Hypothermia

Overview

Hypothermia occurs when the body's core temperature falls below 95°F (35°C), disrupting normal physiological functions. The human body normally maintains a temperature around 98.6°F (37°C) through various thermoregulatory mechanisms. When these mechanisms are overwhelmed by cold exposure or impaired by medical conditions, hypothermia can develop.

The condition is classified into three stages based on core body temperature: mild (90-95°F/32-35°C), moderate (82-90°F/28-32°C), and severe (below 82°F/28°C). Each stage presents with progressively more serious symptoms and complications. Even mild hypothermia can be dangerous, particularly in vulnerable populations such as the elderly, infants, and those with underlying medical conditions.

Hypothermia can occur not only in extreme cold weather but also in relatively mild conditions, especially when combined with wetness, wind, or prolonged exposure. Indoor hypothermia is also possible, particularly in elderly individuals or those with certain medical conditions. Understanding the risk factors and early recognition of symptoms are crucial for prevention and timely treatment.

Symptoms

The symptoms of hypothermia progress through stages as body temperature drops. Early recognition is critical, as the person may not realize they are in danger due to impaired mental function.

Primary Symptoms

• Depressive or psychotic symptoms - confusion, disorientation, hallucinations
• Emotional symptoms - irritability, mood changes, apathy
• Fainting - loss of consciousness due to circulatory changes
• Weakness - progressive loss of muscle strength and coordination

Mild Hypothermia (90-95°F/32-35°C)

• Shivering: Intense, uncontrollable shivering
• Cold skin: Pale, cold skin especially on extremities
• Clumsiness: Loss of fine motor control
• Fatigue: Increased tiredness and lethargy
• Increased heart rate: Body attempting to generate heat
• Increased breathing rate: Hyperventilation
• Mild confusion: Difficulty concentrating

Moderate Hypothermia (82-90°F/28-32°C)

• Violent shivering stops: Body can no longer generate heat
• Muscle stiffness: Progressive muscle rigidity
• Slurred speech: Difficulty speaking clearly
• Significant confusion: Impaired judgment and decision-making
• Stumbling: Loss of coordination and balance
• Slow, shallow breathing: Respiratory depression
• Decreased heart rate: Bradycardia

Severe Hypothermia (Below 82°F/28°C)

• Loss of consciousness: Coma-like state
• Cardiac arrhythmias: Irregular heart rhythms
• Barely detectable pulse: Extremely slow heart rate
• Minimal breathing: Respiratory rate may be 1-2 breaths per minute
• Dilated pupils: Pupils may not respond to light
• Paradoxical undressing: Removing clothes despite cold
• Terminal burrowing: Seeking small, enclosed spaces

Special Considerations

Infants and Children

• Bright red, cold skin
• Very low energy and lethargy
• Weak cry in infants
• Difficulty feeding

Elderly Adults

• Subtle symptoms that may be mistaken for other conditions
• Gradual onset over hours or days
• Increased fall risk
• Medication effects may mask symptoms

Causes

Hypothermia occurs when heat loss exceeds heat production. Understanding the various mechanisms that can lead to this condition helps in both prevention and treatment planning.

Environmental Causes

Cold Air Exposure

• Extreme cold weather: Temperatures below 50°F (10°C)
• Wind chill factor: Wind increases heat loss
• Inadequate clothing: Insufficient insulation
• Prolonged exposure: Extended time in cold conditions

Water-Related Hypothermia

• Cold water immersion: Water temperatures below 70°F (21°C)
• Wet clothing: Increased heat loss through evaporation
• Rain and snow: Moisture accelerates cooling
• Drowning incidents: Combined cold and water exposure

Medical Causes

Endocrine Disorders

• Hypothyroidism: Reduced metabolic heat production
• Hypoadrenalism: Impaired stress response
• Diabetes: Complications affecting circulation
• Hypopituitarism: Multiple hormone deficiencies

Neurological Conditions

• Stroke: Impaired thermoregulation
• Spinal cord injury: Loss of autonomic control
• Parkinson's disease: Reduced heat production
• Dementia: Impaired behavioral thermoregulation

Substance-Related Causes

• Alcohol intoxication: Vasodilation and impaired judgment
• Drug overdose: Various medications affecting thermoregulation
• Sedatives: Reduced awareness and heat production
• Anesthesia: Surgical and procedural cooling

Other Contributing Factors

• Malnutrition: Reduced energy for heat production
• Dehydration: Impaired circulation
• Burns: Loss of skin's insulation properties
• Sepsis: Overwhelming infection affecting temperature control
• Shock: Circulatory failure reducing heat distribution

Risk Factors

Certain individuals are at higher risk for developing hypothermia due to age, medical conditions, medications, or lifestyle factors.

