[hypo- + therm- + -ia]
1. Core body temperature below the normal diurnal range due to failure of thermoregulation.
2. A core body temperature below 95°F (35°C). It may be further classified as mild (93.2°-96.8°F [34°-36°C]); moderate (86°-93°F [30°-34°C]); or severe (<86°F [30°C]). Hypothermia can be life-threatening, impairing neurological, cardiovascular, respiratory, and gastrointestinal systems.
Low body temperatures are most likely to affect newborns, older adults, the demented, those exposed to wet and cold conditions outdoors, alcoholics, septic patients, trauma patients, and patients with endocrine disorders such as severe hypothyroidism.
Phenothiazines and benzodiazepines may contribute to hypothermia by decreasing centrally mediated vasoconstriction; anesthetics may contribute by blocking shivering.
Hypothermia should be confirmed by temperature readings at two separate core locations, e.g., the esophagus and rectum.
To help prevent hypothermia, patients with multiple traumas receiving treatment in emergency facilities should be maintained under radiant warmers. Individuals who anticipate prolonged exposure to cold should be advised not to smoke or drink alcohol. They should wear layered clothing, two pairs of socks, mittens (not gloves), and a scarf or hat that covers their ears and head (to avoid loss of heat through the head). They also need adequate food and rest. If caught in severe cold weather, the individual should find warmth and shelter as soon as possible and increase physical activity to maintain body warmth.
Emergency department personnel first assess airway, breathing, and circulation. If breathing or pulse is not detected, cardiopulmonary resuscitation (CPR) begins immediately and continues until the patient's core body temperature reaches at least 89.6°F (32°C). Wet clothing should be removed and the patient protected against further heat loss. The patient is treated gently to avoid triggering cardiac dysrhythmias. If the patient has a core temperature of 93.2° to 96.8°F (34°-36°C) (mild hypothermia) and is breathing spontaneously, passive warming and active external warming are initiated. Passive warming involves covering the patient within dry insulating materials. Active external rewarming uses forced warm air, radiant heat sources, a fluid-circulating heat blanket, or heating pads to rewarm the body. If the patient's core temperature is 86° to 93°F (30°-34°C) (moderate hyperthermia), he or she is dried and covered, and external rewarming is begun immediately. If the patient's core temperature is less than 86°F (30°C) (severe hypothermia), invasive core rewarming is initiated, e.g., with infusions of warmed IV, gastric, and/or peritoneal fluids, warmed humidified oxygen, esophageal warming tubes, and extracorporeal hemodialysis.
Oral thermometers are likely to be inaccurate outdoors.
Hypothermia in newborns is prevented by maintaining the dry but unclothed infant under a radiant warmer with a thermistor probe until the temperature is stabilized. The initial bath is postponed until skin temperature stabilizes between 97.6° and 99°F (36.5°-37.2°C). Once stabilized, the infant's temperature is maintained by keeping him or her dry and wrapped in warm blankets, with the head covered, in a nursery unit with an ambient temperature of 75°F (24°C). If the infant has become hypothermic (cold delivery room, birth in a car on the way to the birth center, inadequate drying and wrapping after birth), rewarming is accomplished with great care over a period of 2 to 4 hr, as rapid warming or cooling may result in apneic spells or acidosis.
SYN: SEE: cold stress
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