Original Article
Effectiveness of Resistive Heating Compared With Passive Warming in Treating Hypothermia Associated With Minor Trauma: A Randomized Trial

https://doi.org/10.4065/76.4.369Get rights and content

Objectives

To determine the occurrence of hypothermia in patients with minor trauma, to test the hypotheses that resistive heating during transport is effective treatment for hypothermia and that this treatment reduces patients' thermal discomfort, pain, and fear, and to evaluate the accuracy of oral temperatures obtained at the scene of injury.

Patients and Methods

In December 1999 and January 2000, 100 patients with minor trauma were randomly assigned to passive warming or resistive heating. All patients were covered with a carbon-fiber resistive warming blanket and a wool blanket, but the warming blanket was activated only in those assigned to resistive heating. Core (tympanic membrane) and oral temperatures, heart rate, pain, fear, and overall satisfaction of patients were compared between the 2 groups on arrival at a hospital.

Results

Hypothermia was noted in 80 patients at the time of rescue. Mean initial core temperatures were 35.4°C (95% confidence interval [CI], 35.2°C-35.6°C) in the patients who received passive warming and 35.3°C (95% CI, 35.1°C-35.5°C) in those who received resistive heating. From the time of rescue until arrival at the hospital, mean core temperature decreased 0.4°C/h (95% CI, 0.3°C/h-0.5°C/h) with passive warming, whereas it increased 0.8°C/h (95% CI, 0.7°C/h-0.9°C/h) with resistive heating. Oral and tympanic membrane temperatures were similar. Mean heart rate decreased 23 beats/min in those assigned to resistive heating but remained unchanged in those assigned to passive warming. Patients in the resistive heating group felt warmer, had less pain and anxiety, and overall were more satisfied with their care.

Conclusions

Oral temperatures are sufficiently accurate for field use. Hypothermia is common even in persons with minor trauma. Resistive heating during transport augments thermal comfort, increases core temperature, reduces pain and anxiety, and improves overall patient satisfaction.

Section snippets

PATIENTS AND METHODS

This study was conducted with approval from the Ethics Committee of the Research Institute of the Vienna Red Cross. It was conducted in December 1999 and January 2000 in Vienna, Austria. Written consent was waived, but a verbal consent was obtained from the participants. Based on a preliminary study of 55 patients, we calculated that a sample size of 100 would provide more than a 99% chance of identifying a statistically significant difference in core temperature at an a level of 0.01. Thus, we

RESULTS

An audit confirmed that patients were properly assigned to passive warming or resistive heating. None of the enrolled patients dropped out of the study, and all patients completed the study in the group to which they were assigned. Thus, our analysis is based on 50 patients in each treatment group.

Although all injuries were minor, many of the patients were unable to telephone for help because they were intoxicated or because fractures restricted their movement. Time before rescue averaged 1 to

DISCUSSION

Our study patients had minor trauma. Nonetheless, initial core temperatures were almost 35.5°C, which is below the normothermic temperature range of 36.5°C to 37.5°C. Contributing factors included advanced age, alcohol intoxication, and prolonged time between injury and rescue. These data suggest that minor injuries are often associated with hypothermia.

Detection of hypothermia before a patient arrives at the hospital requires a method of temperature measurement suitable for routine field use.

CONCLUSION

Hypothermia is common, even in persons with minor trauma. Resistive heating during hospital transport augments thermal comfort, increases core temperature, reduces pain and anxiety, and improves overall patient satisfaction. Therefore, we recommend that persons with minor trauma be actively warmed during transport to the hospital.

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    • Cited by (0)

    Supported by ThermaMed, GmbH (Bad Oeynhausen, Germany), National Institutes of Health grant GM58273 (Bethesda, Md), the Research Institute of the Vienna Red Cross, the Commonwealth of Kentucky Research Challenge Trust Fund, and the Joseph Drown Foundation (Los Angeles, Calif). Mallinckrodt Anesthesiology Products, Inc (St Louis, Mo) donated the thermocouples.

    Dr Sessler is a paid consultant for ThermaMed, GmbH.

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    Copyright © 2001 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.