Forced Air Speeds Rewarming in Accidental Hypothermia

doi:10.1016/S0196-0644(96)70237-8

Annals of Emergency Medicine

Volume 27, Issue 4, April 1996, Pages 479-484

Presented in part at the Eighth Annual Scientific Meeting of the Wilderness Medical Society, Keystone, Colorado, September 1992.

https://doi.org/10.1016/S0196-0644(96)70237-8 Get rights and content

Abstract

Study objective: To compare the rates of rewarming of forced-air and passive insulation as a treatment for accidental hypothermia. Methods: We carried out a prospective, randomized clinical trial in two urban, university-affiliated emergency departments. Our subjects were 16 adult hypothermia victims with core temperatures less than 32°C. A convective cover inflated with air at about 43°C (forced-air group) or cotton blankets (control group) were applied until the patient's core temperature reached 35°C. Members of both groups were given IV fluids warmed to 38°C and warmed, humidified oxygen at 40°C by inhalation. Results: The mean±SD initial temperature was 28.8°±2.5°C (range, 25.5°C to 31.9°C) in the patients who underwent forced-air rewarming and 29.8°±1.5°C (range, 28.2°C to 31.9°C) in those given blankets. Core temperature increased about 1°C/hour faster in patients treated with forced-air rewarming (about 2.4°C/hour) than in patients given only cotton blankets (about 1.4°C/hour, P=.01). Core-temperature afterdrop was detected in neither group. Conclusion: Forced air accelerated the rate of rewarming without producing apparent complications in hypothermic patients. [Steele MT, Nelson MJ, Sessler DI, Fraker L, Bunney B, Watson WA, Robinson WA: Forced air speeds rewarming in accidental hypothermia. Ann Emerg Med April 1996;27:479-484.]

Section snippets

INTRODUCTION

Hypothermia is defined as a core temperature less than 35°C. Core temperatures greater than 32°C, however, are rarely associated with morbidity unrelated to underlying pathology and are considered mild hypothermia. In contrast, lower temperatures are considered moderate to severe hypothermia because such temperatures can cause morbidity and mortality even in the absence of underlying pathology.¹ Moderate to severe hypothermia causes about 600 deaths each year in the United States.2, 3

Patients

MATERIALS AND METHODS

The study protocol was approved by the University of Missouri-Kansas City Adult Health Sciences Institutional Review Board and by the Cook County Hospital Scientific Committee. Because of the nature of the study, informed consent was waived.

Patients 18 years and older who presented to the emergency department of Truman Medical Center or Cook County Hospital between January 1, 1991, and April 1, 1993, with moderate to severe hypothermia were evaluated for study inclusion. Those who presented

RESULTS

Seventeen patients were initially enrolled in the study. However, one patient assigned to forced-air warming was withdrawn from the protocol when it was determined that he had panhypopituitarism. Among the remaining 16 study patients, 5 were enrolled at Cook County Hospital and 11 at Truman Medical Center. Two of the patients assigned to forced-air rewarming and one given blankets were intubated. One of the patients rewarmed with forced air did not receive warmed oxygen by mask because of

DISCUSSION

Core temperature during forced-air warming increased by about 1°C/hour faster than in patients warmed only with passive insulation. The difference is consistent with findings of previous studies that have quantified heat transfer during forced-air warming7, 8 and in subjects covered with one or three cotton blankets.¹⁵ Although we report results from only 16 patients, rewarming rates were similar in each group and the results were highly statistically significant. Such uniform results are

