Cranial-neck and inhalation rewarming failed to improve recovery from mild hypothermia

INTRODUCTION: Rewarming from hypothermia in a field setting is a challenge due to the typical lack of significant power or heat source, making the targeted application of available heat critical. The highly vascular area of the head and neck may allow heat to be rapidly transferred to the core via blood circulation. At the same time, the warming of only a small skin surface may minimize the rapid rise in skin temperature proposed to attenuate shivering and endogenous heat production. Therefore, we investigated the efficacy of targeting the head and neck for rewarming from mild hypothermia. METHODS: There were 16 participants (9 men, 24.1 +/- 4.5 yr, 15.5 +/- 3.9% body fat; 6 women, 23.0 +/- 5.4 yr, 20.8 +/- 3.2% body fat) who were cooled in 15 degrees C water until rectal or esophageal temperature reached 35.5 degrees C, whereupon they were removed and provided passive (PASS), cranial-neck (CN), or cranial-neck and inhalation (CNIR) rewarming. Heart rate and skin temperature were also measured. RESULTS: The mean cooling times were PASS=83 min (range: 22-295 min), CN=94 min (range: 28-314 min), CNIR=97 min (range: 22-285 min). No significant differences (p > 0.05) were found for magnitude of after-drop (PASS = 0.33 +/- 0.24 degrees C, CN = 0.31 +/- 0.18 degrees C, CNIR = 0.29 +/- 0.28 degrees C esophageal temperature) and duration of afterdrop (PASS = 15.4 +/- 10.2 min, CN = 13.0 +/- 10.1 min, CNIR = 8.8 +/- 6.9 min). No significant differences (p > 0.05) were found for rewarming rate (PASS = 1.85 +/- 1.33 degrees C x h(-1), CN = 1.45 +/- 1.04 degrees C x h(-1), CNIR = 2.24 +/- 1.51degrees C x h(-1) esophageal temperature). DISCUSSION: In summary, neither cranial-neck nor cranial-neck and inhalation rewarming combined have an advantage in reducing the magnitude and duration of after-drop or increasing the rewarming rate over passive rewarming.