Age-Related Risk Factors

Infants and Young Children

• Large surface area to body mass ratio: Rapid heat loss
• Limited ability to generate heat: Less muscle mass
• Inability to recognize danger: Cannot seek warmth independently
• Thinner skin: Less insulation

Elderly Adults (65+)

• Decreased metabolism: Reduced heat production
• Reduced subcutaneous fat: Less insulation
• Medication effects: Various drugs affecting thermoregulation
• Chronic diseases: Conditions impairing temperature control
• Social isolation: Delayed recognition and treatment

Medical Risk Factors

• Mental illness: Impaired judgment and awareness
• Dementia: Inability to recognize cold or seek warmth
• Cardiovascular disease: Poor circulation
• Diabetes: Complications affecting blood flow
• Arthritis: Limited mobility and ability to warm up
• Thyroid disorders: Altered metabolism

Lifestyle and Behavioral Factors

• Alcohol abuse: Impaired judgment and vasodilation
• Drug use: Altered mental state and thermoregulation
• Homelessness: Prolonged cold exposure
• Outdoor workers: Occupational cold exposure
• Athletes: Outdoor sports in cold weather

Medication-Related Risk Factors

• Sedatives: Reduced awareness and heat production
• Antipsychotics: Impaired thermoregulation
• Beta-blockers: Reduced cardiovascular response
• Muscle relaxants: Decreased heat generation

Environmental Risk Factors

• Inadequate heating: Poor home heating systems
• Insufficient clothing: Inappropriate dress for conditions
• Wet conditions: Increased heat loss
• High altitude: Increased cold exposure risk

Diagnosis

Diagnosing hypothermia requires accurate core body temperature measurement and assessment of associated symptoms. In emergency situations, treatment often begins before complete diagnostic workup.

Core Temperature Measurement

Preferred Methods

• Esophageal temperature: Most accurate for core temperature
• Rectal temperature: Commonly used, accurate for core measurement
• Bladder temperature: Reliable if urinary catheter in place
• Tympanic temperature: Less reliable in severe hypothermia

Temperature Classifications

• Mild hypothermia: 90-95°F (32-35°C)
• Moderate hypothermia: 82-90°F (28-32°C)
• Severe hypothermia: Below 82°F (28°C)

Clinical Assessment

History Taking

• Environmental exposure: Duration and conditions
• Clothing and protection: Adequacy of insulation
• Medical history: Predisposing conditions
• Medications: Drugs affecting thermoregulation
• Substance use: Alcohol or drug involvement

Physical Examination

• Vital signs: Heart rate, blood pressure, respiratory rate
• Neurological status: Level of consciousness, reflexes
• Skin examination: Color, temperature, signs of frostbite
• Cardiac assessment: Rhythm, murmurs, peripheral pulses

Laboratory Tests

• Complete blood count: Rule out infection or blood loss
• Comprehensive metabolic panel: Electrolyte abnormalities
• Blood gas analysis: Acid-base status and oxygenation
• Glucose level: Rule out hypoglycemia
• Thyroid function: If hypothyroidism suspected
• Toxicology screen: If substance use suspected

Imaging Studies

• Chest X-ray: Assess for pneumonia or pulmonary edema
• ECG: Monitor for cardiac arrhythmias
• CT scan: If head trauma or altered mental status

Monitoring

• Continuous temperature monitoring: Track rewarming progress
• Cardiac monitoring: Watch for arrhythmias during rewarming
• Neurological checks: Assess mental status changes
• Urine output: Monitor kidney function

Treatment Options

Treatment of hypothermia focuses on rewarming the body while supporting vital functions. The approach varies based on the severity of hypothermia and the patient's condition.

Emergency Response

Pre-Hospital Care

• Call emergency services: Activate EMS immediately
• Move to warm environment: Remove from cold exposure
• Handle gently: Avoid jarring movements that can trigger arrhythmias
• Remove wet clothing: Replace with dry, insulating materials
• Insulate the person: Cover with blankets, focus on core

Rewarming Strategies

Passive External Rewarming

• Indications: Mild hypothermia in otherwise healthy patients
• Methods: Warm environment, dry clothing, blankets
• Rate: 1-2°C per hour
• Monitoring: Continuous temperature and vital signs

Active External Rewarming

• Indications: Moderate hypothermia or failed passive rewarming
• Methods:
  • Forced air warming devices (Bair Hugger)
  • Warm water immersion (104-108°F/40-42°C)
  • Heating pads applied to trunk
• Rate: 1-4°C per hour
• Precautions: Avoid warming extremities first

Active Internal Rewarming

• Indications: Severe hypothermia, cardiovascular instability
• Methods:
  • Warm intravenous fluids (104°F/40°C)
  • Warm humidified oxygen
  • Peritoneal lavage with warm saline
  • Hemodialysis
  • Extracorporeal membrane oxygenation (ECMO)
  • Cardiopulmonary bypass
• Rate: 1-12°C per hour depending on method

