Friday, April 14, 2006

Dehydration and Diving - Does It Really Increase the Risk for DCS?

Dehydration is often listed as one of the main factors that are thought to increase the risk of decompression illness, it having been suggested that hydration may enhance inert gas removal or increase surface tension of the blood. There is usually a caveat stating that this has not been studied. Now, in the Journal "Aviation, Space and Environmental Medicine", Fahlman and Dromsky at the Naval Medical Research Center have studied pigs and have shown that yes, there is an increased risk for DCS due to dehydration.

In an article titled "Dehydration effects on the risk of severe decompression sickness in a swine model", they showed that dehydration significantly increased the overall risk of severe DCS and death. Specifically, it increased the risk of cardiopulmonary DCS, and showed a trend toward increased CNS DCS. In addition, dehydrated subjects manifested cardiopulmonary DCS sooner and showed a trend toward more rapid death (p < 0.1).

Here is a portion of the abstract of the article published in the February 2006 issue of Aviat Space Environ Med. (2006 Feb;77(2):102-6.)
BACKGROUND: Several physiological factors have been suspected of affecting the risk of decompression sickness (DCS), but few have been thoroughly studied during controlled conditions. Dehydration is a potential factor that could increase the risk of DCS. It has been suggested that hydration may enhance inert gas removal or increase surface tension of the blood.

HYPOTHESIS: Dehydration increases DCS risk.

METHODS: Littermate pairs of male Yorkshire swine (n=57, mean +/- 1 SD 20.6 +/- 1.7 kg) were randomized into two groups. The hydrated group received no medication and was allowed ad lib access to water during a simulated saturation dive. The dehydrated group received intravenous 2 mg x kg(-1) Lasix (a diuretic medication) without access to water throughout the dive. Animals were then compressed on air to 110 ft of seawater (fsw, 4.33 ATA) for 22 h and brought directly to the surface at a rate of 30 fsw x min(-1) (0.91 ATA x min(-1)). Outcomes of death and non-fatal central nervous system (CNS) or cardiopulmonary DCS were recorded.

RESULTS: In the hydrated group (n=31): DCS=10, cardiopulmonary DCS=9, CNS DCS=2, Death=4. In the dehydrated group (n=26): DCS=19, cardiopulmonary DCS=19, CNS DCS=6, Death=9.

CONCLUSION: Hydration status at the time of decompression significantly influences the incidence and time to onset of DCS in this model.

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