Hypothermia and frostbite

Last updated: August 12, 2022

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Hypothermia is defined as a drop in core body temperature below 35°C (95°F). Impaired thermoregulation, decreased heat production, and increased heat loss can contribute to accidental hypothermia. Hypothermia is classified as mild, moderate, or severe based on core body temperature and clinical features, which range from shivering to progressive bradycardia, coma, and circulatory collapse. During the diagnostic assessment, the patient's core body temperature should be determined first, followed by an ECG. Further testing assesses for comorbidities and complications. Treatment involves rewarming and supportive care. Cardiac arrhythmias are the most common cause of death in hypothermia. Frostbite is a tissue injury that can occur after exposure to freezing temperatures and typically affects the face, ears, fingers, and/or toes; frostbite can occur with or without hypothermia. Mild frostbite is reversible, while severe cases may require amputation. Nonfreezing cold injuries are typically less severe and include immersion injuries, panniculitis, cold urticaria, and pernio.

See “Targeted temperature management” for details about therapeutic hypothermia.

Primary (environmental exposure to cold) or secondary (underlying condition with inadequate temperature regulation) etiologies which result in:

Mechanisms of heat loss
Mode of heat transfer Definition Comments
Evaporation
  • Loss of energy due to a phase transition of water on the surface of the skin or mucous membranes from the liquid phase to the gaseous phase
  • Evaporation is the most effective mechanism for dissipating heating from the body during intense exercise and in hot and dry environments
  • Evaporative heat loss cannot occur if the ambient relative humidity is 100%
Conduction
  • Heat transfer that occurs as a result of a transfer of kinetic energy between molecules
  • Most prominent when a person lies on a cold surface
Convection
  • Heat transfer that occurs as a result of the macroscopic movement of a fluid
  • Occurs when an individual is immersed in flowing water or when the air is continuously circulated (e.g., air-conditioned room)
Radiation
  • Energy transfer in the form of electromagnetic waves (e.g., infrared waves)
  • Radiation is the only mode of heat transfer in a vacuum
  • Radiation is the main mode of heat loss in a cool environment (< 20°C) with no wind

References:[1][2]

  • The body loses heat through radiation; (most significant means of heat loss), conduction, convection, and direct contact with cold surfaces.
  • The hypothalamus attempts to maintain a temperature of approximately 36.5°C (97.7°F) to 37.5°C (99.5°F) by:
  • Hypothermia affects all organ systems
    • General tissue oxygen demand decreases by ∼ 6% per degree Celsius below 35°C.
    • Weakened cellular immune response
    • Cardiovascular effects: depolarization of cardiac cells → ↓ cardiac output and ↓ mean arterial pressure
    • CNS effects: CNS metabolism

References:[2][3]

Definition [4]

Accidental hypothermia: an involuntary drop in core body temperature below 35°C (95°F)

Clinical features of hypothermia [5][6]

Clinical findings, including level of consciousness (LOC), correlate with core body temperature, and together can be used to define stages of hypothermia. [7][8][9]

Mild hypothermia (32–35°C/ 89.6–95.0°F)

Moderate hypothermia (28–32°C/ 82.4–89.6°F)

The presence or absence of shivering does not accurately reflect the stage of hypothermia.

Severe hypothermia (< 28°C/ < 82.4°F)

Diagnostics [5][11]

Approach

  • All patients: Measure core temperature and determine the stage of hypothermia. [6]
    • First-line: esophageal temperature probe
    • Second-line: rectal or bladder thermometer
    • Avoid tympanic or oral thermometers, as they do not reflect core temperature.
  • Moderate or severe hypothermia
  • Trauma patients: Obtain imaging to evaluate concomitant injuries.

Consider alternate diagnoses (e.g., sepsis or stroke) if the clinical features are inconsistent with the body temperature (e.g., coma at a core temperature of 32°C).

ECG [12]

Routine laboratory studies [5][11][13]

Obtain basic laboratory studies to rule out complications and guide resuscitation. Typical findings include:

Use clinical findings to guide management, as cold and/or rewarmed blood samples may yield inaccurate results (e.g., due to hemolysis). [11]

The lethal triad of hypothermia, acidosis, and coagulopathy is associated with poor outcomes in patients with cold exposure and severe trauma. [14]

Additional laboratory studies [5]

Consider the following to identify underlying etiologies or differential diagnoses:

Imaging [5]

Management of hypothermia [4][5][6]

Initial resuscitation: ABCDE approach

Rewarming techniques [4][5][17]

Passive rewarming

  • Patients with mild hypothermia may only require passive rewarming.
  • Insulation (e.g., with blankets) allows patients to retain body heat.
  • Active movement can increase heat generation.

Active rewarming

If rewarming is unsuccessful, consider the possibility of an underlying infection, endocrine insufficiency, or insufficient resuscitation. [5]

Supportive care [5][17]

  • Handle patients with severe hypothermia gently to avoid precipitating ventricular arrythmias.
  • Identify, treat and prevent disease and treatment complications (see “Complications”).
  • Avoid administering medications in patients with severe hypothermia, if feasible.
  • Avoid oral and intramuscular routes of administration.
  • Identify and treat related trauma and cold injuries; see “Frostbite” and “Management of trauma patients.”

Complications [11]

Hypothermic cardiac arrest [6][9]

Refers to cardiac arrest occurring after the development of hypothermia. Both ventricular fibrillation and asystole can occur spontaneously in severe hypothermia.

