What are the causes of hypothermia?

Causes of Hypothermia

Hypothermia occurs when core body temperature drops below 35°C and can be caused by various environmental, physiological, and medical factors that lead to excessive heat loss or inadequate heat production. 1, 2

Environmental Causes

• Exposure to cold environments - The primary cause of hypothermia is exposure to cold weather conditions, especially when combined with inadequate clothing or shelter 1, 2
• Cold water immersion - Immersion in cold water accelerates heat loss through conduction at a rate 25 times faster than air at the same temperature 2, 3
• Wet clothing - Moisture significantly increases heat loss through evaporation and conduction, with wet clothing being a major risk factor (OR 0.40 for presence of clothing as protective) 1
• Wind exposure - Increases convective heat loss and can dramatically lower the effective temperature (wind chill factor) 2

Trauma-Related Causes

• Severe injury - Blood loss, large open wounds, and significant trauma disrupt temperature regulation and are strongly associated with hypothermia 1
• Cold fluid resuscitation - Administration of unwarmed intravenous fluids can rapidly decrease core temperature, with infusion fluid temperature being a significant risk factor (OR 1.17) 1
• Prolonged immobilization - Especially on cold surfaces, leading to conductive heat loss 1
• Hemorrhagic shock - Reduces tissue perfusion and metabolic heat production 1

Medical and Physiological Causes

• Impaired thermoregulation - Conditions affecting the hypothalamus or autonomic nervous system 2, 4
• Endocrine disorders - Hypothyroidism, hypopituitarism, hypoadrenalism, and hypoglycemia reduce metabolic heat production 1, 4
• Age extremes - Very young and elderly individuals have reduced thermoregulatory capacity, with advanced age being a significant risk factor for poor rewarming 1, 2
• Malnutrition - Reduces metabolic rate and subcutaneous fat insulation 2
• Spinal cord injuries - Disrupt autonomic control of vasomotor tone and shivering 1

Medication and Substance-Related Causes

• Alcohol and drug intoxication - Causes vasodilation, impairs judgment, and suppresses shivering response 5, 1
• Sedatives and anesthetics - Suppress metabolic rate and impair thermoregulation, with anesthesia induction typically causing a temperature decrease of 1.6 ± 0.3°C in the first hour 1
• Vasodilators - Increase peripheral blood flow and heat loss 4
• Certain antipsychotics and antidepressants - Can disrupt hypothalamic temperature regulation 1

Hospital and Procedural Causes

• Prolonged surgical exposure - Open body cavities and extended procedures increase heat loss 1
• Cold operating rooms - Low ambient temperature in treatment areas (trauma bays, operating rooms) accelerates heat loss 6
• Mechanical ventilation with unwarmed gases - Increases respiratory heat loss 1

Social and Behavioral Factors

• Homelessness - Lack of adequate shelter during cold weather 1, 5
• Mental illness - Can impair judgment and self-care abilities 5
• Social isolation - Reduces likelihood of assistance during cold exposure 5
• Inadequate clothing - Insufficient insulation for environmental conditions 1

Severity Classification

Hypothermia severity is classified based on core temperature 1, 6:

• Cold stress: 35-37°C - Alert, possibly shivering
• Mild hypothermia: 32-35°C - Altered responsiveness, shivering
• Moderate hypothermia: 28-32°C - Decreased responsiveness, ±shivering
• Severe hypothermia: <28°C - Unresponsive, may appear lifeless
• Profound hypothermia: <24°C - Cessation of shivering, slow heart rate and breathing

Clinical Implications

• Hypothermia significantly increases mortality in trauma patients, with rates of 7% in normothermic versus 43% in hypothermic patients 6
• Hypothermia forms part of the "lethal triad" along with acidosis and coagulopathy, creating a synergistic effect that worsens outcomes 1
• Even mild hypothermia (32-35°C) impairs platelet function and can contribute to bleeding complications 1
• Severe hypothermia (<32°C) significantly affects clotting factor activity and fibrinogen synthesis 1

Understanding these causes is essential for prevention and early intervention, as hypothermia-related mortality remains significant with approximately 1,300 deaths annually in the United States 5.