Polar Life Pod Cooling versus Ice Sheet Cooling following Simulated Military Conditioning Exercise.

Context: Exertional heatstroke (EHS) is a leading cause of death in athletes and the warfighter. Polar Life Pod (PLP) and ice sheet cooling (ISC) are two of the more portable cooling techniques to treat EHS and show promise for treating patients when large volumes of water or immersion devices (e.g., tubs) are not available. "Ideal" cooling rates consistent with excellent EHS prognoses exceed 0.16°C/min while "acceptable" rates are between >0.08°C/min and 0.15°C/min. No research has compared the cooling effectiveness of the Polar Life Pod (PLP), a body bag-like device, to ISC following simulated military conditioning exercise.

Objective: Determine if PLP or ISC reduced rectal temperature (TREC) differently and at 'acceptable' or 'ideal' cooling rates.

Design: Randomized, counterbalanced, crossover study.

Setting: Laboratory.

Patients or other participants: Fourteen participants (10 men, 4 women; age: 22±3y; mass:73.8±17.8kg; ht:168.5±7.8cm).

Interventions: Participants donned a military uniform and rucksack and marched in the heat (temperature=∼37.5°C; relative humidity=∼40%) until TREC was 39.5°C. Then they undressed and were wrapped in bed sheets presoaked in ice water (≤0.89±0.33°C) or lay in PLP filled with water (151.4±3.8L; 4.22±0.95°C) until TREC was 38°C.

Main outcome measures: TREC and cooling durations; calculated TREC cooling rates.

Results: Participants exercised in similar clothing, environmental conditions, and durations (PLP=50.5±9.9min, ISC=48.9±10.9min, P=0.38). PLP cooling rates differed from ISC and were 'ideal' whilst ISC rates were 'acceptable' (PLP=0.22±0.08°C/min; ISC=0.11±0.05°C/min, P<0.001).

Conclusions: PLP lowered TREC twice as quickly as ISC and at rates consistent with favorable EHS outcomes. PLP's faster cooling rates were likely due to it utilizing conductive and convective cooling, treating a larger body surface area, and providing a larger heat sink than ISC. PLP and ISC can be utilized to treat EHS, but PLP is preferred because it reduced TREC faster, utilized less ice, and required the same number of personnel and coolers as ISC.