| General |
Definition: core temperature lower than 35°C (95°F) - Mild: 32 to 35°C (90 to 95°F)
- Moderate: 28 to 32°C (82 to 90°F)
- Severe: below 28°C (82°F)
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| In patients who are not completely alert and oriented, measure core temperature with a low-reading, digital temperature probe if available. Measure esophageal temperature in patients with tracheal tube or supraglottic airway in place.* Standard oral thermometers do not read below 34°C (93°F). |
| Consider hypothermia secondary to other conditions (eg, infection, hypoglycemia, adrenal insufficiency, hypothyroidism, overdose, trauma). Older adults are at higher risk. Hypothermia with associated comorbidities or trauma is considered more severe. |
| Clinical aspects |
Physical examination - Vital signs
- Mild hypothermia: tachypnea, tachycardia, hyperventilation
- Moderate hypothermia: expect bradycardia (tachycardia suggests hypoglycemia, hypovolemia, or overdose), hypotension, hypoventilation
- Severe hypothermia: hypotension, cardiovascular collapse
- Neurological examination
- Mild hypothermia: ataxia, dysarthria, impaired judgement; suspect CNS pathology if patient comatose
- Moderate hypothermia: CNS depression
- Severe hypothermia: areflexia, coma
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| Laboratory evaluation |
For patients with moderate or severe hypothermia, studies to obtain include: fingerstick glucose, coagulation studies, CBC, basic electrolytes, BUN and creatinine, serum lactate, electrocardiogram, plain chest radiograph. Additional studies may be needed. - Clinical coagulopathy may be present despite normal measured coagulation times
- Increased hematocrit may reflect hemoconcentration
- May see low bicarbonate, suggesting anion-gap acidosis; if so, obtain venous or arterial blood gas
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Electrocardiogram - Rhythm abnormalities (atrial fibrillation, sinus bradycardia) may be present
- Intervals (PR, QRS, and QTc) may be prolonged
- Osborn J waves are characteristic of hypothermia (but can occur with other conditions)
- Occur at junction of QRS and ST segments, most prominent in V2 to V5
- Distortion of the earliest phase of membrane depolarization
- Computer may misinterpret as ischemic injury pattern
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| Treatment |
| Endotracheal intubation may be necessary in obtunded or unconscious patients and those with bronchorrhea |
| Treat hypotension with warmed, isotonic crystalloid (40 to 42°C) initially, vasopressors (norepinephrine preferred) if necessary |
| Avoid rough movements and activity, which may induce ventricular fibrillation |
Rewarming techniques are based on degree of hypothermia - Mild hypothermia
- Remove wet clothing, cover with warm blankets, keep room temperature at approximately 28°C (82°F).
- Provide active external rewarming, with forced air warming systems if available. Warmed blankets, heating pads, radiant heat sources can also be used. Avoid burning skin.
- Moderate hypothermia
- Provide active external rewarming as described above.
- Give warmed IV fluids (40 to 42°C) and warmed humidified oxygen as adjuncts (these are not primary rewarming methods).
- Beware of afterdrop, a drop in core temperature caused by return of cold blood from the extremities to the core circulation. Rewarm trunk first to minimize afterdrop.
- Severe hypothermia: active external rewarming and active internal rewarming (active core rewarming)
- Perform interventions for moderate hypothermia.
- For hemodynamically stable patients, rewarm with endovascular temperature catheter whenever available.
- For hemodynamically unstable patients, rewarm with ECMO (preferred approach) or CPB if possible. If ECMO or CPB not available, can perform continuous venovenous rewarming, hemodialysis, continuous arteriovenous rewarming.
- If other interventions unavailable, may perform peritoneal or pleural irrigation with warmed, isotonic saline (40 to 42°C).
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Treatment of arrhythmias - Arrhythmias may persist until patient rewarmed
- Ignore atrial arrhythmias with slow ventricular response
- Ventricular fibrillation is common rhythm
- Electrical defibrillation may be attempted but is rarely successful until core temperature is above 30°C.
- Initiate CPR in all patients with cardiac arrest; do not perform chest compressions if an organized rhythm is present on the cardiac monitor.*
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