Effect of active external rewarming on esophageal temperature in simulated prehospital accidental hypothermia: a randomized crossover trial.

BACKGROUND

Prehospital rewarming is crucial to reduce mortality and improve outcomes in patients with accidental hypothermia. Although international guidelines recommend combining active external rewarming with passive rewarming, the effect of active external rewarming remains unclear. We evaluated the effects of active external rewarming compared to passive rewarming in cold-stressed, nonshivering volunteers.

METHODS

This randomized, crossover field study aimed to recruit 12 participants and was performed in May/June 2024 in Lom, Norway. The participants were dressed in wet clothing and placed in a - 2 °C ice tunnel for 2 h or until their esophageal temperature reached 35 °C. Endogenous thermoregulation, most importantly shivering, was suppressed using a drug protocol. After cooling, their wet clothes were removed, and they were rewarmed using either a combination of three different sources of active rewarming combined with passive rewarming (intervention) or passive rewarming only (control) while lying supine on a sleeping pad. The rewarming phase lasted for one hour. The primary outcome was the mean change in esophageal temperature analyzed using analysis of covariance. Secondary outcomes included mean skin temperature rewarming rates and subjective comfort scores.

RESULTS

Eleven participants completed the trial twice in a crossover fashion. The active rewarming group showed a mean increase in the esophageal temperature of 0.15 °C (- 0.16 °C to 0.45 °C), whereas the passive rewarming group experienced a mean decrease of - 0.05 °C (- 0.33 °C to 0.23 °C), indicating a difference in rewarming rate between the active and passive rewarming groups of 0.2 °C/h (-0.03 °C to 0.42 °C). Skin temperature rewarming rate was 1.5 °C/h higher in the active rewarming group than in the control group, although the difference was not statistically significant. The subjective comfort scores favored active rewarming.

CONCLUSION

The results from a simulated prehospital setting indicate that active warming may increase rewarming rates in accidental hypothermia treatment. Importantly, active warming may contribute to avoid a further drop in temperature during initial phases of treatment in cold environments.

TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT06342726. Registered 26.03.2024.