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Hypothermia

Hypothermia is defined as core temperature (measured by oesophageal, rectal or bladder probe) of < 35°C.

Predisposing factors

Increased loss:

  • exposure/entrapment
  • cold water immersion
  • vasodilation, such as by alcohol, drugs/medications and sepsis
  • Skin conditions, such as psoriasis, burns, erythoderma and TEN.

Decreased production:

  • Age – neonates, elderly
  • Endocrine failure – pituitary, thyroid or adrenal insufficiency
  • Nutritional deficiency – hypoglycaemia, anorexia, malnutrition
  • Inactivity, immobility
  • Muscle relaxants

CNS dysfunction:

  • Drugs – sedatives, alcohol, opioids
  • CNS – trauma, intracranial haemorrhage, neoplasm
  • Acidosis, anoxia or encephalopathy

Presentation

It can be further categorised:

  • Mild (35-32°C)

  • Moderate (32-28°C)

  • Severe (<28°C)

Mild hypothermia (32-35°C)

  • Associated with increased basal metabolic rate
  • Maximal shivering (for thermogenesis)
  • Amnesia, dysarthria, ataxia, apathy
  • Normal blood pressure.

Moderate hypothermia (28-32°C)

  • Progressive reduction in temperature results in stupor
  • Shivering stops
  • Atrial fibrillation and other dysrhythmias develop, cardiac output 2/3 of normal
  • Progressive loss of consciousness, pulse and respiration; pupils dilated at 29°C.

Severe hypothermia (< 28°C)

  • Loss of reflexes and progressive paralysis - reflexes absent at 26°C
  • Major acid base disturbance
  • Significant reduction in cerebral blood flow (1/3) and cardiac output (45%) at 25°C
  • Pulmonary oedema, significant hypotension and bradycardia develop
  • Maximum risk of VF at 22°C
  • Flat EEG at 19°C, asystole at 18°C

Investigations

Bedside:

  • Temperature measurement, rectal, oesophageal, bladder temperature probe
  • BSL
  • ECG

    • bradycardia, atrial fibrillation (AF)

    • prolonged PR, QRS and QT intervals

    • "J” or Osborne waves - “J” gets bigger the more severe the hypothermia

    • ST junction elevation due to delayed depolarisation with temp

Laboratory

  • FBC - WCC in sepsis
  • EUC, Hypo- or hyperkalaemia
  • Acute renal failure (high urea and creatinine)
  • BSL, Hypo- or hyperglycaemia
  • Clotting studies, Coagulopathy and DIC
  • Venous blood gases (VBG)
    • mild often shows a respiratory alkalosis
    • moderate to severe progresses to a mixed metabolic and respiratory acidosis

Management

  • Primary survey, ABCDE approach and immediate resuscitation in systems, including oxygen, IV analgesia and (warmed 42°C) fluids via x2 large bore cannulae
  • Measure pulse for 1 minute, commence CPR
  • Call for help early - senior ED
    • remove wet clothing, towels, blankets
    • gentle handling of patient (rough handling may precipitate cardiac dysrhythmias – probably overstated)
    • consider traumatic or medical causes for hypothermia
    • correct dehydration with warmed IV fluids
    • correct hypoglycaemia with IV dextrose
    • cover with warm blankets or heated air blankets (“Bair Hugger”)
    • temperature should increase in a warm room with the above measures (approx 2°C per hour)

Rewarming Techniques

Passive rewarming

  • Usually sufficient for mild hypothermia
  • Involves removal of wet clothing, keep patient in warm, dry environment with blankets

Active external rewarming

  • Indicated for moderate hypothermia
  • External application of heat via heated air blankets (“Bair hugger”) and radiant heat

Active internal rewarming

  • Warmed humidified oxygen at 40-45°C (if not available in the ED may be available in operating theatres or ICU)
  • Blood / fluid warmer for all IV infusions
  • Warm water lavage via
    • thoracic closed lavage (constant flow using 2 tubes possible), or left sided thoracotomy
    • urinary catheter
    • peritoneal
    • (nasogastric, rectal tube, less effective, more risk, use other places first)
  • Cardiopulmonary bypass (CPB) or ECMO if available has also been used for life-threatening cases (severe hypothermia)

If CPB not available pleural lavage can be used with warm water/saline

Cardiac Management Issues

Cardiac Dysrhythmias:

  • CPR for asystole and VF
  • VF may not be successfully electrically cardioverted until the temperature is >30°C
  • AF will revert spontaneously when the temperature returns towards normal, bradycardia is a normal physiological response to hypothermia and needs no treatment

Management - Cardiac Arrest:

  • Hypothermia is neuro (brain) protective
  • Don’t diagnose death in a cold patient - wait until they are “warm (>30°C) and dead”
  • CPR as standard 30:2 ratio
  • Active core rewarming techniques, used during CPR
  • Drugs and cardioversion unlikely to be effective until the temperature rises to >30°C
  • Double the time between drug doses during CPR at temps between 30°C and 35°C

Further Reference and Resources

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