Relationship between oxygen concentration and temperature in an exothermic warming device

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Actively warming hypothermic patients or preventing hypothermia is critical in optimising outcomes in patients with traumatic injuries. Our aim was to investigate the effect of ambient oxygen concentration on the rate and change in temperature of the TechTrade Ready-Heat II exothermic (oxygen-activated) warming blanket, to evaluate safety and ascertain the risk of thermal injury.


A mannequin covered with an exothermic blanket was placed in a sealed oxygen tent. An ambulance blanket was placed between the TechTrade Ready-Heat II exothermic blanket and the mannequin. Two temperature probes were placed directly on the surface of the mannequin; one on the torso away from the heating packs and the other directly beneath the exothermic heating pack. The mannequin was exposed to increasing oxygen concentrations at 10% increments, starting at 21%. The experiment was conducted nine times, each time using a new blanket. Maximum temperature of the mannequin ‘skin’ and rate of rise were recorded from both temperature sensors.


In room air (21% oxygen), the mannequin surface reached 52°C after 60 min, matching manufacturer specifications. At 30% oxygen concentration, the temperature directly beneath the exothermic heating pack exceeded the 65°C threshold at which rapid thermal burns occur, reaching 72.5°C, with minimal change in overall torso temperature.


The supplemental use of oxygen in patients with traumatic injuries that increases ambient oxygen levels in the presence of exothermic warming devices may represent a significant risk to the patient. We suggest that prehospital care providers remain highly vigilant of heat when using high-flow oxygen and the subsequent fire risk, while manufacturers of exothermic blankets should consider ways to improve safety.

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