Relationship between right-to-left shunts and cutaneous decompression illness

The presence of a large right-to-left shunt is associated with neurological decompression illness after non-provocative dives, as a result of paradoxi cal gas embolism. A small number of observations suggest that cutaneous dec ompression illness is also associated with a right-to-left shunt, although an embolic aetiology of a diffuse rash is more difficult to explain. We per formed a retrospective case-control comparison of the prevalence and sizes of right-to-left shunts determined by contrast echocardiography performed b lind to history in 60 divers and one caisson worker with a history of cutan eous decompression illness, and 123 historical control divers. We found tha t 47 (77.0%) of the 61 cases with cutaneous decompression illness had a shu nt, compared with 34 (27.6%) of 123 control divers (P < 0.001). The size of the shunts in the divers with cutaneous decompression illness was signific antly greater than in the controls. Thus 30 (49.2%) of the 61 cases with cu taneous decompression illness had a large shunt at rest, compared with six (4.9%) of the 123 controls (P < 0.001). During closure procedures in 17 div ers who had cutaneous decompression illness, the mean diameter of the foram en ovale was 10.9 mm. Cutaneous decompression illness occurred after dives that were provocative or deep in subjects without shunts, but after shallow er and non-provocative dives in those with shunts. The latter individuals a re at increased risk of neurological decompression illness. We conclude tha t cutaneous decompression illness has two pathophysiological mechanisms. It is usually associated with a large right-to-left shunt, when the mechanism is likely to be paradoxical gas embolism with peripheral amplification whe n bubble emboli invade tissues supersaturated with nitrogen. Cutaneous deco mpression illness can also occur in individuals without a shunt. In these s ubjects, the mechanism might be bubble emboli passing through an 'overloade d' lung filter or autochthonous bubble formation.