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Iatrogenic third-degree burn caused by off-label use of an infrared radiant heat lamp in a patient with accidental hypothermia
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Active external rewarming involves the direct exposure of the patient’s skin to an exogenous heat source, which has the potential for thermal injury [1]. Forced-air rewarming blankets (Bair Hugger™) have been shown to be effective for the treatment of accidental hypothermia without causing thermal injury [20–22] and for maintenance of core temperature during surgery [23]. Whole-body immersion in hot water, which causes massive vasodilatation and hypotension, is contraindicated as a rewarming method in hypothermic patients [24].
We report a case of third-degree burn involving 5% of the total body surface area caused by off-label use of Hanautherm®, an infrared radiant heat lamp for bed-warming, in a patient with severe accidental hypothermia. This iatrogenic burn required repeated surgical interventions and long-term hospitalization and caused subsequent cosmetic disfigurement and functional disability. To our knowledge, this is the first reported adult case of iatrogenic burn occurring during treatment for hypothermia. Radiant heat lamps should never be used for rewarming of patients with hypothermia without careful observation.
Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update
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To provide guidance to clinicians, the Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for the out-of-hospital evaluation and treatment of victims of accidental hypothermia. The guidelines present the main diagnostic and therapeutic modalities and provide recommendations for the management of hypothermic patients. The panel graded the recommendations based on the quality of supporting evidence and a balance between benefits and risks/burdens according to the criteria published by the American College of Chest Physicians. The guidelines also provide suggested general approaches to the evaluation and treatment of accidental hypothermia that incorporate specific recommendations. This is the 2019 update of the Wilderness Medical Society Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2014 Update.
The prehospital management of hypothermia — An up-to-date overview
2018, Injury
Accidental hypothermia concerns a body core temperature of less than 35 °C without a primary defect in the thermoregulatory system. It is a serious threat to prehospital patients and especially injured patients, since it can induce a vicious cycle of the synergistic effects of hypothermia, acidosis and coagulopathy; referred to as the trauma triad of death. To prevent or manage deterioration of a cold patient, treatment of hypothermia should ideally begin prehospital. Little effort has been made to integrate existent literature about prehospital temperature management. The aim of this study is to provide an up-to-date systematic overview of the currently available treatment modalities and their effectiveness for prehospital hypothermia management.
Databases PubMed, EMbase and MEDLINE were searched using the terms: “hypothermia”, “accidental hypothermia”, “Emergency Medical Services” and “prehospital”. Articles with publications dates up to October 2017 were included and selected by the authors based on relevance.
The literature search produced 903 articles, out of which 51 focused on passive insulation and/or active heating. The most effective insulation systems combined insulation with a vapor barrier. Active external rewarming interventions include chemical, electrical and charcoal-burning heat packs; chemical or electrical heated blankets; and forced air warming. Mildly hypothermic patients, with significant endogenous heat production from shivering, will likely be able to rewarm themselves with only insulation and a vapor barrier, although active warming will still provide comfort and an energy-saving benefit. For colder, non-shivering patients, the addition of active warming is indicated as a non-shivering patient will not rewarm spontaneously. All intravenous fluids must be reliably warmed before infusion.
Although it is now accepted that prehospital warming is safe and advantageous, especially for a non-shivering hypothermic patient, this review reveals that no insulation/heating combinations stand significantly above all the others. However, modern designs of hypothermia wraps have shown promise and battery-powered inline fluid warmers are practical devices to warm intravenous fluids prior to infusion. Future research in this field is necessary to assess the effectiveness expressed in patient outcomes.
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There were no significant differences in total heat transfer found between forced-air warming devices when only lower body blankets were used [61]. Forced-air systems surpass passive insulation and provide considerably more heat than circulating water [51,62,63]. Preoperative warming with forced air has been demonstrated to increase the heat content of peripheral tissues by more than what is normally lost through temperature redistribution during the hour following induction of anesthesia [64].
Since the initial design of surgical theatres, the thermal environment of the operating suite itself has been an area of concern and robust discussion. In the 1950s, correspondence in the British Medical Journal discussed the most suitable design for a surgeon's cap to prevent sweat from dripping onto the surgical field. These deliberations stimulated questions about the effects of sweat-provoking environments on the efficiency of the surgical team, not to mention the effects on the patient. Although these benefits translate to implant-based orthopedic surgery, they remain poorly understood and, at times, ignored.
A review and synthesis of the body of literature on the topic of maintenance of normothermia was performed.
Maintenance of normothermia in orthopedic surgery has been proven to have broad implications from bench top to bedside. Normothermia has been shown to impact everything from nitrogen loss and catabolism after hip fracture surgery to infection rates after elective arthroplasty.
Given both the physiologic impact this has on patients, as well as a change in the medicolegal environment around this topic, a general understanding of these concepts should be invaluable to all surgeons.
Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia
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^☆: From the Department of Emergency Medicine, Truman Medical Centerm Universitiy of Missouri–Kansas City School of Medicine, Kansas City, Missouri*;Thermoregulation Researach Laboratory, Department of Anesthesia, University of California, San Francisco, California^‡; and the Department of Emergency Medicine, University of Illinois at Chicago, Chicago, Illinois.^§

^☆☆: Supported by Augustine Medical, Incorporated, Eden Prairie, Minnesota; by National Institutes of Health grant GM49670; and by the Joseph Drown Foundation. The authors do not consult for, accept honoraria from, or own stock or stock options in any rewarming-related company.

^★: Address for reprints: Mark T Steele, MD, Department of Emergency Medicine, Truman Medical Center, 2301 Holmes, Kansas City, Missouri 64108, 816-556-3127, Fax 816-881-6282

^★★: Reprint no. 47/1/71693

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Forced Air Speeds Rewarming in Accidental Hypothermia☆,☆☆,★,★★

Abstract

Section snippets

INTRODUCTION

MATERIALS AND METHODS

RESULTS

DISCUSSION

Pharmacol Ther

Lancet

J Clin Anesth

J Clin Anesth

Ann Emerg Med

Resuscitation

Am J Emerg Med

Ann Emerg Med

Br J Anaesth

J Wilderness Med

Ann Fr Anesth Réanim

Ann Emerg Med

Accidental hypothermia: Review of the literature

Acta Anaesthesiol Scand

Hypothermia-associated death: United States, 1968-1980

JAMA

Hypothermia-related deaths: Cook County, Illinois, November 1992-March 1993

Morbid Mortal Wkly Rep

Hypothermia: Pathophysiology, clinical settings, and management

Ann Intern Med

Skin-surface warming: Heat flux and central temperature

Anesthesiology

Comparison of forced-air patient warming systems for perioperative use

Anesthesiology