- A core temperature of less than 35°C (95°F)
- May take several hours to days to develop
- Patients with cold water immersion can appear to be dead but can still be resuscitated.
- System(s) affected: All body systems
- Synonym(s): Accidental hypothermia
- Predominant age: Very young and the elderly
- Predominant sex: Male > Female
More common due to lower metabolic rate, impaired ability to maintain normal body temperature, and impaired ability to detect temperature changes
Estimates vary widely due to lack of pathologic evidence, and it is usually considered a secondary cause in diagnosing disorders.
- Alcohol consumption
- Cardiovascular disease
- Cold water immersion
- Dermal dysfunction (burns, erythrodermas)
- Drug intoxication
- Endocrinopathies (myxedema, severe hypoglycemia)
- Excessive fluid loss
- Hepatic failure
- Hypothalamic and central nervous system (CNS) dysfunction
- Mental illness; Alzheimer disease
- Prolonged environmental exposure
- Renal failure
- Trauma (especially head)
- Appropriate clothing with particular attention to head, feet, and hands
- For outdoor activities, carry survival bags with space blankets for use if stranded or injured.
- Avoid alcohol.
- Alertness to early symptoms and initiating preventive steps (e.g., drinking warm fluids)
- Identify medications that may predispose to hypothermia (e.g., neuroleptics, sedatives, hypnotics, tranquilizers).
- Overwhelming environmental cold stress
- Decreased heat production
- Increased heat loss
- Impaired thermoregulation
Commonly Associated Conditions
- Addison disease
- CNS dysfunction
- Congestive heart failure
- Pulmonary infection
Presentation varies with the temperature of the patient at the time of presentation.
History of prolonged exposure to cold may make the diagnosis obvious, but hypothermia may be overlooked, especially in comatose patients.
Exam findings vary with the temperature of the patient at the time of presentation:
- Mild (32°C–35°C):
- Lethargy and mild confusion
- Loss of fine motor coordination
- Increased blood pressure
- Peripheral vasoconstriction
- Moderate (28°C–32°C):
- Arrhythmias (prolonged PR interval; AV junctional rhythm; idioventricular rhythm; prolonged QT interval; altered T waves)
- Semicoma and coma
- Muscular rigidity
- Generalized edema
- Slowed reflexes
- Severe (<28°C):
- Very cold skin
- No pulse: Ventricular fibrillation or asystole
- Fixed pupils
Use specially designed thermometers that can record low temperatures and measure core temperatures.
- Infants may present with bright red, cold skin and very low energy.
- A child’s body temperature drops faster than an adult’s when immersed in cold water.
Diagnostic Tests & Interpretation
Initial lab tests
- Arterial blood gases (corrected for temperature)
- Complete blood and platelet counts
- Serum electrolytes
- Coagulation studies
- Fibrinogen levels
- Blood culture
- Blood urea nitrogen/creatinine
- Liver function studies
- Cardiac enzymes
- Alcohol level
Follow-Up & Special Considerations
- Toxicology screen if mental status changes are more extreme than expected for temperature decrease
- Serum cortisol, if indicated
- Thyroid function tests, if indicated
Cervical spine, chest, abdomen, if appropriate
- Moderate dilation of right heart
- Pulmonary edema
- Cerebrovascular accidents
- Drug overdose
- Complications of diabetes, hypothyroidism, hypopituitarism
- For sepsis or bacterial infections: Antibiotics based on site and etiology (1)[C]
- For hypoglycemia, D50W at a dose of 1 mg/kg
- Thiamine, 100 mg, if alcoholic or cachectic
- Naloxone, 2.0 mg
- Levothyroxine 150–500 µg for myxedema
- For severe acidosis: Sodium bicarbonate
- Medications, including epinephrine, lidocaine, and procainamide, can accumulate to toxic levels if used repeatedly.
- Routine use of steroids or antibiotics has not been shown to increase survival or decrease postresuscitative damage.
- Medications should be avoided until core temperature is >30°C:
- When temperature reaches >30°C, IV medications are indicated, but at longer than the standard intervals.
- Avoid vasopressors due to arrhythmogenic potential and delayed metabolism.
- Medications should be avoided until core temperature is >30°C:
- Significant possible interactions:
- Use all drugs cautiously due to impaired metabolism and renal elimination.
- Once rewarming has occurred, there is mobilization of depot stores.
- Pre-hospital (2)[C]:
- ABCs of basic life support
- Remove wet garments.
- Protect against heat loss and wind chill.
- Give warm humidified oxygen if available.
- See Initial Stabilization
Rewarming dependent on severity of hypothermia and presence of cardiac arrest:
- If no cardiac arrest, consider active external rewarming (3)[B].
