Diving equipment is designed to deliver compressed gas to the diver at the same pressure as the surrounding environment (e.g., at 33 fsw the diver breathes gas at a pressure of 2 ATA). Consequently, the compressed gas will expand during ascent according to Boyle's law, and the diver must allow the expanding gas to escape from the lungs, or it will rupture and dissect into the surrounding tissue. The resultant injury will depend on the location and amount of escaped gas. Symptoms of PBT sustained during ascent can appear immediately on surfacing or develop later.
Mediastinal and subcutaneous emphysema are the most common forms of the POPS. The patient usually presents with gradually increasing hoarseness, neck fullness, and substernal chest pain several hours after diving. Dyspnea, dysphagia, syncope, and other symptoms may be present as well. The history is usually diagnostic, although radiographs are indicated to verify the location of gas and exclude the presence of a pneumothorax.
The development of a pneumothorax as a result of PBT is uncommon but especially serious, for intrapleural gas cannot be released to the environment and is likely to progress to tension pneumothorax during ascent, leading to syncope, shock, or unconsciousness on surfacing.
Except for pneumothorax, which may require needle aspiration or tube thoracostomy, treatment of uncomplicated POPS typically requires only observation, rest, and, sometimes, supplemental oxygen. Recompression is necessary only in extremely severe cases.
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