A Randomized Controlled Trial of a Novel Application of Chemical Cold Packs for Treatment of Exercise-Induced Hyperthermia

Background

Heat-induced illness is common around the world and is associated with significant morbidity and mortality. Despite having never been shown to be effective, a traditional cooling technique in the prehospital environment is applying chemical cold packs (CCPs) to skin covering the large vessels of the neck, groin, and axillae. An alternative placement of CCPs to the glabrous skin surfaces that contain densely packed subcutaneous vascular structures may be more efficacious.

Objective

The purpose of this study was to compare the cooling effect of CCPs applied to the neck, groin, and axillae versus glabrous skin of the cheeks, palms, and soles for exercise-induced hyperthermia.

Methods

In this prospective, randomized, crossover trial, 10 healthy adult male volunteers walked on a treadmill in a heated room (40°C ± 0.5°C, relative humidity 20% to 35%) wearing insulated military overgarments. Esophageal temperature (T_es) was monitored throughout the trials. The primary stop criterion for exercise was T_es = 39.2°C. The subjects then rested in the hot room for 30 minutes Each subject participated in 3 heat stress trials: a no treatment trial followed by 2 randomly ordered cooling trials, namely, traditional (neck, groin, and axillae) or glabrous (cheeks, palms, soles). Participant trials were separated by a minimum of 2 days.

Results

With no treatment, T_es decreased by 0.3 ± 0.2°C in the first 5 minutes, then stabilized for the ensuing 25 minutes. With traditional cooling, T_es decreased by 0.4 ± 0.2°C in the first 5 minutes, followed by a linear decline of 0.17°C over 10 minutes. Glabrous skin cooling enhanced the treatment effect: T_es decreased by 0.6 ± 0.2°C in the first 5 minutes and followed by a linear decline of 0.30°C over 10 minutes (P < .001).

Conclusions

Application of CCPs to glabrous skin was more effective for treating exercise-induced hyperthermia than was the traditional cooling paradigm. This novel cooling technique may be beneficial in reducing the morbidity and mortality of heat illness in the prehospital environment.