Hypothermia

1.     They're not dead until they're warm and dead. Significant depression of vital signs and mental status occur, so do not delay resuscitation if patient appears dead.

2.     Risk factors for hypothermia:

  • Extremes of age: infants have greater body surface area relative to mass; elderly have lower metabolic rate and poor temperature sensation
  • Submersion in cold water: rapid thermal conduction in water
  • Alcohol ingestion: vasodilation, impaired shivering and awareness, hypothalamic dysfunction
  • Sepsis: 39% of consecutive patients with hypothermia studied at San Francisco General Hospital were bacteremic
  • Endocrine disorders: hypothyroidism, hypopituitarism, hypoadrenalism, diabetes, hypoglycemia
  • Head injury: central core temperature dysregulation
  • Drug ingestions (especially phenothiazines and barbiturates)

3.     Classification:

  • Mild (T 34-36):
    • Initial increase in metabolic rate and shivering.
    • Increased HR, BP, cardiac output, respiratory rate.
    • Impaired judgment, mild lethargy, confusion, loss of fine motor coordination.
  • Moderate (T 30-33.9):
    • Pupillary dilation, severe lethargy and confusion.
    • Decrease in BP and HR, cessation of cardiovascular activity.
    • Atrial fibrillation and other arrhythmias common.
  • Severe (T < 30):
    • Progressive bradycardia and hypotension, decreased respirations.
    • Muscle rigidity, loss of consciousness, absent DTRs or brainstem reflexes.
    • Cardiac irritability with high risk of VF or asystole.

4.     General principles:

  • Obtain accurate core temperature. Gold standard is esophageal probe but rectal probe is acceptable. Tympanic temperatures should be noted with suspicion.
  • Perform secondary survey to check for trauma and to remove wet clothing.
  • Patients should be on continuous monitoring and telemetry since hypothermic hearts are irritable. Do not handle roughly as patients can develop VF/VT. In fact, the use of an esophageal temperature probe and/or nasogastric lavage can precipitate VF/VT.
  • Look for the J wave (Osborne wave) on ECG?second upward wave immediately following the S wave. Seen best in V3 or V4 but classically in II, present in 80% of hypothermic patients, increases in size with more severe hypothermia.
  • Rapid core rewarming is key. Do not warm the extremities because this will cause peripheral vasodilation and return of cold blood to core. Use warmed IV fluid, warm humidified O2, heat lamps, hot water bottles or pack, peritoneal lavage, and extracorporeal rewarming (dialysis).
  • Patients tend to be dehydrated due to hypothermic diuresis.  Therefore, give warmed IV fluids empirically unless contraindicated.
  • Severely hypothermic hearts (T <30) have poor response to cardioactive stimuli, especially those used in ACLS (lidocaine, epinephrine, procainamide, pacer stimulation, defibrillation). Avoid multiple dosing of meds leading to toxic levels. Remember, rewarming is the solution.