Background: Cold-water immersion is the gold standard for field treatment of an exertional heat stroke (EHS) casualty. Practical limitations may preclude this method and ice sheets (bed linens soaked in ice water) have emerged as a viable alternative. Laboratory studies suggest that this is an inferior method; however, the magnitude of hyperthermia is limited and may underestimate the cooling rate in EHS casualties.
Objective: Our aim was to determine the prehospital core cooling rate, need for continued cooling on arrival to the emergency department, and mortality rate associated with ice sheet use.
Methods: De-identified retrospective data were obtained from emergency medical services (EMS) and included presence or absence of altered mental status, cooling measures applied prior to EMS arrival, and time and core temperature (Tc; rectal) on-scene and on hospital arrival. Cooling rate was calculated from time and temperature data. Mortality data were obtained from the U.S. Army Combat Readiness Center.
Results: There were 462 casualties that met inclusion criteria. The cooling rate for the entire sample was 0.07°C ± 0.08°C · min-1. EHS casualties with an observed initial Tc < 39°C had an en route cooling rate of 0.03°C ± 0.04°C · min-1 vs. initial Tc ≥ 39°C cooling rate of 0.16°C ± 0.08°C · min-1. There was one fatality due to EHS, for a mortality rate of 0.20% (95% CI 0.01-1.20%).
Conclusions: The cooling rate in EHS casualties with initial Tc ≥ 39°C was approximately double that reported in laboratory studies. The observed mortality rate was comparable with casualties treated with cold-water immersion. Our data suggest that ice sheets provide a viable alternative when practical constraints preclude cold-water immersion.
Keywords: Cooling; Heat stroke; Hyperthermia; Military medicine.
Published by Elsevier Inc.