Hypothermia

Related Subjects: Acute Kidney Injury |Acute Rhabdomyolysis |Drowning |Hyperkalaemia |Hypothermia

“You’re not dead until you’re warm and dead.” This adage reminds clinicians to continue active resuscitation in severe hypothermia until core temperature normalizes. Younger or otherwise healthy individuals may have greater potential for survival, especially if their hypothermia developed rapidly (e.g., accidental immersion in cold water).

Definition & Classification

• Hypothermia: Unintentional fall in core body temperature below 35°C.
• Always measure core temperature with a low-reading thermometer (e.g., rectal, oesophageal probe).
• Degrees of Hypothermia:
  • Mild: 35–32°C
  • Moderate: 32–28°C
  • Severe: <28°C

Risk Factors

• Temperate climates have fewer cases; colder regions or winter sports enthusiasts face higher risk.
• Urban poor/homeless, individuals with alcohol/drug misuse, malnutrition, or poor socioeconomic conditions.
• Prolonged surgery or operating room exposure (cold environments, sedation).
• Occasionally attempted suicide by exposure to cold.
• Infants/children have underdeveloped thermoregulatory mechanisms and relatively larger surface area. Elderly are often at highest risk (poor mobility, reduced insulation, and chronic illness).

Hypothermia becomes critical when core temperature dips below 35°C. Infants and the elderly are particularly vulnerable due to inadequate thermoregulation and possible poor living conditions.

🩺 Clinical Features

• Mild (35–32°C): Shivering, seeking warmth, mild tachycardia, increasing desire for heat.
• Moderate (32–28°C): Possible confusion, ataxia, dehydration, diminished shivering reflex; bradycardia may develop.
• Severe (<28°C): Significant bradycardia, hypotension, cardiac dysrhythmias; risk of coma, absent pupillary reflexes, and ultimately asystole or ventricular fibrillation.
• Falls or strokes in a cold environment exacerbate hypothermia if the individual is immobilized. Always consider CT imaging if any suspicion of head injury or stroke.
• Check capillary blood glucose-hypoglycaemia may mimic or contribute to confusion and hypothermia.

Common Causes & Associations

• Environmental exposure (falls or immobilization in cold settings)
• Alcohol or sedatives (benzodiazepines, opiates) reducing shiver response and awareness
• Poverty, homelessness, lack of heating
• Endocrine/metabolic issues: Myxoedema coma (hypothyroidism), hypoglycaemia, adrenal insufficiency
• Potential co-factors: Carbon monoxide poisoning, attempted suicide, drowning, or electrocution

🔎 Investigations

• Blood Tests:
  • FBC: Elevated haematocrit (due to haemoconcentration), raised WCC (stress response)
  • U&E: Possible prerenal azotaemia, rhabdomyolysis (raised CK, K+, creatinine)
  • Blood Gases: Metabolic acidosis is common
  • Serum K+ abnormalities; monitor ECG closely
  • TFTs (TSH, T3/T4) if hypothyroidism is suspected
  • Cortisol levels if adrenal insufficiency is considered
  • Amylase may be raised (pancreatitis risk)
  • Toxicology screen if drug or alcohol misuse is suspected
  • COHb (carboxyhaemoglobin) for carbon monoxide poisoning
• ECG:
  • Bradycardia, first-degree AV block, prolonged QT interval
  • Atrial fibrillation or ventricular arrhythmias
  • Characteristic Osborne (J) waves, whose height correlates with degree of hypothermia
• Imaging:
  • Consider CT scan of the head in elderly or comatose patients (rule out stroke, head injury)
  • Chest X-ray or other imaging if pneumonia, trauma, or other pathologies are suspected

ECG and Osborne (J) Waves

The Osborne wave is a prominent deflection at the J point on the ECG. Its amplitude may be proportional to the severity of hypothermia.

Management (Seek Expert Help)

• Initial Stabilization (ABC):
  • Secure airway, provide high-flow O₂, establish IV access, apply telemetry for arrhythmia detection.
  • Avoid further heat loss-cover the patient after the primary survey.
• Rewarming Strategies:
  • Mild Hypothermia (32–35°C): Passive external rewarming (blankets, warm environment). Warm oral fluids if alert and stable.
  • Moderate/Severe Hypothermia (<32°C): Consider active internal rewarming-warmed IV fluids, warm humidified oxygen, gastric or peritoneal lavage with warmed fluids. In extreme cases, extracorporeal blood warming (bypass, ECMO) may be life-saving.
• Cardiac Arrest Protocol:
  • Continue resuscitation until core temperature is near normal; defibrillation may be less effective at very low temperatures, but do not abandon advanced life support prematurely.
• Additional Measures:
  • Monitor serum potassium, glucose, and acid-base status closely; correct hypoglycaemia as needed.
  • If there's suspicion of hypothyroidism or adrenal insufficiency, administer IV thyroxine (T3) and/or steroids (hydrocortisone).
  • Consider thiamine, naloxone, or dextrose if history suggests malnutrition, opioid use, or hypoglycaemia risk.

References

• Diagnosis and Treatment of Hypothermia (American Family Physician, 2004)

Cases - Hypothermia

• Case 1 - Environmental exposure ❄️: A 72-year-old homeless man is found outdoors in winter, drowsy and shivering. Core temperature 32°C. Exam: bradycardia, slurred speech, slow reflexes. ECG: J (Osborn) waves. Diagnosis: moderate hypothermia due to environmental exposure. Managed with warmed IV fluids, heated blankets, and gradual rewarming.
• Case 2 - Iatrogenic 🏥: A 64-year-old woman undergoing prolonged abdominal surgery develops intraoperative hypothermia (core temperature 34°C). Exam: cold peripheries, bradycardia. Blood gases: metabolic acidosis, coagulopathy. Diagnosis: perioperative hypothermia. Managed with forced-air warming devices and warmed IV fluids.
• Case 3 - Secondary to metabolic illness 🧬: A 55-year-old man with known hypothyroidism is brought in confused and hypothermic (30°C). Exam: bradycardia, hypotension, dry skin. TFTs: TSH very high, T4 low. Diagnosis: myxoedema coma with severe hypothermia. Managed with ICU admission, IV levothyroxine, hydrocortisone, and careful rewarming.

Teaching Point 🩺: Hypothermia is defined as core temperature <35°C. - Mild (32–35°C): shivering, tachycardia. - Moderate (28–32°C): bradycardia, confusion, hyporeflexia. - Severe (<28°C): coma, arrhythmias, cardiac arrest. Causes: environmental, iatrogenic, endocrine, sepsis, intoxication. Management = ABC resuscitation, passive/active rewarming, treat cause. Avoid rough handling in severe hypothermia → risk of VF.