Hypothermia

Question 1

Definition of hypothermia

Answer 1

• Core temperature <35^oC

Question 2

Pathophysiology of hypothermia - how body heat is lost (4 mechanisms)

Answer 2

• Radiation (60%)
  
  • Infra-red emissions
• Conduction
  
  • Direct contact (15%)
  • 1^o means in cold water immersion
• Convection (15%)
  
  • Removes warmed air from around the body
  • Increased in windy environments
• Evaporation (10%)
  
  • Removel of warmed air
  • Increased in dry, windy environments

Question 3

Aetiology of hypothermia

Answer 3

• Primary - environmental exposure
• Secondary - change in temperatureset-point (i.e. age-related, hypothyroidism, autonomic neuropathy)

Question 4

Presentation of hypothermia

Answer 4

• Mild (32.2-35^oC)
  
  • Shivering
  • Tachycardia
  • Vasoconstriction
  • Apathy
• Moderate (28-32.2^oC)
  
  • Dysrhythmia, bradycardia, hypotension
  • J waves
  • ↓ reflexes, dilated pupils, ↓GCS
• Severe <28^oC
  
  • VT -> VF -> cardiogenic shock
  • Apnoea
  • Non-reactive pupils
  • Coagulopathy
  • Oliguria
  • Pulmonary oedema

Question 5

Investigations of hypothermia

Answer 5

• Rectal/ear temperature
• FBC, U&Es, glucose
• TFTs, blood gas
• ECG (J waves - between QRS and T wave, arrhythmas)

Question 6

Management of hypothermia

Answer 6

• Cardiac monitoring
• Warm IV fluids (0.9% NaCl)
• Urinary catheter
• Consider antibiotics for prevention of pneumonia (routine if temp <32 and >65 years)
• Slowly rewarm
  
  • Rewarming too quickly - peripheral vasodilation and shock
  • Aim for 0.5^oC/hr
  • Passive external - blankets, warm drinks
  • Active extermal - warm water, warmed air
  • Active internal - mediastinal lavage and CPB (severe hypothermia only)

Question 7

Complications of hypothermia

Answer 7

• Arrhythmias
• Pneumonia
• Coagulopathy
• Acute renal failure