PULMONARY OVERINFLATION

This occurs in scuba divers breathing compressed air.
 On ascending from 10 m to the surface the lung volume doubles. Unless air is driven off by repeated exhalation, the alveoli become over-pressurised and rupture.This can happen in divers of no more than 2m.
Clinical features
Air from ruptured alveoli may escape in one of three ways and cause:

1. Interstitial emphysema in the chest, neck or retro peritoneal space with the production of pain, crepitus, impaired venous return and characteristic radiographic appearances;
2. Pneumothorax;
3. Air embolism where air leaks into the pulmonary capillaries, reaches the coronary or cerebral arteries, impairs local circulation, increase capillary permeability and precipitates intravascular coagulation.

The clinical condition is usually evident within minutes of surfacing, and varies from minor changes of mood to apnoea, coma and cardiac arrhythmia.
Management

Treatment requires recompression, but while transporting the patient supine to the treatment centre it is important to maintain a good airway, administer 100% oxygen, treat any dysrhythmia, treat hypotension with fluids and dopamine by i.v. infusion and control seizures with diazepam. Air embolism is one of the commonest causes of death among divers