INHALATION REWARMING FROM HYPOTHERMIA - AN EVALUATION IN -20-DEGREES-C SIMULATED FIELD CONDITIONS

The present study evaluates the efficacy of inhaling warm moist air as a method of rewarming from hypothermia in -20 degrees C field conditi ons, The method of inhalation rewarming Is compared to two other metho ds of rewarming: a) passive rewarming; and b) passive rewarming, with a respiratory heat exchanger designed to minimize respiratory heat los s. Eight male subjects were rendered hypothermic by immersion in 15 de grees C water for 1 h. They were withdrawn from the tank earlier, in t he event that their rectal temperature (Tre) decreased to 35 degrees C , or by 1.5 degrees C from the pre-immersion value. Upon completion of the immersion, they were placed In a well-insulated sleeping bag asse mbly and transferred to a cold room maintained at -20 degrees C for a 2 h rewarming period. They participated in 3 trials: Control-passive r ewarming; Heat Treat(R)-inhalation rewarming with the Heat Treat(R); H ME-passive rewarming in conjunction with a respiratory heat and moistu re exchanger (HME). During the rewarming period, inspired air temperat ure was -19.4 +/- 1.1 degrees C in the control trial. In the HME and H eat Treat(R) trials subjects breathed via an oro-nasal mark. The inspi red air temperature was +20.5 +/- 1.2 degrees C in the HME and +36.2 /- 2.9 degrees C in the Heat Treat(R) trial, The post-immersion drop i n Tre was significant in all conditions. The reduction in the post-exp osure drop in Tre observed with the Heat Treat(R) may be attributed to the minimization of respiratory heat loss, since the magnitude of the reduction was similar to that observed with the HME. Neither the HME nor the Heat Treat(R) improved the rate of Tre rewarming of well-insul ated shivering subjects in a -20 degrees C ambience, Tre rewarming rat es observed with inhalation rewarming in laboratory studies may over-e stimate the rates of rewarming that would commonly be observed during rewarming in the field.