Great difficulty is experienced in scuba divers asthma treatment when they are rescued and survive until recompression. They may suffer a difficult clinical complex comprising deep unconsciousness from near-drowning and probable cerebral gas embolism, respiratory impairment from near-drowning and asthma.
The problems of combining respiratory support and recompression therapy (restricted to 18 metres because of the requirement for 100 per cent oxygen in the presence of arterial hypoxia), the dangers from arrhythmias, and the possible arterialization of trapped pulmonary air emboli with sympathomimetic drugs, all make these cases a nightmare. Deeper recompression, even though the patient isnot responding, may well be a death sentence, and ultimate decompression is daunting with an arterial oxygen tension less than 50 mmHg! Some successes are doubtful achievements with residual hypoxic brain damage.
Occasional episodes of otherwise inexplicable and serious acute decompression illness have been observed. Even accepting that the case reports are incomplete (especially as regards previous medical history), it seems evident from the DAN data that the risk of arterial gas embolism and severe decompression sickness are significantly greater in current asthmatics, with an odds ratio of 4.16. The exact degree of increased risk is a matter of controversy.
Other risks have been observed, and unexplained unconsciousness at depth is one of these. There is no specific disadvantage in the use of inhaled steroids, taken in moderation, and the hope is that some of the new asthma treatment drugs now under development will totally block the hyperreactive and bronchoconstrictive effects of asthma (best diving). When this is achieved then the specific provoking factors associated with scuba diving may be blocked and, if no lung damage has occurred, the optimistic hopes of safe diving for asthmatics may be realized.
WS, a very fit dive instructor experienced two episodes of unconsciousness under similar conditions, about one year apart. They both were associated with diving between 30-50 metres depth, non-stressful and requiring little exertion. They both occurred 10 or more minutes after reaching the sea bed, and there were no problems during descent, and specifically no difficulty with middle-ear autoinflation.
Other divers on the same dives used similar scuba equipment and gases from the same compressor (WS's own dive shop) and experienced no difficulty.
The first episode resulted in a sensation of imminent loss of consciousness, to a severe degree and resulted in him ditching his weight belt and ascending, with help. With the ascent he regained his normal state of awareness. On his second episode he totally lost consciousness and was brought to the surface by one of the companion divers. He was fully conscious and alert within a few minutes of surfacing. Following this dive he was aware of a dull headache.
The only contributory factors that could be ascertained were as follows: He was renowned for consuming extremely small quantities of air and he did admit to employing 'skip breathing' in the earlier part of his diving career-although such a voluntary decision was not made over the recent years. He was also an asthmatic of moderate degree. He had not taken any anti-asthma medication prior to the dives. He then sold his diving practice, and refrained from diving activities.
Provisional diagnosis: a combined carbon dioxide/nitrogen narcosis effect asthma contribution.
Whatever the explanation, remember the maxim that any diving accident not explained and not prevented, will recur under similar conditions.