Hydration, Diving, and SIPE, the Killer

As divers, when it comes to medical issues, we may be guilty of focusing too much on a single issue when there are other issues at stake too. Take, for instance, being adequately hydrated to avoid DCS.

It's well known that a dehydrated diver is at much greater risk of getting DCS when diving within what is assumed to be the safe parameters of either dive tables or dive computers. A dehydrated diver who gets a bends hit may not have drunk enough water, or perhaps he had drunk too much alcohol the night before, which suppresses the production of an anti-diuretic hormone, causing him to urinate more and dehydrate himself. (Surely you know how beer seems to pass right through you. Well, it does, dehydrating you.)

So, what do we do? We drink a lot of water. Even more so when we arrive in a hot country, especially if we're packing a few extra pounds or getting long in tooth. But, for divers, that may put us at risk for another diving malady: SIPE - Swimming Induced Pulmonary Edema.

Professor Neal W. Pollock (Université Laval, Québec, QC, Canada) recently wrote to Diving and Hyperbaric Medicine, critiquing an earlier published human study of water intake, mentioning in his letter: "It is important to be mindful that while a state of dehydration can likely increase decompression stress, a state of hyperhydration can increase the risk of immersion pulmonary edema [IPE or SIPE], and extreme cases can lead to hyponatremia, both serious conditions. Divers need to be thoughtful in balancing many risks and should generally avoid extremes in any direction."

In other words, avoid drinking too little or too much water.

This was reflected in a September Undercurrent article (SIPE - Be Aware of the Symptoms), which had been prompted by an article regarding tourist snorkel deaths in Hawaii. "It is easy to understand that a newly arrived visitor to the islands (who may be overweight) may not be acclimatized to the tropical heat and might compensate by over-hydrating before going in the water - with disastrous results."

We asked Jim Chimiak, MD, DAN's Chief Medical Officer, about this, and he told us. "This is a very interesting topic that has considerable pathophysiologic implications that do not allow a simple overhydration recommendation . . . . Hydration status impacts every organ system, and there is a physiologic range to maintain for good health. For instance, too little negatively impacts performance and decompression stress; too much can result in electrolyte changes and edema (peripheral, cerebral, pulmonary, etc.). The healthier, fitter one is, the wider the range for adequate hydration status. (Conversely, hydration status may not be the most significant controlling factor for a diver presenting with decompression sickness or edema.)"

One expert, however, isn't so bullish on the risks of dehydration. Dr. Peter Wilmshurst, known for his work on PFOs and their relationship with DCS, and more recently, the study of SIPE in previously unexplained deaths of divers, believes "The evidence that dehydration increases the risk of decompression sickness is weak, and DCS rarely causes death."

However, when it comes to too much hydration, he told Undercurrent, "The evidence that over-hydration can precipitate immersion pulmonary edema [oedema] is strong, and immersion pulmonary edema is fairly often fatal. The aim should be for divers to be in a state of normal hydration."

So, be advised: be properly hydrated, not too much water, and not too little. And go light on the booze. If you don't, it will either dehydrate you or lead to hyperhydration when in the morning you drink a lot of water after the night before.

- John Bantin

PS: See also Undercurrent (January) IPE and Why It's Good to Feel the Need to Pee.