ASSESSING THE RESPONSE OF HYPERTHERMIC MEN AND WOMEN TO THE CURRENT COLD-WATER IMMERSION GUIDELINES FOR EXERTIONAL HEAT STROKE TREATMENT

Abstract

INTRODUCTION According to best-practice guidelines, whole-body cold-water immersion is the most effective treatment for exertional heat stroke. How women respond to this treatment has received limited consideration despite some evidence suggesting women may cool more rapidly than men. This research evaluated the suitability of the existing exertional heat stroke guidelines for women. METHODS Endurance trained men (n=20, VO2max: 52.5±7.3 ml/kg/min, Body surface area (BSA): 1.63±0.77, Body fat %: 14.3±6.8, Lean mass %: 81.4±6.7) and women (n=18, VO2max: 46.7±5.3 ml/kg/min, BSA: 1.68±0.13, Body fat %: 26.1±6.3, Lean mass %: 69.6±6.1) ran in the heat (40°C, RH 20-40%) until their rectal temperature reached 39.5°C or above. Individuals were then immersed to the clavicle in a 2°C circulated water bath until rectal temperature lowered to 38.6°C. Rectal temperature was assessed throughout. Linear regression models were used to analyse immersion time. RESULTS Immersion time was not statistically different between men and women (mean difference [95% CI] = 68.4 sec [-48.9, 185.6]; p = 0.24) after adjusting for rectal temperature on immersion. The 90% confidence interval on the mean difference spanned from -30 sec to positive 2 min 45 sec, meaning that relatively large effects, favouring a longer immersion time for males, could not be ruled out, and therefore, the results are inconclusive. A model containing sex, immersion rectal temperature, and BSA explained the highest proportion of variance in immersion time (38%) compared to when lean mass (32%) or fat mass (34%) were included instead of BSA. CONCLUSION There was weak evidence that hyperthermic females cooled more rapidly than hyperthermic males during cold-water immersion (2°C); thus with further enquiry, females may require a shorter immersion time than males to reach the safety cooling limit. Future studies are needed to investigate the effect of BSA, lean and fat mass on cooling rate in heat stroke cases.