Cold-water immersion and the treatment of hyperthermia: Using 38.6°C as a safe rectal temperature cooling limit

Abstract

Context: Cold-water immersion is recommended for the immediate field treatment of exertional heat stroke. However, concerns exist over potential overcooling of hyperthermic individuals during cold-water immersion. Objective: To evaluate the recommendation that removing previously hyperthermic individuals from a cold-water bath at a rectal temperature (Tre) of 38.6°C would attenuate overcooling. Design: Controlled laboratory study. Setting: University research laboratory. Patients or Other Participants: Participants included 6 men and 4 women (age = 22 ± 3 years, height = 172 ± 10 cm, mass = 67.8 ± 10.7 kg, body fat percentage = 17.1% ± 4.5%, maximum oxygen consumption = 59.3 ± 8.7 mL̇kg2 -1̇min-1). Intervention(s): After exercising at an ambient temperature of 40.0°C for 38.5 ± 9.4 minutes, until T re reached 39.5°C, participants were immersed in a 2.0°C circulated water bath until Tre decreased to either 37.5±C or 38.6°C. Subsequently, participants were removed from the water bath and recovered for 20 minutes at an ambient temperature of 25°C. Main Outcome Measure(s): Rectal and esophageal temperatures were measured continuously during the immersion and recovery periods. Results: Because of the experimental design, the overall time of immersion was greater during the 37.5°C trial (16.6 ± 5.7 minutes) than the 38.6°C trial (8.8 ± 2.6 minutes) (t9 = 24.740, P = .001). During the recovery period after cold-water immersion, both rectal (F1,9 = 50.540, P < .001) and esophageal (F1,6 = 20.365, P = .007) temperatures remained greater in the 38.6°C trial than in the 37.5°C trial. This was evidenced by low points of 36.47°C ± 0.70°C and 37.19°C ± 0.716C for rectal temperature (t9 = 2.975, P = .016) and of 35.67°C 6 1.27°C and 36.72°C ± 0.95°C for esophageal temperature (t6 = 3.963, P = .007) during the recovery period of the 37.5°C and 38.6°C trials, respectively. Conclusions: Immersion for approximately 9 minutes to a rectal temperature cooling limit of 38.6°C negated any risk associated with overcooling hyperthermic individuals when they were immersed in 2°C water. © by the National Athletic Trainers' Association, Inc.