Efficacy of Head and Torso Rewarming Using a Human Model for Severe Hypothermia

Abstract

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).

Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update

“…Applying heat to the head, although requiring more technique to insulate and apply the heat, has been shown to be equally effective in shivering and nonshivering subjects, thus providing an alternative warming approach in extenuating circumstances. 69 Recommendations. Apply heat sources to the axillae, chest, and back.…”

Risk of Burns During Active External Rewarming for Accidental Hypothermia

“…Application of any portable heat source to the torso will not significantly increase peripheral blood flow and can be considered hemodynamically safe. 2 ,3,6,7 However, the 3 incidents reported here have emphasized a potential risk in that active external warming may cause first- to third-degree burns. Burn injuries may occur through misuse or unexpected consequences, 14,15 warranting careful attention to manufacturer instructions and vigilant monitoring.…”

“…One significant precipitating factor is anything that increases blood flow to the cold limbs (especially the legs); this can cause hypotension and further core cooling as blood cools in the periphery and returns to the heart (afterdrop) or return of harmful metabolites from the cold periphery. 2,3,6,7 Figure 3. First-degree burn of forearm in a cold adult subject who was warmed with a warm water perfused blanket on a forearm, which was placed in a prototype negative pressure warming device.…”

“…INCIDENT 3 In a more recent incident (2017), adult volunteer subjects were cooled in 8 C water to a T es of 36 C. They were then warmed by a charcoal heater (HEATPAC personal heater, Emergco, Vancouver, Canada) applied either to the head or chest, after shivering was pharmacologically suppressed with IV meperidine (maximum cumulative dose of 3.3 mg$kg -1 ). 6 The HEATPAC consists of an combustion chamber (24 Â 12 Â 6.5 cm) containing a charcoal briquette and a small fan that blows warm air from the chamber through 4 flexible, noncollapsible heating ducts (110 Â 2.5 Â 1 cm). Manufacturer instructions indicate the chamber should be inserted into the supplied insulated pouch, but the heating ducts can be applied directly to the skin.…”

Efficacy of warming systems in mountain rescue: an experimental manikin study

“…Meperidine was administered in some of these subjects in order to attenuate shivering, allowing one to calculate the mean value of M (W/m 2 ) for shivering and non-shivering subjects separately. We calculated an M value for a shivering victim (M shiv ) from 11 studies with a total of 77 participants (Giesbrecht et al 1994 ; Hultzer et al 2005 ; Grissom et al 2008 ; Pretorius et al 2008 ; Lundgren et al 2009 ; Thomassen et al 2011 ; Sran et al 2014 ; Kumar et al 2015 ; Henriksson et al 2015 ; Kulkarni et al 2019 ; Hurrie et al 2020 ). An M value for a non-shivering patient (M non-shiv ) (e.g., a patient treated with opioids) was calculated from six studies with a total of 37 subjects (Giesbrecht et al 2005 ; Hultzer et al 2005 ; Pretorius et al 2006 ; Lundgren et al 2009 ; Kulkarni et al 2019 ; Hurrie et al 2020 )—see Supplementary file .…”