal space in the anterior axillary line, followed by chest drain.
• Symptomatic or large pneumothorax: chest drain by small bore tube. A chest drain is needed before any hyperbaric treatment or flight.
• Subcutaneous emphysema or mediastinal air alone: observation, oxygen and analgesia.
• Paracetamol 1 g orally every 6 hours as needed, maximum 4 g in 24 hours (3 g if under 50 kg, chronic alcohol excess or liver disease). Reduce dose in hepatic impairment; extend dosing interval when eGFR is under 30.
• Suspected gas embolism: give emergency treatment with positioning, 100% oxygen and urgent recompression.
• Pleurodesis or surgery for persistent air leak or recurrence.
• Return to diving: usually permanently unfit after pulmonary barotrauma with an unexplained or structural cause, and after pneumothorax unless a specialist confirms surgical pleurodesis and normal lung CT.

Monitoring. Repeat chest radiograph at 6 hours and at 24 to 48 hours; continuous oximetry; review of drain output.

Referral and escalation. Emergency transfer for any tension, embolic or severe presentation; cardiothoracic review for persistent leak; diving medicine physician for fitness assessment.