Hypobaric decompression sickness

The Royal Australian Air Force (RAAF) mimics emergency aircraft decompression and hypoxia in a chamber decompressed over two to six minutes to a simulated altitude of 25,000 feet (7500m). Air crews in the chamber are trained to use oxygen apparatus including positive pressure breathing systems under these conditions. Over a seven year period, the RAAF has performed approximately 2500 subject decompressions and the Alfred Hospital Hyperbaric Service has treated 11 patients suffering decompression sickness (DCS) following this hypobaric exposure. The 11 patients (eight males, three females, mean age 26±4 years) presented with typical DCS, with joint pains (9), paraesthesiae (7) and concentration and memory deficits (6). One had major neurological deficits including ataxia and dysarthria. Patients required a mean of seven treatments (range 2–25) to a depth of 18m on 100% oxygen. Two patients with refractory symptoms were recompressed with a 50: 50 mix of helium and oxygen and the patient with severe neurological deficit required recompression to 30m. Nine patients had complete resolution of DCS with treatment, one patient resolved fully by one month after treatment, the patient with more severe neurologic deficit recovered completely by 12 months and one patient with persistent mild sensory deficits was lost to follow‐up by the Alfred Hospital. There were no major differences in presenting symptoms, number of treatments, or outcome between these patients and 422 treated patients suffering DCS following diving over the same time period. DCS may occur with exposure to high altitude. The severity and treatment is similar to that occurring following diving. Resolution of symptoms and signs may be achieved by recompression therapy. 1995 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine