What is considered a hypothermic temperature?

Definition of Hypothermia Based on Core Body Temperature

Hypothermia is defined as a core body temperature below 35°C (95°F). 1, 2

Classification of Hypothermia

Hypothermia is classified into different severity levels based on core temperature:

Classification	General Definition	Trauma Patient Definition
Mild hypothermia	35-32°C (95.0-89.6°F)	36-34°C (96.8-93.2°F)
Moderate hypothermia	32-28°C (89.6-82.4°F)	34-32°C (93.2-89.6°F)
Severe hypothermia	28-20°C (82.4-68.0°F)	<32°C (<89.6°F)
Profound hypothermia	20-14°C (68.0-57.2°F)	-

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Clinical Signs and Symptoms by Hypothermia Level

Understanding the clinical manifestations at different temperature thresholds is crucial for assessment and management:

Hypothermia Level	Core Temperature	Signs and Symptoms
Cold stress	35-37°C	Alert, possibly shivering
Mild hypothermia	32-35°C	Altered level of responsiveness, shivering
Moderate hypothermia	28-32°C	Decreased level of responsiveness, ±shivering
Severe hypothermia	<28°C	Unresponsive, may appear lifeless
Profound hypothermia	<24°C	Cessation of shivering, slow heart rate and breathing, high risk for irregular heart rhythm and cardiac arrest

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Special Considerations

• Trauma patients: The threshold for hypothermia is higher in trauma patients, with mild hypothermia starting at 36°C rather than 35°C 3
• Targeted temperature management (TTM): In post-cardiac arrest care, controlled hypothermia between 32-36°C may be therapeutic 4
• Risk factors: Certain populations are at higher risk for hypothermia:
  • Very young and elderly individuals
  • People with impaired temperature perception or regulation
  • Psychiatric patients taking certain medications (antipsychotics, beta-blockers, benzodiazepines) 5
  • Patients with seizure disorders, nocturnal enuresis, or mental retardation 5

Mechanisms of Heat Loss

Understanding the mechanisms of heat loss is important for prevention:

1. Radiation: Transfer of heat energy via electromagnetic waves (10-50 kcal/h)
2. Conduction: Transfer of energy between two solid objects in contact (16-30 kcal/h)
3. Convection: Transfer of heat energy during mass movement of gas or liquid (10-20 kcal/h)
4. Evaporation: Heat energy transferred during change of phase (12-16 kcal/h)

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Clinical Implications

• Hypothermia with decreased responsiveness (responding only to loud voice or pain) is a medical emergency 3
• In trauma patients, hypothermia can worsen coagulopathy and increase mortality 3, 4
• Accurate temperature measurement is crucial - oral, esophageal, or nasopharyngeal measurements are more accurate than axillary or rectal measurements 3

Prevention and Management

For patients with hypothermia:

• Protect from further heat loss by moving to a warm environment
• Remove wet clothing
• Allow passive rewarming with blankets
• Apply active rewarming if resources are available
• If unable to move to a warm environment, insulate from the ground and cover head and neck

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Hypothermia requires prompt recognition and management to prevent progression to more severe stages with associated cardiac instability and potential cardiac arrest.