Introduction-To evaluate the rewarming effectiveness of a similar amount of heat (from a charcoal heater) applied to either the head or torso in a human model for severe hypothermia in which shivering is pharmacologically inhibited in mildly hypothermic subjects. Methods-Six male subjects were cooled on 3 different occasions, each in 8˚C water for 60 min, or to a lowest core temperature of 35˚C. Shivering was inhibited by intravenous meperidine (1.5 mg¢kg ¡1), administered during the last 10 min of the cold-water immersion. Subjects then exited from the cold water, were dried, and were placed in a 3-season sleeping bag for 120 min in one of the following conditions: spontaneous rewarming only, charcoal heater on the head, or charcoal heater on the torso. Supplemental meperidine (to a maximum cumulative dose of 3.3 mg¢kg ¡1) was administered as required during rewarming to suppress shivering. Results-No significant differences were found in the postcooling afterdrop amount or core rewarming rates among the 3 conditions (0.8˚C¢h ¡1). During the last 30 min of rewarming the net heat gain was significantly higher in the head (85.8 §25.3 W) and torso (81.5 §6.3 W) conditions compared with the spontaneous condition (56.9 §12 W) (P<0.05). Conclusions-In our study, head and torso warming had the same core rewarming rates when shivering was pharmacologically inhibited in mildly hypothermic subjects. Therefore, in nonshivering cold subjects, head warming is a viable alternative if torso warming is contraindicated (eg, when performing cardiopulmonary resuscitation or working on open chest wounds).

Introduction We compared the effectiveness of 5 heated hypothermia wrap systems. Methods Physiologic and subjective responses were determined in 5 normothermic subjects (1 female) for 5 heated hypothermia wraps (with vapor barrier and chemical heat sources) during 60 min of exposure to a temperature of −22°C. The 5 systems were 1) user-assembled; 2) Doctor Down Rescue Wrap; 3) hypothermia prevention and management kit (HPMK); 4) MARSARS Hypothermia Stabilizer Bag; and 5) Wiggy's Victims Casualty Hypothermia Bag. Core and skin temperature, metabolic heat production, skin heat loss, and body net heat gain were determined. Subjective responses were also evaluated for whole body cold discomfort, overall shivering rating, overall temperature rating, and preferential ranking. Results The Doctor Down and user-assembled systems were generally more effective, with higher skin temperatures and lower metabolic heat production; they allowed less heat loss, resulting in higher net heat gain ( P<0.05). HPMK had the lowest skin temperature and highest shivering heat production and scored worse than the other 4 systems for the “whole body cold discomfort” and “overall temperature” ratings ( P<0.05). Conclusions The user-assembled and Doctor Down systems were most effective, and subjects were coldest with the HPMK system. However, it is likely that any of the tested systems would be viable options for wilderness responders, and the choice would depend on considerations of cost; volume, as it relates to available space; and weight, as it relates to ability to carry or transport the system to the patient.

ObjectiveThe purpose of the study was to determine, and compare, the effectiveness of five heated hypothermia enclosure systems (HES).MethodsThis study compared the thermal, physiologic and subjective responses of five subjects (one female) in five HES (with vapor barrier and chemical heat sources) during 60 min of exposure to a −22°C climate. The five systems were: 1) user-assembled (Control); 2) Doctor Down® Rescue Wrap® (DD); 3) Hypothermia Prevention and Management Kit (HPMK®); 4) MARSARS Hypothermia Stabilizer Bag (M); and 5) Wiggy’s Victims Casualty Hypothermia Bag (W). Core temperature, skin heat loss, and metabolic heat production were determined continuously. Subjective responses were also evaluated for: whole body cold discomfort; overall shivering rating; temperature rating; and overall preferential ranking.ResultsTotal heat loss was higher with HPMK, W and M compared to Control and DD (p<0.05). Net heat gain was higher with the Control and DD compared to W and M (p<0.05). Control, M and DD consistently scored better in the subjective scales.ConclusionsAlthough all systems provide insulation and heat, the Control (user-assembled), MASARS and Doctor Down systems were more effective, and preferred.FundingNSERC, Canada.

ObjectiveTo evaluate the rewarming effectiveness of the same amount of heat, using a charcoal heater, donated to the head or torso while using a human model for severe hypothermia where shivering is pharmacologically inhibited in mildly hypothermic subjects.MethodsSix male subjects were cooled on three different occasions each, in 8°C water, for 60 min or to a core temperature of 35°C. Shivering was inhibited by intravenous meperidine (1.5 mg/kg), administered during the last ten minutes of the cold-water immersion. Subjects then exited from the cold-water immersion and then were rewarmed for 120 min by one of the following: spontaneous rewarming only; charcoal heater on the head; or charcoal heater on the torso. Supplemental meperidine (maximum cumulative dose of 3.3 mg/kg) was administered as required during rewarming to suppress shivering.ResultsNo significant differences were found in the afterdrop amount or core rewarming rates among the three conditions. During the last 30 min of rewarming the net heat gain was significantly higher in the Head (85.8±25.3 W) and Torso (81.5±6.3 W) conditions compared to Spontaneous condition (56.9±12 W) (p<0.05).ConclusionsIn our study, Head and torso warming had the same core rewarming rates in a human model for severe hypothermia where shivering was pharmacologically inhibited in mildly hypothermic subjects. In non-shivering cold subjects, head warming is a viable alternative if torso warming is contraindicated.FundingNSERC, Canada.