Causes of Hypothermia
Hypothermia is primarily caused by exposure to cold environmental temperatures, with additional risk factors including advanced age, trauma severity, infusion of cold fluids, and various patient-specific conditions that impair thermoregulation. 1
Definition and Classification
Hypothermia occurs when core body temperature drops below 35°C (95°F). It can be classified by severity:
- Cold stress: 35-37°C - Alert, possibly shivering
- Mild hypothermia: 32-35°C - Altered mental status, shivering
- Moderate hypothermia: 28-32°C - Decreased responsiveness, with or without shivering
- Severe hypothermia: <28°C - Unresponsive, may appear lifeless
- Profound hypothermia: <24°C - Cessation of shivering, slow heart rate and breathing, high risk for cardiac arrest 1
Primary Mechanisms of Heat Loss
Heat loss occurs through four main mechanisms:
- Conduction: Direct transfer of heat to a colder object or surface in contact with the body
- Convection: Heat loss through air or water moving across the body surface
- Radiation: Heat emission from the body surface to the environment
- Evaporation: Heat loss through conversion of water to vapor (sweating, respiration) 1
Risk Factors for Hypothermia
Environmental Factors
- Cold ambient temperature
- Wind exposure (increases convective heat loss)
- Wet conditions (water conducts heat 25 times faster than air)
- Inadequate clothing or shelter 1
Patient-Specific Factors
- Advanced age: Reduced thermoregulatory capacity and impaired perception of cold 1
- Very young age: Immature thermoregulation
- Medical conditions:
- Hypothyroidism
- Hypopituitarism
- Hypoglycemia
- Spinal cord injury (impaired autonomic regulation)
- Malnutrition 1
- Substance use: Alcohol and drugs that impair judgment or thermoregulation 1
- Homelessness: Prolonged environmental exposure 1
Trauma-Related Factors
- Severity of injury: Higher injury severity scores correlate with hypothermia risk 1
- Blood loss: Reduces metabolic heat production
- Large open wounds: Increases heat loss
- Significant head injury: Disrupts central temperature regulation
- Hypotension: Systolic BP <100 mmHg increases risk 1
Medical Interventions
- Infusion of cold fluids: IV fluids below body temperature contribute significantly to hypothermia 1
- Anesthesia: Causes vasodilation and impairs thermoregulation, typically decreasing temperature by 1-1.6°C in the first hour 1
- Prolonged surgery: Extended exposure in cold operating rooms 1
- Ventilation with cold gases: Increases respiratory heat loss 1
Special Considerations
Trauma Patients
Hypothermia in trauma patients is particularly dangerous as it contributes to the "lethal triad" of:
- Hypothermia
- Acidosis
- Coagulopathy
This combination significantly increases mortality, with coagulation function decreasing approximately 10% for each 1°C drop in temperature 1.
Vulnerable Populations
In the United States, hypothermia causes approximately 1,300 deaths annually, with highest mortality rates among:
- Men
- Elderly individuals
- People in rural areas 1
Prevention Strategies
Prevention of hypothermia should focus on:
- Appropriate layered clothing
- Removing wet clothing promptly
- Insulation from cold surfaces
- Covering the head and neck (significant heat loss area)
- Using windproof outer layers
- Maintaining adequate caloric intake 1
In medical settings, prevention includes:
- Warming IV fluids
- Maintaining warm ambient temperatures
- Using warming devices during procedures
- Minimizing exposure during examinations and procedures 1
By understanding these causes and risk factors, healthcare providers can better identify patients at risk for hypothermia and implement appropriate preventive and treatment measures.