Hospital Medicine

Hypothermia

I. What every physician needs to know.

Accidental hypothermia is defined as a reduction in core body temperature below 95 °F (35 °C). It is further subdivided into three grades:

  • Mild 32–35 °C (90–95 °F)

  • Moderate 28–32 °C (82–90 °F)

  • Severe <28 °C (<82 °F)

The etiology of accidental hypothermia is often multifactorial. The most common contributing factors are cold exposure, use of depressant drugs (such as alcohol and benzodiazepines) and hypoglycemia.

Alcohol is by some estimates a contributing cause in more than 50% of cases of hypothermia. Alcohol impairs the perception of cold, impairs judgment, and increases heat loss through peripheral vasodilation. Most sedative-hypnotics can also contribute to hypothermia by reducing shivering as well as impairing the patient's ability to take voluntary actions to reduce heat loss.

Causes of hypothermia

Hypothermia can be considered primary (when heat production is simply overcome by an excessively cold environment in an otherwise healthy individual) or secondary (due to medical condition(s) that either impair thermoregulation or increase heat loss). Causes of secondary hypothermia include:

Impaired thermoregulation

  • Central nervous system (CNS) disorders

    • Stroke

    • Intracranial neoplasm

    • Wernicke-Korsakoff syndrome

    • Anorexia nervosa

    • Parkinson's disease

    • Hypothalamic dysfunction

    • Subarachnoid hemorrhage

    • CNS trauma

  • Endocrine disorders

    • Diabetic ketoacidosis (DKA) or hyperosmolar coma

    • Hypothyroidism

    • Panhypopituitarism

    • Adrenal insufficiency

  • Drugs

    • Alcohol, barbiturates, paralytic agents

  • Sepsis

  • Renal failure

  • Liver failure

  • Insufficient energy

    • Extreme physical exertion

    • Malnutrition

    • Hypoglycemia

Increased heat loss

  • Exposure to cold

    • Accidental (inadequate shelter and clothing, immobility)

    • Iatrogenic (includes causes such as operating rooms, inadvertent perioperative hypothermia, infusion of cool fluids or blood products and continuous ultrafiltration at low rates)

    • Impaired behavioral response to cold (cognitive impairment, intoxication, encephalopathy)

  • Skin disorders

    • Psoriasis

    • Extensive third degree burns

  • Inappropriate peripheral vasodilation

    • Peripheral neuropathy

    • Spinal cord injury

  • Trauma

II. Diagnostic Confirmation: Are you sure your patient has hypothermia?

Diagnosis is confirmed by measuring core body temperature (rectal, esophageal or bladder). The use of low temperature thermometers is encouraged as most commonly used clinical thermometers do not measure accurately below 94 °F (34.4 °C).

A. History Part I: Pattern Recognition:

The diagnosis of hypothermia is usually suggested by a history of cold exposure or immersion. Mental status changes vary greatly from patient to patient, but some degree of confusion or lowered level of consciousness is often seen even with mild hypothermia.

High-risk patients, as noted below, can present with hypothermia even without significant cold exposure as well as with atypical exam findings. A high index of suspicion is needed in such cases to ensure appropriate treatment is initiated early.

B. History Part 2: Prevalence:

Hypothermia is estimated to account for approximately 0.01% of the annual 110 million emergency department visits in the United States. Hypothermia related admissions occur throughout the year and peak during February. High-risk patients include those who are elderly, alcoholic, and diabetic; trauma patients; and those who are severely debilitated or cognitively impaired.

D. Physical Examination Findings.

  • Vital signs: Hypothermic patients may present with profound bradycardia. If not immediately detected, the pulse should be checked for a full 60 seconds before proceeding to cardiopulmonary resuscitation. In addition, hypotension and hypopnea may be present.

  • Mental status: Mental status changes vary greatly from patient to patient. Some degree of confusion or lowered level of consciousness is common with mild hypothermia. Early signs include weakness, confusion and ataxia. (Neurologic changes are sometimes referred to as the "umbles": fumbles, mumbles, stumbles, and crumbles.) In severe hypothermia, patients invariably have markedly lowered levels of consciousness and often are able to respond purposefully only to noxious stimuli ("crumbles").

