Update June 22, 2022
Accidental hypothermia occurs when there is an unintentional drop in the body’s core temperature below 35°C (95°F). At this temperature, many of the compensatory physiologic mechanisms that conserve heat begin to fail.
Primary accidental hypothermia is a result of the direct exposure of a previously healthy individual to the cold.
[ The mortality rate is much higher for patients who develop secondary hypothermia as a complication of a serious systemic disorder.]
In extreme temperatures, the body’s thermoregulation may fail. This results in the core body temperature moving toward the temperature of the external environment.
The likelihood and severity of extreme temperature-related conditions depend on physiologic and environmental factors. Physiologic risk factors include extremes of age; cognitive impairment; poor physical conditioning/sedentary lifestyle or immobility; poor acclimatization; concurrent injury; prior temperature-related injury, and numerous underlying medical conditions, especially those affecting cognition and thermoregulation.
Underlying medical conditions include cardiopulmonary, vascular, neurologic, psychiatric, musculoskeletal, immunologic, hematologic, endocrine [hypothyroidism, adrenal insufficiency, hypopituitarism], renal, hepatic, skin, and infectious diseases.
Pharmacologic risk factors include medications, holistic or alternative treatments, illicit drugs, tobacco, and alcohol. There is a subset of medications associated with a particularly high likelihood of worsening temperature-related conditions, such as those that impact sweating and the central nervous system (ie, anticholinergics, stimulants, and sedatives) and those that affect cutaneous blood flow such as peripheral vasoconstrictors or vasodilators.
Environmental risk factors include changing weather conditions (wind, rain, snow, etc.), inadequate clothing or housing (homelessness, or housing, with inadequate temperature control), and occupational or recreational exposure.
Low body temperature impairs cellular metabolism and brain function, particularly judgment, and the combination prevents protection from continued exposure leading to fatal hypothermia.
Hypothermia also protects the tissues from ischemic injury, so complete recovery is possible from rapid and sustained cooling even when the patient appears clinically dead. This is especially true for cold water immersion (drowning). Relative or absolute hypothermia in situations where fever would be expected (e.g., severe infection) is a poor prognostic sign. Core temperature is usually lower in older adults making them particularly susceptible to decreased environmental temperatures.
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A 48-year-old man is brought to the emergency department in January after being found unresponsive in a city park. He suffers from alcoholism and was last seen by his daughter about 12 hours before being brought to the emergency department. At that time, he left their home intoxicated and agitated. He left seeking additional alcohol as his daughter had poured out his last bottle of vodka hoping that he would seek treatment. On presentation, he has a core body temperature of 88.5°F (31.4°C), heart rate of 48 bpm, respiratory rate of 28/min, and blood pressure of 88/44 mmHg; oxygen saturation is unable to be obtained. The arterial blood gas demonstrates a pH of 7.05, PaCO2 of 32 mmHg, and PaO2 of 56 mmHg. Initial blood chemistries demonstrate a sodium of 132 mEq/L, potassium of 5.2 mEq/L, chloride of 94 mEq/L, bicarbonate of 10 mEq/L, blood urea nitrogen (BUN) of 56 mg/dL, and creatinine of 1.8 mg/dL. Serum glucose is 63 mg/dL. The serum ethanol level is 65 mg/dL. The measured osmolality is 328 mOsm/kg. ECG demonstrates sinus bradycardia with a long first-degree atrioventricular block and J waves. In addition to initiating a rewarming protocol, what additional tests should be performed in this patient?
The correct answer is D. You answered D.
The answer is D. When evaluating a patient with hypothermia, it is important to consider all the possible factors that could contribute to hypothermia because treatment of hypothermia alone without treating the underlying cause could lead to delayed diagnosis and poor outcomes. In some instances, it is clear that the cause of hypothermia is simply prolonged exposure to cold without proper clothing. However, in patients such as this one, the clinician will need to look for findings that would be unexpected in a hypothermic patient. This patient has a moderate degree of hypothermia (between 28.0°C and 32.2°C). At this range of hypothermia, the expected clinical presentation would be one of a global slowing of metabolism. Clinically, this would include a depressed level of consciousness with papillary dilatation. Often these individuals experience a paradoxical instinct to take off their clothes. In addition, the heart rate, blood pressure, and respiratory rate would be expected to decrease. Carbon dioxide production by tissues typically decreases by 50% for each 8°C drop in body temperature. A common error in the treatment of hypothermic individuals is overly aggressive hyperventilation in the face of this known decrease in carbon dioxide production. In this patient, despite the hypothermia, there is an increased respiratory rate in the setting of a metabolic acidosis. This finding would suggest a lesion in the central nervous system or ingestion of an alcohol that would lead to a metabolic acidosis. Ingestion is confirmed by the presence of a very high anion gap (28) as well as an osmolar gap. The osmolar gap can be calculated as: (sodium × 2) + (BUN/2.8) + (glucose/18) + (ethanol/4.6). In this patient, the calculated osmolarity would be 301.6. Thus, the osmolar gap is 26, indicating the presence of some other osmotically active compound. In this case, it is prudent to measure toxic alcohol levels such as methanol and ethylene glycol. In the management of the patient’s hypothermia, warmed intravenous fluids may be indicated. However, the lactated Ringer’s solution should be avoided as the liver may be unable to metabolize lactate, which could lead to worsening metabolic acidosis. The cardiac complications of hypothermia may lead to bradyarrhythmias, but cardiac pacing is rarely indicated. If required, the transthoracic route is preferred because placement of any leads into the heart may lead to refractory ventricular arrhythmias.
Reperfusion of extremities in hypothermia can cause all of the following EXCEPT:
The correct answer is B. You answered B.
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