Tension pneumothorax in a ventilated patient

This is a tension pneumothorax. Air enters the pleural space with each breath and cannot leave. Pressure builds, the lung collapses, the mediastinum is pushed away, and venous return to the heart is blocked. The result is obstructive shock: hypotension, tachycardia, distended neck veins and profound hypoxia. Positive-pressure ventilation, especially after an increase in pressures, is a classic cause.

The diagnosis is clinical. Tracheal deviation is a late sign; absent breath sounds and hyper-resonance on one side with sudden cardiovascular collapse are enough. No imaging should be obtained before treatment, because the patient may arrest during the delay.

Immediate decompression is required. In an adult, a large-bore cannula is inserted in the fourth or fifth intercostal space in the anterior axillary line (the site now preferred over the second intercostal space mid-clavicular line, because chest wall thickness there often exceeds cannula length). A rush of air confirms the diagnosis. Alternatively, in a ventilated patient, a finger thoracostomy can be done directly. Decompression is a temporary measure and must be followed at once by a formal intercostal catheter (chest drain).

Therapeutic Guidelines and trauma teaching (EMST/ATLS) place this in the 'breathing' step of the primary survey, before circulation is addressed.

Vasopressors and fluid cannot overcome a mechanical obstruction to venous return. Continuing high-pressure ventilation without decompression drives more air into the pleural space and can cause cardiac arrest.