Recommended water immersion duration for the field treatment of exertional heat stroke when rectal temperature is unavailable

Abstract

Introduction: The recommended treatment for exertional heat stroke is immediate, whole-body immersion in < 10 °C water until rectal temperature (T_re) reaches ≤ 38.6 °C. However, real-time T_re assessment is not always feasible or available in field settings or emergency situations. We defined and validated immersion durations for water temperatures of 2-26 °C for treating exertional heat stroke.

Methods: We compiled data for 54 men and 18 women from 7 previous laboratory studies and derived immersion durations for reaching 38.6 °C T_re. The resulting immersion durations were validated against the durations of cold-water immersion used to treat 162 (98 men; 64 women) exertional heat stroke cases at the Falmouth Road Race between 1984 and 2011.

Results: Age, height, weight, body surface area, body fat, fat mass, lean body mass, and peak oxygen uptake were weakly associated with the cooling time to a safe T_re of 38.6 °C during immersions to 2-26 °C water (R² range: 0.00-0.16). Using a specificity criterion of 0.9, receiver operating characteristics curve analysis showed that exertional heat stroke patients must be immersed for 11-12 min when water temperature is ≤ 9 °C, and for 18-19 min when water temperature is 10-26 °C (Cohen's Kappa: 0.32-0.75, p < 0.001; diagnostic odds ratio: 8.63-103.27).

Conclusion: The reported immersion durations are effective for > 90% of exertional heat stroke patients with pre-immersion T_re of 39.5-42.8 °C. When available, real-time T_re monitoring is the standard of care to accurately diagnose and treat exertional heat stroke, avoiding adverse health outcomes associated with under- or over-cooling, and for implementing cool-first transport second exertional heat stroke policies.

Keywords: Cooling; Core temperature; Emergency response; Exercise; Heat illness; Heat stress; Hyperthermia.