Polar Life Pod Cooling Efficacy When Small Volumes of Water are Available to Treat Exercise-Induced Hyperthermia

IntroductionCold-water immersion is the standard of care for treating exertional heatstroke (EHS). The Polar Life Pod (PLP; Polar Products Inc, Stow, OH), a body-bag-like device, is a novel, portable cold-water immersion device with excellent cooling rates (>0.18°C·min^-1) when 151 to 208 L of water are used to treat hyperthermia. Unfortunately, these water volumes are not always available to treat EHS (eg, wilderness firefighting). Little research has examined whether the PLP with small water volumes meets expert recommendations for acceptable (ie, 0.08-0.15°C·min^-1) or ideal cooling rates (ie, >0.16°C·min^-1).MethodsThirty-two subjects (20 males and 12 females aged 21±2 y with a mass of 72.2±11.0 kg and a height of 170.4±7.2 cm) were assigned to 1 of 4 groups in this matched-pairs laboratory study. Participants wore a uniform and 9.5-kg rucksack and marched in the heat (wet-bulb globe temperature=26.1±0.1°C) until their rectal temperature (<i>T</i>_REC) was 39.5°C. Then they removed the uniform and sat in the heat (0 L) or lay in a PLP filled with 19, 38, or 76 L of ∼8°C water until <i>T</i>_REC was 38°C.ResultsBy design, all groups had comparable physical characteristics: body fat percentage (<i>P</i>=0.39), lean body mass (<i>P</i>=0.86), fat mass (<i>P</i>=0.13), body surface area (<i>P</i>=0.36), body surface area-lean body mass ratio (<i>P</i>=0.98), and body mass index (<i>P</i>=0.63). Subjects exercised for similar durations (<i>P</i>=0.66), and pre-immersion water temperatures were consistent between groups (<i>P</i>>0.05). <i>T</i>_REC cooling rates differed (0 L=0.03±0.01°C·min^-1, 19 L=0.13±0.08°C·min^-1, 38 L=0.10±0.03°C·min^-1, and 76 L=0.17±0.09°C·min^-1; <i>P</i>=0.002). No cooling-rate differences occurred between 19, 38, and 76 L (<i>P</i><0.05).ConclusionPLP with 76 L met expert recommendations for ideal cooling rates; 19 and 38 L demonstrated acceptable cooling rates. PLP may help save lives from EHS when water access is limited.