Initiate rewarming and do not withhold life-saving treatment from hypothermic patients who appear clinically dead (e.g., dilated pupils, areflexia, rigidity) without signs of irreversible death. [6][9]

Defibrillation is unlikely to be successful at core temperatures < 30°C (86°F). [6]

Other disease complications

Patients with moderate to severe hypothermia may have arrhythmias that are unresponsive to defibrillation. Continue CPR and consider delaying further defibrillation until the patient's core body temperature is > 30°C. [6][15]

Treatment complications

To prevent afterdrop, avoid jostling patients during transport and rewarming the extremities before the core; afterdrop may exacerbate hypothermia and cause arrhythmias. [5]

Disposition

Definition

Severe localized tissue injury; due to freezing of interstitial and cellular spaces after prolonged exposure to very cold temperatures

Clinical features [5][16][17]

General features

  • Frostbite can occur with or without hypothermia.
  • Areas most frequently affected
    • Face (nose, cheeks, chin)
    • Ears
    • Fingers and toes
  • Initial paresthesia is followed by numbness of the affected region.

Features by stage

  • Frostbite is classically staged by degree of injury, similar to burns, but this can be difficult to assess prior to thawing.
  • The simplified staging is easier to apply clinically.
Clinical features and stages of frostbite [17]
Stage Clinical features Tissue loss
Simplified Classic

Superficial or mild frostbite

1st degree
  • Typically none or minimal
2nd degree

Deep or severe frostbite

3rd degree
  • Significant
4th degree
  • Tissue necrosis extending into the muscle, down to the bone

The extent of tissue injury from frostbite is challenging to define initially. Accurate prognosis requires careful observation and may only be possible weeks to months after thawing. [5]

Diagnostics [5][17]

General principles

  • Frostbite is a clinical diagnosis.
  • Measure core temperature in all patients to rule out hypothermia.
  • Consider imaging to evaluate for injury and determine tissue viability.
  • Consider additional diagnostics for patients with concurrent hypothermia or other injuries.

Perform a pulse examination in all patients to assess for an underlying vascular cause (e.g., acute limb ischemia, vascular injury).

Imaging

Management [17][18]

Initial management

  • Remove any wet clothing and jewelry.
  • Ensure that the patient is in a warm environment.
  • Treat hypothermia first, if present (e.g., cover with blankets)
  • Rapid rewarming: Immerse the affected extremity in a warm (37–39°C) circulating water bath. [5]

Refreezing thawed tissue damages it further. If there is a risk of disruption to the thawing process, delay rewarming and keep frostbitten areas dry and insulated. [5]

Prioritize management of hypothermia occurring concurrently with frostbite, as it is both common and life-threatening.

Pharmacotherapy

Wound care

  • Do not debride hemorrhagic vesicles.
  • Change dressings every 6 hours. [5]
  • Drape sterile gauze loosely around thawed areas. [17][18]
  • Elevate the affected limb to decrease edema.
  • Give antibiotics to patients with severe trauma, cellulitis, or signs of sepsis; see “Antibiotics for acute open wounds.” [17]
  • Ensure proper documentation of findings, e.g., with admission photographs.

Supportive therapy

Disposition [5][16][17]

Tissue demarcation (e.g., to guide the need for amputation) may only occur 1–3 months after the frostbite injury. [17]

Complications [11]

  • Loss of sensation
  • Cold hypersensitivity
  • Chronic pain
  • Loss of limb or digits

Immersion injury (trench foot) [5][20][21]

Ischemic and neuropathic damage to the feet due to prolonged exposure to nonfreezing wet conditions

Risk factors

  • Homelessness
  • Substance use
  • Participation in military operations or recreational activities in cold, wet environments

Clinical features

Management

  • Manage hypothermia, if present.
  • Allow the affected limb to air dry and gradually rewarm at room temperature.
  • Provide analgesia as needed and elevate the affected limb. [16][20]
  • Consider a podiatric or surgical consult if there is evidence of tissue necrosis.
  • Prevention: keeping the feet warm and dry

Disposition

  • Admission is commonly necessary for analgesia administration.
  • Discharge considerations
    • Ensure that patients can return to a warm and dry environment.
    • Consider early involvement of social care.

Unlike in frostbite injury, rapid rewarming should not be used for an immersion injury, as this can exacerbate the injury. [16][20]

Perniosis (chillblains) [22][23][24]

A seasonal condition characterized by the inflammation of small blood vessels; triggered by an abnormal reaction to cold and humid conditions

Epidemiology

  • Higher incidence in women
  • More common in individuals who smoke

Etiology

Unknown, but associated conditions include:

Pathophysiology

Clinical features

  • Erythrocyanotic papules or nodules, predominantly on the hands, fingers, toes, legs, and face
  • Lesions appear 12–24 hours after exposure to cold and last for 1–3 weeks.
  • Lesions are accompanied by pain, itching, burning, and/or swelling.
  • In severe cases: blisters, ulcerations.

Diagnostics

Differential diagnoses

Treatment

Panniculitis [11]

  • Mild necrosis of subcutaneous fat caused by prolonged exposure to cold temperatures
  • May result in fat fibrosis, which can cause cosmetic concerns for patients

Cold urticaria [26]

  • Development of urticaria and/or angioedema after brief exposure to cold temperatures
  • The diagnosis is mainly clinical and involves a cold stimulation test.
  • Management includes antihistamines (e.g., loratadine ) and cold avoidance.
  • May be accompanied by cold-induced anaphylaxis
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