Prehospital Use of Forced Air Warming for Treatment of Accidental Hypothermia - A Pilot Study

Accidental hypothermia is defined as an involuntary drop in core body temperature below 35°C.

Hypothermia is a risk factor for cardiac arrythmia, pulmonary oedema, coagulopathy and neurological pathology. Isolated accidental hypothermia is potentially lethal on its own, and it is also an independent risk factor for increased mortality in patients with traumatic injury.

When core temperature drops, the body will automatically activate compensatory mechanisms in order to both increase thermic production and minimize heat loss in order to restore normal temperature. The mechanisms for thermal homeostasis are complex, strictly regulated and effective.

Until quite recently, active external rewarming was considered to be harmful and dangerous for patients with accidental hypothermia. A fear of fatal complications such as increased afterdrop and "rearming syndrome" leading to dangerous arrythmias and a drop in blood pressure which in a worstcase scenario could lead to circulatory collapse, shock and potentially death.

Given the potentially detrimental consequences of being cold, any advice to abstain from warming patients should be well-documented, and the adverse effects of warming should outweigh those of being hypothermic. The lack of evidence for this claim that active external rewarming is dangerous along with many reports of successful external rewarming is leading to a change in most guidelines where active external rewarming is now an advisable treatment option. A variety of different technological devices exist for the purpose of rewarming, but there is no established standard which is proven superior to others. Several trials have compared different rewarming methods, but evidence is limited. There is particularly deficient evidence regarding the amount of heat available for transfer from different methods and also the required amount of heat transfer for the rewarming to have a significant clinical impact. There is however reason to be cautious with active external rewarming of hypothermic patients. In a normothermic patient with normal circulatory function, thermal energy will be absorbed by the blood which flows back into central circulation distributing the heat evenly into a large volume. In a hypothermic patient there will be less cutaneous blood flow and less heat will be transferred to systemic circulation. This means that heat will accumulate on the skin surface and increase the risk of cutaneous injury, and there are several reported cases of this. Hypothermia research with volunteer research participants is a complicated matter for many reasons.