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About Hypothermia
Case Scenario:
A 34-year Indian mountaineer who fell accidentally into an approx. 300m deep crevasse while descending down to base camp in Annapurna Mountain at around 5000m altitude was rescued after 3 days by a rescue team. The patient was immediately rescued to Manipal Hospital. During transport patient was ice cold and unresponsive to command. At arrival there was no spontaneous respiratory effort with asystole in ECG with patient very cold to touch. Immediately airway was secured with endotracheal intubation and cardiopulmonary resuscitation was started. Rewarming was done by conventional rewarming methods. The patient achieved return of spontaneous circulation (ROSC) after 4 hours of cardiopulmonary resuscitation. Read More...
Hypothermia Definition:
Accidental hypothermia occurs when there is an unintentional drop in the body’s core temperature below 35°C (95°F).
Primary Hypothermia → Direct exposure of previously healthy individual to the cold
Seconday Hypothermia → Hypothermia due to complications of serious systemic disorders/injury → Hypoglycemia, Hypovolemia, or toxin overdose → Higher Mortality
Risk Factors for Hypothermai:
Age Extremes
Enviromental Exposure
Drugs Overdose & Alcohol
Malnutrition
Endocrine (Hypoglycemia, Hypothyroidism, Adrenal Insufficiency)
Multisystemic (Trauma, Sepsis, Shock, Burn)
Mechanism of Heat Loss:
Radiation 55-65%
Conduction 10-15%
Convection
Evaporation
Respiration
Thermoregulation
Preoptic anterior hypothalamus → Immediate → Autonomic Nervous System → release of norepinephrine → Increased muscle tone, Shivering, thermogenesis , Increase BMR Endocrine System → Delayed Control (Thyroid axis) → Increase BMR
Grading Of Hypothermia :
Swiss Staging System for Hypothermia (35-32-28-24)
Diagnosis and Stabilization
Rectal Probe or Esophageal Probe used for diagnosis
Cardiac Monitoring → Ventricular Fribrillation
Pulse Oximetry ( tissue oxygenation is affected adversely)
BP Monitoring : Maintain MAP >60 mmHg
Pathophysiology:
Flowchart
Exposure to Cold Environment
↓
Heat Loss > Heat Production
↓
Drop in Core Body Temperature (<35°C)
↓
Impaired Thermoregulation (Hypothalamus Dysfunction)
↓
Multisystem Effects:
Central Nervous System:
- ↓ Cerebral metabolism
- ↓ Consciousness → Confusion → Stupor → Coma
Cardiovascular System:
- Initial tachycardia → Bradycardia
- ↓ Myocardial contractility
- ↑ Risk of arrhythmias (VF/VT)
- ↓ Cardiac output → Hypotension
Respiratory System:
- ↓ Respiratory rate → Hypoventilation → Apnea
Renal System:
- Cold diuresis → Dehydration
- ↓ Renal perfusion → Acute tubular necrosis
Hematologic System:
- Coagulopathy + Platelet dysfunction
- ↑ Blood viscosity → Thrombosis
- Risk of DIC
Metabolic Effects:
- Initial hyperglycemia → Later hypoglycemia
- Electrolyte imbalance (K+, Na+, Mg++)
- Metabolic + respiratory acidosis
↓
Shivering Ceases (~30–32°C)
↓
Rapid Temperature Decline
↓
Severe Hypothermia (<28°C)
↓
Ventricular Fibrillation / Asystole
↓
🕱 Death
Fun Facts
Patient in cardiac arrest due to hypothermia → Prolonged CPR needed → Survival has occurred with a cardiac arrest time over 7 h → Decision to terminate CPR past 33°C (91°F) should be predicated on the type and severity of the precipitants of hypothermia (Swiss Grading System)
Ethanol → vasodilation (which increases heat loss), reduces thermogenesis and gluconeogenesis, and may impair judgment/conciousness → more chance of hypothermia
Drug Overdose → Antipsychotics, antidepressants, anxiolytics, benzodiazepines → reduce centrally mediated vaso constriction → more chance of hypothermia
Paradoxical undressing
Flowchart
Severe Hypothermia (<28–30°C)
↓
CNS Dysfunction (Hypothalamus + Cortex)
↓
↓ Judgment, Confusion, Disorientation
↓
Loss of Vasoconstriction (Vasomotor Paralysis)
↓
Sudden Vasodilation → Sensation of Warmth
↓
False Feeling of Being Hot
↓
Victim Removes Clothing
↓
↑ Heat Loss → Rapid Temperature Drop
↓
Worsening Hypothermia
↓
Collapse/Death
Management:
Passive external rewarmingActive rewarming1. Covering and insulating the patient in a warm environment
2. Rate of rewarming is usually 0.5°–2°C (1.10°–4.4°F) per hour
3. Ideal for previously healthy patients who develop acute, mild primary accidental hypothermia1. Equipment : External heat Exchange Pads, Hot Packs
2. Application Core temperature <32°C (> Peripheral Heat application → Reduce risk of core temperature “after drop”
Prevention:
Primary Hypothermia : Prevent Extreme Cold Exposure and Application of passive external rewarming
Secondary Hypothermia : Treat Underlying secondary disease and application of passive external rewarming
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