  • Respiratory: Both tidal volumes and respiratory rate are reduced with increased levels of hypothermia.

  • Cardiovascular: Atrial fibrillation is common in moderate hypothermia; the risk of ventricular arrhythmias and cardiac arrest increases in particular with severe hypothermia, but can be seen in moderate cases as well.

  • GI: Ileus is a common finding in hypothermia and in moderate-to-severe hypothermia is almost universal.

  • Musculoskeletal: Shivering is usually seen in mild hypothermia but can be greatly impaired due to a long list of confounding factors including recent alcohol use or use of sedative-hypnotics. In moderate hypothermia, shivering decreases dramatically; shivering is often absent at temperatures below 30 °C.

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Admission blood work should include fingerstick glucose, complete blood count (CBC), chemistry panel, liver function tests (LFTs), amylase and lipase. An EKG should be obtained. The following tests should be considered in specific situations:

  • Thyroid function tests if the etiology of hypothermia is unclear or appears out of proportion to precipitating event

  • Blood cultures, urinalysis and urine cultures, chest X-ray if an infectious etiology suspected

  • Arterial blood gas (acidosis can provide prognostic information).

A. Immediate management

  • ABCs to ensure patent airway, pulse and cardiovascular perfusion.

  • Wet clothing should be removed and replaced by a warm bed, blankets and insulation from heat loss.

  • A full survey for any evidence of trauma or peripheral cold injury (chilblain or frostbite) should be performed.

  • Core temperature should be monitored with a low-read thermometer.

  • Dehydration is almost inevitably present with hypothermia and should be treated with warmed intravenous fluids (38-42 °C) prior to rewarming to minimize the risk of organ infarction or "afterdrop" (recurrent hypothermia). Normal saline is preferred over Lactated Ringer's solution given theoretical concerns for decreased liver function with hypothermia, though providers should be cautious not to exacerbate acidosis when present. Substantial amounts of fluid may be needed due to the effects of cold diuresis and peripheral vasodilation during rewarming.

  • Continuous cardiac monitoring should be instituted in moderate or severe cases. Hypothermic patients remain at significant risk for ventricular arrhythmias and rough handling and unnecessary stimulation or movement should be avoided.

  • If hypoglycemia is present, 25-50 mg of glucose as a D50 solution should be given.

  • If altered mental status is present, consider IV thiamine (100 mg), dextrose (25 mg) and naloxone (0.4 mg)

  • Consider empiric antibiotics in geriatric or immunocompromised patients.

B. Definitive Management

Further rewarming should be directed by the severity of the hypothermia. Rewarming methods include passive external, active external, minimally invasive, and invasive central rewarming.

  • Passive external rewarming is usually sufficient for mild hypothermia. This method centers around preventing further heat loss. After the patient’s clothes are removed, blankets and insulating materials are applied, allowing the patient’s own intrinsic heat production to warm the body.

  • Active external rewarming is usually needed in cases of moderate hypothermia or when the patient lacks the necessary physiological reserve to rewarm their body. Active external rewarming refers to the application of heat directly to the body through heating pads, warming blankets (Behr Huggers®), radiant heat or warm baths. Active external rewarming may predispose patients to hypovolemic shock and ventricular fibrillation as a result of peripheral vasodilation and "afterdrop" (a drop in the core temperature that results when cold blood that has pooled in the extremities returns to the core as a result of peripheral warming and vasodilation). In addition, care should be taken to avoid burning the skin.

  • Minimally invasive rewarming consists of infusion of warmed intravenous fluids. This method plus active external rewarming is typically used in cases of moderate hypothermia.

  • Invasive central rewarming is often needed for patients with severe hypothermia and reduces the risk of "afterdrop". It is the fastest but most invasive therapeutic strategy available. Extra-corporeal blood warming (through cardiopulmonary bypass or less often aterio-venous or venous-venous extracorporeal membrane oxygenation) is the treatment of choice. Cardiopulmonary bypass or arterio-venous ECMO should be employed in patients with cardiac instability refractory to medical management who require cardiac support. Other methods of central rewarming include warmed and humidified oxygen delivered by face mask or endotracheal tube, hemodialysis, thoracic lavage, and peritoneal lavage or dialysis with fluid heated to 38 to 43 °C and exchanged every 20 minutes.

