Reduction of Afterdrop by Using Active External Warming During Treatment of Accidental Hypothermia-A Randomized, Crossover Trial.

Abstract

This study investigates the impact of active external warming on afterdrop in simulated accidental hypothermia, compared to the effect of passive warming measures. This study used data from a randomized crossover field study of experimental hypothermia. Hypothermia was induced in 11 healthy volunteers by pharmacological inhibition of endogenous thermoregulation and exposure to -2°C ambient air in a glacial ice tunnel, wearing wet clothes for a maximum of 2 h, or until their esophageal temperature reached 35°C. Esophageal temperature was measured using a transnasal probe. After cooling, wet clothing was removed and the participants were placed in a hypothermia wrap system for 1 h, with three different sources of active warming applied to the participants in the intervention scenario. After 1 h, the participants were walked with minimal support for balance out of the ice tunnel to a warm tent to recover. The 10 min after the end of the rewarming phase was defined as the afterdrop phase. Most participants experienced a small drop in temperature during the wrapping phase between the cooling and rewarming phases, followed by a second larger afterdrop while walking out of the ice tunnel. The afterdrop was smaller in the actively rewarmed group, with a mean drop of 0.3°C (min 0.0°C, max 1.2°C) compared to 0.7°C (min 0.0°C, max 1.6°C) in the passively rewarmed group. Adding active external warming reduces afterdrop compared with using only passive external warming measures in non-shivering individuals. These results may increase understanding of both the afterdrop phenomenon and heat distribution in the body during rewarming. This study assessed temperature afterdrop in controlled hypothermia in healthy volunteers who were treated with active external rewarming or passive rewarming. These findings provide detailed insight into how temperature redistribution can occur during rewarming, at least in healthy cases.