Hypothermia is defined as a core (rectal, esophageal, or tympanic membrane) temperature less than 35° C (95 °F). Exposure to cold is usually present but not necessary to produce this condition. An intoxicated swimmer may be in 60 degree Fahrenheit water and may become hypothermic, despite an air temperature of 90°F. Individuals at the extremes of age and those with altered sensorium for any reason are particularly susceptible. It must be considered in any cold exposure with decreased level of consciousness.

The body regulates core temperature through mechanisms of loss and heat gain.

Body Response

Extremes of age, decreased muscle mass, autonomic dysfunction, use of vasoactive drugs such as alcohol predispose hypothermia. Trauma, burns, and other system stressors worsen the body’s response to the cold.

Diagnosis requires measuring a core temperature with a low reading thermometer. Most thermometers read only to 94ºF. A refrigerator thermometer may be shielded and used if necessary. An axillary temp >35.5º C may be useful as a screening tool in a mass casualty situation.

Physical exam and ancillary studies

The physical exam should begin with establishing the airway, breathing, and circulation (ABC’s) and then vital signs to include pulse, blood pressure, respiratory rate, and a core temperature with a hypothermic thermometer (IVAC only reads to 94°F). A mental status may demonstrate signs that are decreased or depressed from normal limits. A screening exam should be completed, including a search for signs of trauma. Baseline studies (if available) should include a CBC (usually hemoconcentrated), electrolytes, BUN, creatinine, glucose (frequently abnormal but not in a predictable manner), ABG, PT/PTT, and if possible, a urine or serum drug tox screen should be considered. An EKG should be done; Osborn (J) waves are a notch at the junction of the QRS complex and ST junction (suggestive but not diagnostic of hypothermia). A chest x-ray is helpful since pneumonia and pulmonary edema are possible complications.

This includes all potential causes of altered mental status and should not be limited to the following conditions:

• Alcohol and other intoxicants

• Endocrine problems

• Hyper/hypoglycemia

• Hypoxemia and narcotics

• Uremia

• Trauma

• Infection, both central nervous system (CNS) and systemic

• Psychiatric problems

• Subarachnoid hemorrhage and space occupying lesions

Treatment includes airway maintenance with respiratory and circulatory support. Avoid rough handling of patient as this may precipitate ventricular fibrillation. Keep the patient supine to avoid orthostatic hypotension. Provide IV (D5 normal saline), supplemental O², and both cardiac and temperature monitoring. Maintain the ABCs and consider axial spine immobilization in suspected trauma cases. Administer warm IV fluids (43ºC) and O2 (42º-46ºC) if the patient’s core temp is < 34° C. Only life-threatening dysrhythmias (ventricular fibrillation (VF) and asystole) should be treated, the remainder will correct with rewarming. The drug of choice for VF is bretylium. Initial defibrillation with up to three attempts is recommended and not re-attempted until core temp reaches 30ºC. Magnesium sulfate has aided spontaneous resolution of VF. Atropine and lidocaine are ineffective in hypothermia. Suspected aspirations should be treated as outlined in the chapter on Immersion Injuries.

Passive external rewarming – place in warm environment, remove wet clothing, and cover with blankets.

Active external rewarming – application of heat to body surface such as hot water bottles (warmed IV bags) in groin and axillas, warmed blankets, and the use of radiant heaters.

• Core temp afterdrop – cold blood returning from the periphery further cools the body core.
• Rewarming acidosis – cold blood returning from the periphery brings lactic acid with it.
• Rewarming shock – relative hypovolemia occurs secondary to peripheral vasodilatation.
• Note: To minimize complications use active, external rewarming in combination with active core rewarming.

Active core rewarming – Method of choice when the temperature is < 30° C or the patient demonstrates cardiac instability.

Non-invasive – warmed humidified O² acts to minimize respiratory heat loss. Warmed intravenous fluid resuscitation (D5 normal saline is preferred).

Invasive – Gastric, colonic, bladder, and peritoneal lavage with warmed normal saline solutions.

• The method of rewarming depends on the core temp and stability of the patient.
• If the patient has a life threatening dysrhythmia you must rapidly and actively rewarm using both invasive and non-invasive techniques.
• Do an initial and secondary exam of all hypothermic patients identifying any trauma or underlying medical conditions.
• In some cases, the patient with severe hypothermia may appear clinically dead. However, in the appropriate setting, resuscitative efforts should continue until the core temperature is at least 86° to 92° F (30 to 33° C). The patient is not expired until warm and expired.

Patients with significant hypothermia/exposure should be resuscitated and stabilized to the medical officer's best ability. Transfer to a higher level of care should be considered on an individual basis, based on the severity of the incident and the facilities available, with the patient's best interests in mind. Patients with a documented cold injury should be referred to a higher level of care for consultation before being returned to full duty.

References

1. Environmental Emergencies, Charles E. Stewart, Williams and Wilkins 1990.
2. Clinical Practice of Emergency Medicine 2^nd edition, Ann L. Harwood-Nuss, Lippincott-Raven 1996.
3. Emergency Medicine: A Comprehensive Study Guide 4^th edition, Judith E. Tintinalli, McGraw-Hill Inc. 1996.
4. Emergency Medicine Concepts and Clinical Practice 4^th edition, Rosen / Barkin , Mosby 1998.