A Hidden Killer in Our Midst

How often has it been reported that a diver drowned while there was still plenty of air in his tank? For example, in 2015, a well-known professional underwater cameraman suffered breathlessness during a routine dive, something he had never experienced. He felt that his regulator no longer delivered sufficient air and found himself sucking hard on it -- but there was nothing wrong with it. In fact, he was on his way to what might have been considered just another mysterious drowning incident.

Luckily, he left the water unscathed, with nothing more than a severe scare, and after a thorough medical check-up, continued to dive. While he told us the story, he asked that we not reveal his name because he doesn't want it to impinge on his ability to attract work.

Peter Wilmshurst, a leading British cardiologist whose work in the 1980s demonstrated the correlation between PFO (patent foramen ovule) in the heart and decompression sickness, has recently been studying another hidden killer, which may have been responsible for mysterious drowning deaths of many competent divers worldwide.

Immersion pulmonary edema (IPE) is a life-threatening condition that affects surface swimmers, snorkelers, and divers. The precise incidence is unknown, because fatal cases can be, and probably have been in the past, mistaken for drowning. In both IPE and drowning, the lungs are waterlogged and heavy, so post-mortem findings can be similar.

IPE Can Cause Cardiac Arrest

In IPE, the lung alveoli fill with edema fluid. Immersion causes increased hydrostatic pressure, which immediately causes redistribution of blood from the periphery to the chest.

As the condition worsens, hypoxia increases, and unconsciousness can occur. This is exacerbated by a reduced partial pressure as a diver ascends, and can cause cardiac arrest.

Divers at risk have pre-existing cardiac disease and hypertension. Diving in cold water, encountering stress while diving -- heavy exertion in battling a current or waves -- and even breathing from an inefficient regulator can increase the risk of IPE. Even drinking a lot of liquid before diving (something many of us do as a precaution against the onset of DCS) can increase the risk.

The increase in water pressure at depth causes redistribution of blood from the periphery of the body to the chest, increasing heart filling pressure and stroke volume, and reduces total lung capacity. This happens with everyone, with fluid passing from the capillaries in the lungs to the lung tissue. The body counteracts this by excreting water through the kidneys -- that's why you have to pee during a dive -- but, over a period underwater, lung water increases. In some people, this rate of accumulation is greater than others.

Immersion in cold water increases the risk of IPE because blood vessels in arms and legs become narrower. Heavy exertion or poor air delivery of air does the same.

"An important indication that a diver had IPE is that they believed that their equipment was not working properly, even though later tests confirmed that the equipment was fine. If a diver is seen unnecessarily switching between their demand valves or using a buddy's secondary air supply, or if a diver with a re-breather is [seen repeatedly] purging the system, [it] may indicate the onset of IPE."

When a snorkeler or diver is breathless, observers must get that person out of the water. An individual who has suffered suspected IPE is at risk of further episodes and should consult a physician.

Besides a physical examination, it is usually necessary to assess cardiac function and test for myocardial ischemia, which might include such tests as an echocardiogram and a myocardial perfusion scan (or locally available alternatives).

(Abridged from UK Diving Medical Council report www.ukdmc.org)

And it doesn't only happen in cold water. This year a group of physicians based in Singapore described in a paper presented to the Undersea & Hyperbaric Medical Society a case of Swimming-Induced Pulmonary Edema (SIPE) suffered by a 21-year-old diver trainee after performing a swim of 2km (more than a mile) in water temperatures around 86°F (30°C). The conclusion was that development of SIPE in tropical waters suggests that other risk factors may be predominant. There should be a high index of suspicion when any strenuous in-water activity is conducted so that timely treatment may be instituted.

(Source: Kwek WMJ, Seah M, Chow W - UHMS 2017, Vol. 44, No. 3)