- If cardiac arrest present, consider active internal rewarming (3)[B].
- Warm center of body first.
- The rate of rewarming is determined by whether a perfusing cardiac output is present:
- If a perfusing cardiac output is present, 1–2ºC per hour is appropriate.
- If not, then a faster rate of >2ºC per hour should be used.
- Monitor core temperature; use a consistent method.
- Monitor blood pressure and cardiac rhythm.
- Correct metabolic acidosis.
- Evaluate for frostbite and other trauma.
- Mild hypothermia:
- Passive rewarming
- Administration of heated IV solutions (D5NS)
- Warm fluids may be given if fully alert.
- Moderate hypothermia:
- Active external rewarming with forced warm air systems (4)[B]
- Severe hypothermia (active internal [core] rewarming):
- Minimally invasive
- Heated IV fluids
- Heated humidified oxygen
- Body cavity lavage:
- Thoracic cavity lavage (43°C)
- Gastrointestinal, colonic, or bladder lavage with warm fluids (43°C)
- Peritoneal dialysis
- Extracorporeal blood rewarming (4)[B]:
- Cardiopulmonary bypass
- Extracorporeal membrane oxygenation
- Continuous arteriovenous rewarming
- Hemodialysis and hemofiltration
- Cardiac arrhythmias:
- Atrial fibrillation and sinus bradycardia are common, but patients usually convert to normal sinus rhythm with rewarming.
- If ventricular fibrillation is present, it should be treated with 1 shock. If patient does not respond, further attempts should be deferred until the patient is rewarmed (1)[B].
- Do not treat transient ventricular arrhythmias.
- If cardiac pacing required, preferable to use external noninvasive pacemaker
Patients with underlying disease, physiologic abnormalities, or core temperature 32°C should be admitted, preferably to intensive care unit (1)[A].
IVs should be heated to 40°C–42°C when possible, but should be no colder than the patient’s core temperature.
- Avoid fluid overload.
- Avoid lactated Ringer solution because of decreased lactate metabolism.
Because of the cold, heart is irritable and susceptible to arrhythmias; take special care in moving and transporting.
Discharge from emergency department once normothermic, if mild hypothermia and no predisposing conditions or complications, and has suitable place to go.
- During acute episode:
- Monitor cardiac rhythm.
- Monitor electrolytes and glucose frequently.
- Monitor urinary output.
- Follow blood gases.
- Following acute episode:
- Continued therapy for any underlying disorder
Warm fluids only, if alert and able to swallow
- Alcohol intake increases risk of becoming hypothermic in cold conditions.
- Encourage persons with cardiovascular disease to avoid outdoor exercise in cold weather.
- If appropriate, referral to social service agency for help with adequate housing, heat, or clothing.
- Mortality rates are decreasing due to increased recognition and advanced therapy.
- Mortality usually dependent on the severity of underlying cause of hypothermia
- In previously healthy individuals, recovery is usually complete.
- Mortality rate in healthy patients is <5%.
- Mortality rate in patients with coexisting illness is >50%.
- Mortality rates increase with increasing age.
- Cardiac arrhythmias
- Bladder atony
- Pneumonia (aspiration and broncho)
- Pulmonary edema
- Acute respiratory distress syndrome
- Gastrointestinal bleeding
- Acute tubular necrosis
- Intravascular thromboses/disseminated intravascular coagulation
- Metabolic acidosis
- Gangrene of extremities
- Compartment syndromes
1. Guvakov D, Weiss S, Cheung A. Hypothermia. ACP PIER: The Physicians’ Information and Education Resource. 2008.
2. American Heart Association. Part 10.4: Hypothermia. Circulation. 2005;112:IV-136–IV-138.
3. Kempainen RR, Brunette DD. The evaluation and management of accidental hypothermia. Respir Care. 2004;49:192–205.
4. McCullough L, Arora S. Diagnosis and treatment of hypothermia. Am Fam Physician. 2004;70:2325–32.
Headdon WG, Wilson PM, Dalton HR et al. The management of accidental hypothermia. BMJ. 2009;338:b2085.
Schweitzer KS. Cold but not dead. Air Med J. 2008;27:94–8.
See Also (Topic, Algorithm, Electronic Media Element)
Frostbite; Near Drowning
386689009 Hypothermia (finding)
- Most common cause of hypothermia in US is cold exposure due to alcohol intoxication
- As long as core temperature is severely decreased, one should not assume that resuscitation is not possible unless there are obvious lethal injuries (“not dead until warm and dead”).
- Electrocardiogram changes are associated with hypothermia.
- Slowing of sinus rate with T-wave inversion
- QT-interval prolongation
- Hypothermic J waves (Osborn waves) characterized by a notching of the QRS complex and ST segment