Definition
Hypothermia is a medical condition characterized by a core body temperature that falls below the normal range required for spontaneous physiological functioning, typically defined as a temperature of less than 35 °C (95 °F) in humans.
Overview
Hypothermia occurs when heat loss exceeds heat production, leading to a gradual decline in core temperature. It can result from prolonged exposure to cold environments, immersion in cold water, inadequate clothing, certain medical conditions, or the use of substances that impair thermoregulation (e.g., alcohol, sedatives). Clinical presentation varies with severity and may progress rapidly, especially in vulnerable populations such as the elderly, infants, and individuals with chronic illnesses. Management focuses on rewarming, supportive care, and treatment of underlying causes.
Etymology/Origin
The term derives from the Greek prefix hypo- meaning “under” or “below,” and therme (θέρμη) meaning “heat.” It entered the English language in the early 19th century via medical literature.
Characteristics
| Aspect | Details |
|---|---|
| Classification by core temperature | • Mild: 32–35 °C (90–95 °F) – shivering, peripheral vasoconstriction, mental alertness may be preserved. • Moderate: 28–32 °C (82–90 °F) – reduced shivering, confusion, slurred speech, impaired coordination. • Severe: <28 °C (<82 °F) – absent shivering, profound CNS depression, bradycardia, hypotension, possible arrhythmias, risk of cardiac arrest. |
| Physiological signs | Vasoconstriction of peripheral vessels, decreased metabolic rate, reduced oxygen consumption, altered acid‑base balance, potential coagulopathy. |
| Common symptoms | Shivering (initially), cold skin, numbness, fatigue, confusion, drowsiness, slowed heart rate, respiratory depression. |
| Diagnostic criteria | Core temperature measurement (rectal, esophageal, or tympanic probe) <35 °C; clinical assessment of mental status and cardiovascular function. |
| Treatment modalities | • Passive external rewarming – blankets, insulated environment. • Active external rewarming – forced‑air warming blankets, heating pads (avoid direct skin contact to prevent burns). • Active core rewarming – warmed intravenous fluids, humidified oxygen, peritoneal or thoracic lavage, extracorporeal blood warming (e.g., cardiopulmonary bypass) for severe cases. • Supportive care – airway management, oxygenation, monitoring for arrhythmias, correction of electrolyte imbalances. |
| Complications | Cardiac arrhythmias (including ventricular fibrillation), myocardial ischemia, coagulopathy, renal failure, cerebral edema, and death if not promptly treated. |
Related Topics
- Thermoregulation – physiological mechanisms maintaining body temperature.
- Frostbite – localized tissue freezing injury often co‑occurring with hypothermia.
- Hyperthermia – condition of elevated core temperature.
- Cold‑water immersion – a high‑risk scenario for rapid heat loss.
- Shivering thermogenesis – muscle activity generating heat during mild hypothermia.
- Accidental hypothermia – non‑intentional exposure leading to temperature decline.
- Therapeutic hypothermia – controlled lowering of body temperature for medical interventions, such as post‑cardiac arrest neuroprotection.
This entry reflects current consensus in medical literature up to 2024.