What are the causes of hypothermia?

Causes of Hypothermia

Hypothermia occurs when heat loss from the body exceeds heat gain, causing the core body temperature to fall below 35°C, and is caused by environmental exposure, medical conditions, and iatrogenic factors that impair thermoregulation or increase heat loss. 1

Environmental Causes

• Cold exposure: Prolonged exposure to cold environments without adequate protective clothing 1, 2
• Immersion: Contact with cold water (immersion/trench foot) which accelerates heat loss through conduction 3
• Wind exposure: Increases convective heat loss (wind chill effect) 3
• Wet clothing: Significantly increases heat loss through evaporation and conduction 1
• Inadequate shelter: Homelessness or inadequate housing during cold weather 1

Physiological and Medical Causes

• Age-related factors:

  • Very young (especially infants) - underdeveloped thermoregulation 1
  • Elderly - impaired thermoregulation, decreased perception of cold 1, 4

• Endocrine disorders:

  • Hypothyroidism - reduced metabolic rate and heat production 5, 6
  • Adrenal insufficiency - impaired stress response and thermoregulation 5
  • Hypopituitarism - disruption of hormonal regulation 1

• Neurological conditions:

  • Hypothalamic dysfunction/lesions - disruption of temperature regulation center 5
  • Spinal cord injuries - impaired autonomic nervous system function 1
  • Wernicke encephalopathy - metabolic brain disorder affecting temperature regulation 5

• Metabolic disorders:

  • Hypoglycemia - insufficient glucose for heat production 1
  • Malnutrition - inadequate metabolic substrates for thermogenesis 5

Substance-Related Causes

• Alcohol consumption: Causes vasodilation, impairs shivering, and clouds judgment about cold exposure 2, 6
• Drug use:
  • Sedatives - decrease metabolic rate and impair thermoregulation 1
  • Phenothiazines - affect hypothalamic temperature regulation 6
  • Barbiturates - depress central nervous system function 6

Trauma and Critical Illness

• Trauma-induced factors:

  • Hemorrhage/shock - reduced tissue perfusion and metabolic activity 1
  • Open wounds/burns - increased heat loss through damaged skin 1
  • Head trauma - disruption of central temperature regulation 1

• Sepsis and infection: Dysregulation of thermoregulatory mechanisms 5, 6

Iatrogenic Causes

• Medical procedures:
  • Anesthesia - impairs thermoregulation and causes vasodilation 1
  • Surgery - exposure of body cavities, especially abdominal 1
  • Cold fluid infusion - direct cooling effect on core temperature 1
  • Mechanical ventilation with cold gases 1

Heat Loss Mechanisms

Heat loss occurs through four primary mechanisms 1:

1. Conduction: Direct transfer of heat to colder objects in contact with the body
2. Convection: Heat loss to moving air or water around the body
3. Radiation: Heat emission from the body surface to the environment
4. Evaporation: Heat loss through conversion of water to vapor (sweating, respiration)

High-Risk Populations

• Elderly individuals (especially >65 years) 1, 4
• Very young children and infants 1
• Homeless or socially isolated individuals 1
• Patients with severe trauma and blood loss 1
• Individuals with substance abuse disorders 2, 6
• Patients with altered mental status from any cause 2
• Individuals with endocrine disorders 5, 6

Clinical Implications

Hypothermia significantly increases mortality in trauma patients 1 and contributes to coagulopathy through:

• Impaired platelet function (33-37°C) 1
• Decreased clotting factor activity (below 33°C) 1
• Reduced fibrinogen synthesis 1
• Enzyme inhibition affecting the coagulation cascade 1

For each 1°C drop in temperature, there is approximately a 10% decrease in coagulation factor function 1.

Understanding these causes is essential for prevention, early recognition, and appropriate management of hypothermia, which can significantly reduce associated morbidity and mortality.