Hypothermia

• Unintentional hypothermia (core cooling <35°C) is associated with significant morbidity and mortality. Roughly 1500 persons die of accidental hypothermia in the US annually.[1]
• Despite the high mortality associated with pre-hospital arrest, well-directed treatment can result in complete neurologic recovery in the hypothermic patient.[2]
• 50% who die of hypothermia are >65 years old[3]
• Risk of cardiac arrest increased with temperature <32°C, as stable cardiac rhythms can quickly degenerate into unstable rhythms. Hypothermic patient without a pulse must be managed differently due to physiology changes that occur at low temperatures. Defibrillation and many medications may be ineffective until the core temperature is above 30.0°C. If defibrillation is warranted but unsuccessful, active rewarming should be initiated while CPR is continued.

• Increased heat loss
  • Environmental exposure
    • Avalanche victims
    • Homeless population
    • Elderly patients → particularly low income during winter months
    • Submersion injuries
  • Induced vasodilation
    • Drugs
    • Carbon monoxide
    • Alcohol intoxication
• Decreased heat production
  • Endocrine
    • Hypopituitarism
    • Hypothyroidism
    • Hypoadrenalism
    • Hypoglycemia
  • Neuromuscular inefficiency
    • Extremes of age
    • Impaired shivering
  • Erythrodermas
    • Psoriasis
    • Exfoliative dermatitis
    • Ichthyosis
    • Eczema
    • Burns
  • Impaired Thermoregulation
  • Other
    • Sepsis
    • Trauma

• Generalized
  • Hypothermia
• Freezing
  • Frostbite
• Non-freezing
  • Trench foot
  • Chilblains (Pernio)
  • Cold panniculitis
  • Cold urticaria
  • Polar thigh

Atrial fibrillation and Osborn J waves in a person with hypothermia.

• Typical sequence is sinus bradycardia → atrial fibrillation with slow ventricular response → ventricular fibrillation → asystole
• Other ECG findings:
  • Osborn (J) wave - Size of wave correlates with degree of hypothermia. No prognostic value.
  • Muscle tremor artifact
  • T-wave inversions
  • PR, QRS, QT prolongation
  • ST segment elevation or depression
  • AV block
  • PVCs

• Handle patient gently
• V-fib may be induced by rough handling of patient due to irritable myocardium (anecdotal)

• Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
• Intubation
• Intubate gently
• if RSI is given medications may act at a slower rate

• Patients are also hypovolemic since hypothermia causes impaired renal concentrating ability, in turn causing cold diuresis
• Patients are prone to rhabdomyolysis and will need hydration
• Intravascular volume is lost due to extravascular shift
• NS preferred over LR as cold liver poorly metabolizes LR

• Only perform if patient truly does not have a pulse (unnecessary CPR may lead to V-fib)
• Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR

• May occur spontaneously if temperature <30°C (86°F)
• Rewarming is treatment of choice
• Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
• Activity of antiarrhythmics is unpredictable in hypothermia
• Hypothermic heart is relatively resistant to atropine, pacing, and countershock
• Ventricular tachycardia or Ventricular fibrillation are most common
  • May be refractory to therapy until patient is rewarmed
  • Attempt defibrillation
  • Value of deferring repeat defibrillation until a target temperature is reached is uncertain[5]
  • Reasonable to perform further defibrillation attempts concurrent with rewarming[5]

• Give if suspect sepsis (e.g. hypothermia fails to correct with rewarming measures)

• Consider if Wernicke disease is possible cause of hypothermia (e.g. alcoholic patient)

• Consider if patient has history of adrenal suppression or insufficiency
  • 100mg Hydrocortisone

• Consider if any suspicion for hypothyroidism/myxedema coma
• Could cause dysrhythmia or cardiac ischemia if not in myxedema coma

• Hyperglycemia common in hypothermia:
  • Stimulates catecholamine induced glycogenolysis
  • Inhibits insulin release and uptake by cell membranes
• Rebound hypoglycemia during rewarming can occur if clinicians too aggressively deliver exogenous insulin

• Prevent additional losses → remove wet clothes
• Heated room
• Blankets - If patient still shivering, capable of rewarming 0.5°C/hr

• Rewarm trunk BEFORE the extremities, otherwise you cause further hypotension ("core temperature afterdrop")
  • Afterdrop: warmed vasodilated peripheral tissue allows cooler blood in extremities to circulate back to core
• Options:
  • Warm water immersion (Capable of 2-4°C/Hr rewarming)
  • Heating blankets
  • Radiant heat
  • Forced air - e.g. Bair hugger (Up to 1-2.5°C/Hr rewarming)
  • Warm humidified air via facemask or endotracheal tube

Options:

• Heated IV fluids: 38-42°C.
  • Two animal studies have showed 65°C IVF via central line warmed subjects faster without side effects, but this has not been tested in humans[6][7]
  • If central line is placed, avoid irritating the heart
• GI tract lavage
  • Can cause fluid and electrolyte fluctuations, also risk of pulmonary aspiration
• Bladder lavage
  • Small surface area available for heat exchange
• Thoracic lavage
• Peritoneal lavage
• Bypass/ECMO[8]/AV Dialysis

• Should be considered if:
  • K > 12 mmol[10][11]
  • Asystole persists beyond >32°C
• Lactate and pH have less consistent prognostic significance in hypothermia