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Key Points

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  • Intoxication with either alcohol or drugs is very common in patients with hypothermia.

  • Most emergency thermometers cannot accurately read body temperatures below 34.4°C (94°F).

  • Many hypothermic patients have serious underlying illnesses that help contribute to their presentation, and it is imperative to aggressively identify and treat these conditions.

  • Resuscitative efforts should not be terminated until defibrillation remains unsuccessful despite a rewarmed core body temperature of at least 32°C.

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Introduction

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Clinical hypothermia is defined as a core body temperature of less than 35°C (95°F) and can be clinically stratified by the core temperature into mild (35°–32°C/95°–89.6°F), moderate (32°–30°C/89.5°–86°F), and severe (<30°C/86°F) subtypes. Hypothermia occurs as the body loses heat from 1 of 4 major mechanisms: conduction, convection, evaporation, and radiation. Convective (windy environments) and conductive (cold and wet exposures) mechanisms are responsible for most cases of accidental hypothermia. Hypothermia can be further classified as either primary or secondary. Primary hypothermia occurs when an otherwise healthy person is unable to compensate for an excessive exposure to cold temperatures. Secondary hypothermia occurs when a comorbid medical condition (eg, hypothyroidism, sepsis, intoxication) disrupts a patient's normal thermoregulatory processes.

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Although most common in colder climates, hypothermia can occur in any environment. Case reports during summer months and in hospitalized patients are not uncommon. In the United States, hypothermia is responsible for approximately 700 deaths annually,with more than half occurring in patients older than 65 years. Patients with an initial core body temperature <23°C (73.4°) typically do not survive, and the overall mortality rate of patients with hypothermia is approximately 40%.

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Clinical Presentation

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History

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The potential for hypothermia is usually obvious in patients with significant exposures. Patients may present in wet clothing, be found outdoors in the cold weather, or be inappropriately dressed for the environment in which they live. In the UnitedStates, most hypothermic patients are either intoxicated or suffer from an underlying psychiatric illness or dementia.

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The history or presentation may be less obvious for patients with mild hypothermia or unknown exposures. Said patients typically present with nonspecific neurologic findings, including dizziness, confusion, slurred speech, or ataxia. Patients with severe hyperthermia may present comatose or in cardiac arrest.

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Physical Examination

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As with all emergency department (ED) patients, start by assessing and addressing the patient's airway, breathing, and circulation (ABCs) and vital signs. Hypothermic patients may present with unstable airways or absent pulses. Carefully measure the patient's core body temperature by inserting a specialized “low-reading” probe into the bladder, rectum, or esophagus as this will be pivotal to establish the diagnosis. Keep in mind that the majority of standard ED thermometers will not record temperatures below 34.4°C (94°F).

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Physical exam findings frequently vary based on the degree of hypothermia. It is imperative to immediately and completely undress the patient to remove any wet clothing and identify any signs of coexisting frostbite, trauma, sepsis, hypothyroidism, adrenal crisis, toxidromes, or cardiac dysfunction. Refrain from any unnecessary movement of the patient to avoid precipitating life-threatening dysrhythmias, as hypothermic myocardium is exceptionally irritable. Finally, perform a comprehensive neurologic exam including an evaluation for level of consciousness, pupillary reactivity, and focal deficits. The following describes findings specific to varying degrees of hypothermia.

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Mild Hypothermia
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Patients tend to present with shivering, tachycardia, tachypnea, and hyperventilation. As their core temperature approaches 33°C (91.4°F), ataxia and apathy begin to develop.

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Moderate Hypothermia
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