What are the causes of hypothermia?

Causes of Hypothermia

Hypothermia occurs through four primary mechanisms of heat loss: conduction, convection, radiation, and evaporation, with risk factors including environmental exposure, age extremes, and impaired thermoregulation. 1

Primary Causes of Hypothermia

Environmental Causes

• Cold exposure - primary cause in otherwise healthy individuals 1
  • Prolonged exposure to cold environments
  • Immersion in cold water
  • Inadequate clothing for weather conditions
  • Wind exposure increasing heat loss through convection

High-Risk Populations

• Age-related factors 1
  • Very young (especially infants)
  • Elderly (highest death rates)
• Geographic factors
  • Rural areas have higher mortality rates 1
  • Men are at higher risk of death from hypothermia 1

Medical and Physiological Causes

• Impaired thermoregulation 1, 2

  • Endocrine disorders (hypothyroidism, hypoadrenalism)
  • Central nervous system dysfunction
  • Metabolic disorders

• Trauma-related causes 1

  • Major trauma with blood loss
  • Shock or persistent hypotension
  • Trauma-induced coagulopathy (associated with core temperature <35°C)

• Drug and toxin-related causes 1, 2

  • Alcohol intoxication
  • Sedatives and anesthetic agents
  • Barbiturates
  • Opioids
  • Antiepileptic medications

• Metabolic causes 2

  • Hypoglycemia
  • Electrolyte abnormalities
  • Malnutrition

Mechanisms of Heat Loss

1. Conduction - direct transfer of heat to a colder surface 1

   • Contact with cold ground, water, or objects

2. Convection - heat loss through movement of air or water 1, 3

   • Wind chill effect
   • Cold water immersion

3. Radiation - heat emitted from warm body to colder environment 1, 3

   • Uncovered head and extremities
   • Exposure to cold night sky

4. Evaporation - heat loss through conversion of water to vapor 1

   • Wet clothing
   • Sweating
   • Respiratory water loss

Classification of Hypothermia

Hypothermia is classified by core temperature and associated symptoms 1:

Classification	Temperature	Key Signs/Symptoms
Cold stress	35-37°C	Alert, possible shivering
Mild hypothermia	32-35°C	Altered mental status, shivering
Moderate hypothermia	28-32°C	Decreased responsiveness, ±shivering
Severe hypothermia	<28°C	Unresponsive, may appear lifeless
Profound hypothermia	<24°C	No shivering, slow heart rate/breathing, high risk of cardiac arrest

Clinical Implications

• Hypothermia significantly increases mortality in trauma patients 1
• Each 1°C drop in temperature causes approximately 10% drop in coagulation factor function 1
• Hypothermia in trauma patients leads to higher blood loss and transfusion requirements 1
• Core temperature <34°C is associated with >80% mortality risk in patients requiring massive transfusion 1

Prevention Strategies

• Proper clothing (clean, layered, and loose) 4
  • Moisture-wicking base layers
  • Wool or fleece middle layers
  • Moisture-repellent outer layers
• Insulation from ground surfaces 1
• Covering head and neck 1
• Protection from wind using plastic or foil layers 1
• Avoiding alcohol consumption in cold environments 2

Special Considerations

• Elderly patients may present with atypical symptoms 5
• Patients with altered mental status from any cause are at higher risk 2
• Medications affecting vasoconstriction or shivering can predispose to hypothermia 2
• Underlying medical conditions may mask or exacerbate hypothermia 2

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