In addition to rewarming, efforts should be undertaken to identify and treat the underlying cause(s) of the patient's hyperglycemia.

B. Anticipated Length of Stay.

Length of stay varies greatly depending on the patient population studied and precipitating event. Hypothermia has been shown to be independently associated with increased length of stay for patients admitted with sepsis, for severely injured trauma patients, and for general surgery populations (due to inadvertent perioperative hypothermia).

F. Prognosis and Patient Counseling.

Estimates for the mortality rate of treated hypothermia are wide and range from 12% to 73% depending on the population studied. The prognosis of hypothermia depends heavily on the age of the patient and the etiology and severity of the hypothermia. Young adults with mild hypothermia usually recover without any lasting sequelae. The mortality rate for elderly patients (> 70 years old) with moderate-to-severe hypothermia (T < 32 °C) has been estimated to be greater than 50%. Patients who experience cardiac arrest and require extracorporeal rewarming have a survival rate of approximately 50%.

In patients with cardiac arrest due to hypothermia who have been warmed to greater than 35 °C and remain in asystole, the likelihood of return of spontaneous circulation is low and cessation of CPR should be considered. In addition, very elevated serum potassium is a poor prognostic marker (as it indicates that hypoxia was present before cooling). If the serum potassium is greater than 12 mmol/L, cessation of CPR should be considered.

A. Core Indicator Standards and Documentation.

None

B. Appropriate Prophylaxis and Other Measures to Prevent Readmission.

  • Prophylaxis: Most patients with hypothermia do not require any disease specific prophylactic measures. Those patients with impaired mental status are, however, at high risk for both pressure ulcers and aspiration pneumonia; standard precautions should be exercised to prevent these complications.

  • Discharge planning to prevent readmissions: Since hypothermia can have a large number of precipitants, discharge planning should center around the specific events that led to the episode of hypothermia. Common issues reviewed before discharge include social support networks, substance abuse, psychiatric comorbidities, housing and shelter options as well as home heating (household temperatures below 65 °F are associated with hypothermia in older adults).

What's the evidence?

Brown, D,, Brugger, H,, Boyd, J,, Paal, P:. "Accidental hypothermia.". N Engl J Med. vol. 367. 2012. pp. 1930-8.

Epstein, E,, Anna, K:. "Accidental hypothermia.". BMJ. vol. 25. 2006. pp. 706-709.

Guly, H:. "History of accidental hypothermia.". Resuscitation. vol. 82. 2011. pp. 122-125.

Headdon, WG,, Wilson, PM,, Dalton, HR:. "The management of accidental hypothermia.". BMJ. vol. 338. 2009. pp. b2085.

Petrone, P,, Asensio, JA,, Marini, CP:. "Management of accidental hypothermia and cold injury.". Curr Probl Surg.. vol. 51. 2014. pp. 417-31.

Saxena, P,, Shehatha, J,, Boyt, A,, Newman, M,, Konstantinov, IE:. "Role of extracorporeal circulation in the management of accidental deep hypothermia.". Heart Lung Circ. vol. 18. 2009. pp. 416-418.

Vanden, HTL,, Morrison, LJ,, Shuster, M,, Donnino, M,, Sinz, E,, Lavonas, EJ,. "Part 12: cardiac arrest in special situations: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.". Circulation. vol. 122. 2010. pp. S829-61.

Wira, CR,, Becker, JU,, Martin, G,, Donnino, MW:. "Anti-arrhythmic and vasopressor medications for the treatment of ventricular fibrillation in severe hypothermia: a systematic review of the literature.". Resuscitation. vol. 78. 2008. pp. 21-29.

Van der Ploeg, GJ,, Goslings, JC,, Walpoth, BH,, Bierens, J:. "Accidental hypothermia: Rewarming treatments, complications, and outcomes from one university medical centre.". Resuscitation. vol. 81. 2010. pp. 1550-1555.

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