Chemical Cold Packs May Provide Insufficient Enthalpy Change for Treatment of Hyperthermia

ObjectiveHeat illness is a common ailment that, if left untreated, is associated with high morbidity and mortality. Chemical cold packs (CCPs) and ice packs are widely used in the pre-hospital setting and by those with limited resources, yet no controlled studies have compared the cooling of ice to that of CCPs. This study determined the theoretical cooling of CCPs on a benchtop model, comparing the results to similarly sized ice packs, and is the first known comparison of these hyperthermia treatments.MethodsThe CCPs used in Stanford University's Emergency Department were activated in an insulated volume of water (2 L), and temperature was recorded at 1-second intervals in a controlled environment (41°C at 20% humidity). The procedure was repeated with 1-quart ice packs.ResultsThe CCPs resulted in a 5.25°C degree temperature drop, with a time constant (time to 63% of initial temperature—a common engineering characterization metric) of 1.72 minutes for the test volume. Ice packs resulted on average in a 19.8°C temperature change, with a time constant of 26.8 minutes. The CCPs provide less overall temperature change and were shorter lived. Application of 6 CCPs on a 50th percentile male (weight 86.6 kg, height 1.7 m), assuming ideal heat transfer, would result in less than 0.5°C temperature change. Similarly configured ice packs would result in a 2.5°C change.ConclusionsExperiments demonstrate that CCPs are inferior to similarly sized ice packs for thermal regulation, and lose their effectiveness more quickly. These findings support the consideration of ice packs as an alternative to chemical cold packs when cooling hyperthermic patients.