Dehydration effects on the risk of severe decompression sickness in a swine model.
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.


OBJECTIVE
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. 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).


CONCLUSIONS
Hydration status at the time of decompression significantly influences the incidence and time to onset of DCS in this model.
Naval Medical Research Center, Diving Medicine, 503 Robert Grant Ave., Silver Spring, MD 20910-7500, USA.
Andreas
A
Fahlman
David M
DM
Dromsky
D000704:Analysis of Variance; D000818:Animals; D003665:Decompression Sickness / Q000209:etiology / Q000503:physiopathology*; D003681:Dehydration / Q000503:physiopathology*; D004198:Disease Susceptibility / Q000503:physiopathology*; D004242:Diving / Q000009:adverse effects*; D016015:Logistic Models; D008297:Male; D011897:Random Allocation; D012306:Risk; D018709:Statistics, Nonparametric; D016019:Survival Analysis; D013552:Swine