Supportive Care

Cardiovascular Support

• Cardiac monitoring: Continuous ECG monitoring
• Gentle handling: Minimize manipulation to prevent arrhythmias
• Defibrillation: May be ineffective until core temperature >86°F (30°C)
• Medications: Most are ineffective until rewarmed

Respiratory Support

• Airway management: Intubation if necessary
• Mechanical ventilation: Heated and humidified gases
• Oxygen therapy: Warmed, humidified oxygen

Fluid and Electrolyte Management

• IV fluid resuscitation: Warm normal saline or lactated Ringer's
• Electrolyte monitoring: Potassium levels can fluctuate
• Glucose management: Monitor and treat hypoglycemia

Complications Management

• After-drop: Further temperature decrease during rewarming
• Rewarming shock: Vasodilation causing hypotension
• Compartment syndrome: From rewarming edema
• Rhabdomyolysis: Muscle breakdown from cold injury

What NOT to Do

• Do not give alcohol or caffeine
• Do not warm extremities first
• Do not massage or rub the skin vigorously
• Do not use direct heat sources on skin
• Do not assume the person is dead until warmed

Prevention

Preventing hypothermia involves preparation, awareness, and taking appropriate precautions when exposed to cold conditions.

Clothing and Gear

• Layer clothing: Multiple thin layers provide better insulation
• Stay dry: Waterproof outer layer, change wet clothes immediately
• Protect extremities: Insulated gloves, warm socks, waterproof boots
• Cover head and neck: Significant heat loss through these areas
• Appropriate materials: Wool or synthetic fabrics, avoid cotton

Environmental Precautions

• Check weather conditions: Plan for worst-case scenarios
• Limit time outdoors: Take frequent warm-up breaks
• Stay hydrated: Dehydration increases hypothermia risk
• Eat adequately: Body needs fuel to generate heat
• Avoid alcohol: Impairs judgment and increases heat loss

Home Safety

• Adequate heating: Maintain home temperature above 68°F (20°C)
• Heating system maintenance: Regular service and safety checks
• Emergency heating: Backup heat source if power fails
• Insulation: Proper home insulation and weatherproofing
• Carbon monoxide detectors: Prevent poisoning from heating devices

Special Population Considerations

Elderly Adults

• Regular wellness checks during cold weather
• Medication review for drugs affecting thermoregulation
• Social services support for adequate heating
• Emergency contact systems

Infants and Children

• Never leave children unattended in cold
• Appropriate clothing for outdoor activities
• Warm car before placing children inside
• Monitor for signs of cold stress

Outdoor Enthusiasts

• Proper training and preparation
• Emergency equipment and communication devices
• Travel with partners
• Know emergency procedures

High-Risk Situations

• Water activities: Wear life jackets, know rescue procedures
• Vehicle breakdown: Emergency kit with blankets and supplies
• Power outages: Alternative heating plans
• Outdoor work: Regular warm-up breaks, appropriate gear

When to See a Doctor

Call 911 immediately for:

• Any suspected hypothermia
• Confusion or altered mental state in cold conditions
• Loss of consciousness
• Severe shivering that suddenly stops
• Slurred speech or coordination problems
• Skin that is cold and blue or gray

Seek immediate medical attention for:

• Fainting or near-fainting episodes
• Progressive weakness in cold conditions
• Signs of frostbite (white or gray skin, skin that feels hard)
• Difficulty breathing or chest pain in cold

Consult healthcare provider for:

• Concerns about cold sensitivity
• Medication effects on temperature regulation
• Prevention strategies for high-risk individuals
• Home heating assistance programs

Related Conditions

• Frostbite
• Hypothyroidism
• Alcohol Intoxication
• Shock
• Sepsis
• Hypoglycemia

References

1. Zafren K, Giesbrecht GG, Danzl DF, et al. Wilderness Medical Associates practice guidelines for the out-of-hospital evaluation and treatment of accidental hypothermia. Wilderness Environ Med. 2014;25(4):425-445.
2. Brown DJ, Brugger H, Boyd J, et al. Accidental hypothermia. N Engl J Med. 2012;367(20):1930-1938.
3. Paal P, Gordon L, Strapazzon G, et al. Accidental hypothermia-an update. Scand J Trauma Resusc Emerg Med. 2016;24:111.
4. Centers for Disease Control and Prevention. Hypothermia-Related Deaths—United States, 1999–2002 and 2005. MMWR Morb Mortal Wkly Rep. 2006;55(10):282-284.
5. Dow J, Giesbrecht GG, Danzl DF, et al. Wilderness Medical Associates practice guidelines for the out-of-hospital evaluation and treatment of accidental hypothermia: 2019 update. Wilderness Environ Med. 2019;30(4S):S47-S69.