Elsevier

Injury

Volume 35, Issue 1, January 2004, Pages 7-15
Injury

REVIEW
Hypothermia in the trauma patient

https://doi.org/10.1016/S0020-1383(03)00309-7Get rights and content

Abstract

Hypothermia is a common finding in severely injured patients. Historically described as a consequence of wartime casualties where cold exposure was common, this topic has resurfaced in the trauma literature because of the increasing recognition of the morbidity and mortality associated with hypothermia. Hypothermia, along with acidosis and coagulopathy, has been identified as a component of the “lethal triad” in injured patients, and has been shown to contribute to increased mortality in these patients. Decreases in core temperature during the course of initial evaluation and resuscitation are common, and can contribute to poor outcomes in the injured patient. As induced hypothermia has been shown to be beneficial in some clinical situations, recent animal studies have attempted to investigate whether hypothermia in the trauma patient has any beneficial effects. This review examines the incidence and pathophysiology of hypothermia, and discusses mechanisms of heat loss and rewarming techniques that can be utilized in the trauma patient.

Introduction

Hypothermia in humans is defined as a core temperature below 35 °C,4., 37. and has traditionally been classified into zones of severity based on the physiologic changes that occur with decreasing body temperature.12 Mild hypothermia, with core temperatures between 32–35 °C, is usually well tolerated, with compensatory cardiovascular changes designed to maintain temperature homeostasis. Below 32 °C, however, cardiac conduction disturbances become apparent, and at 28 °C serious dysrhythmias can occur. Below 28 °C heat production mechanisms begin to fail, and at 20 °C virtually all patients are asystolic.

These original definitions were introduced to describe hypothermia resulting from environmental exposures. In a multicenter study of over 400 cases of hypothermia due to exposure, core temperature less than 32 °C was associated with 21% mortality.6 In trauma patients, however, the presence of hypothermia was associated with a much higher mortality than patients who had suffered exposure. Jurkovich found that in 71 adult trauma victims, core temperature less than 32 °C was associated with 100% mortality, independent of the presence of shock, injury severity score, or volume of fluid resuscitation.30 Because the prognosis associated with hypothermia in the trauma victim is so poor, a separate classification of hypothermia has been developed for use in the injured patient (Table 1). As such, hypothermia in the trauma patient is classified as mild (36–34 °C), moderate (34–32 °C), or severe (below 32 °C).15

Section snippets

Physiologic effects of hypothermia

Regulation of body temperature occurs in the hypothalamus, which receives input from thermoreceptors along the distribution of the internal carotid artery, the posterior hypothalamus, and peripheral skin receptors.35 Homeothermic responses to cold include increased muscle tone and shivering, as well as metabolic increases from release of catecholamines and thyroxine.

Hypothermia can have marked physiologic effects on the cardiac, pulmonary, neurologic, and haemostatic systems (Table 2). In

Causes of hypothermia in the trauma patient

From the time of injury, trauma itself alters the normal central thermoregulation and blocks the shivering response. The thermoneutral zone is defined as the ambient temperature at which basal thermogenesis offsets continuing heat losses, and in humans, occurs at 28 °C.12 Maintaining euthermia when ambient temperatures are below the thermoneutral zone requires increased heat production and oxygen consumption. When tissue oxygen consumption is limited by shock, insufficient heat production occurs

Management of hypothermia

The first step in correcting hypothermia is the determination of core temperature. Unfortunately, studies have indicated that temperature is not often measured in the trauma patient, especially those who are severely injured.44 While oral and rectal temperatures are most commonly employed in the emergent setting, oesophageal and bladder temperatures have been shown to correlate more closely with core temperatures.35 A more recent development is the use of infrared tympanic membrane thermometry,

Hypothermia in the operating room

Hypothermia in the injured patient has marked clinical implications. Trauma patients with a core temperature of less than 32 °C were noted to have 100% mortality,30 compared to a 23% mortality for patients with the same temperature from exposure related hypothermia.6 Although many of these deaths are attributed to underlying conditions or associated diseases, several studies have demonstrated a significantly higher mortality among trauma victims with hypothermia. These studies have shown that

Ongoing research and controversies

Despite the physiologic changes induced by hypothermia and the potential for complications in the trauma patient, hypothermia has been noted historically to improve outcomes in certain clinical situations. Induced hypothermia is routinely employed during organ transplantation, cardiac surgery, and neurologic surgery, as it limits tissue ischaemia by decreasing overall metabolic activity and cellular oxygen consumption. As such, some authors have proposed that hypothermia may provide a

Summary

Hypothermia is a common finding in the trauma patient, and contributes to increased morbidity and mortality in this group of critically ill patients. Although initial temperatures may be normal, decreases in core temperatures during the course of initial evaluation and resuscitation are common. Hypothermia contributes to alterations in physiologic functions, and through alterations of the normal coagulation function, can contribute to further haemorrhage and shock in the injured patient. Both

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