A detailed investigation into the causes of recreational scuba diving deaths4,5 revealed that SWA was part of the sequence leading to death in 37 per cent of the cases – often a consequence of equipment problems or diving technique. In these cases, ‘leaking regulators’ were either observed and commented on by the victim beforehand or were demonstrated during the subsequent diving investigation.
The degree of aspiration increases with the volume of air required (e.g. with exertion, swimming against currents, panic) and/or with a diminished line pressure to the second stage.
SWA often formed a vicious circle with panic and exhaustion.
Hypoxia from SWA aggravated the problems of fatigue and exhaustion and was a precursor to loss of consciousness (with or without dyspnoea) in both near drowning and drowning cases.
In recreational scuba, the diver may attribute SWA-induced post-dive lethargic symptoms to sub-clinical decompression sickness or the unusual physical demands of the dive activity. If the diver is exposed to cold and develops the generalized symptoms characteristic of a feverish reaction, he or she will be unlikely to relate this to an unnoticed aspiration some hours earlier.
Whether the clinical manifestations are entirely caused by the hyper-osmotic sea water or whether there is a contribution to the pulmonary inflammatory response from the various organisms, vegetation and particulate matter in sea water is not known. Extrapolating from the animal experiments on aspiration, it would seem that the required inhaled volume of hyper-osmotic sea water would be more than 100 ml in humans. Small particle nebulization is not essential, but it is possibly relevant in those divers who were not aware of aspiration.
There is no distinct division in the initial presentations among SWAS, near drowning and drowning cases. Aspiration syndromes merge with near drowning – the intensity of the symptoms and the degree of consciousness often depending on environmental circumstances, the activity of the victim and the administration of oxygen.