Well, for us in the Northern Hemisphere, the weather has finally reminded us that it is December.  At times it seems as if going outside can be hazardous to your health.  This is particularly true if you are a kid.  While we have discussed Neonatal Hypothermia as a sign of possible serious bacterial infection or other metabolic conditions and we have touched on the topic of Hypothermia associated with toxins like Ethanol, most often hypothermia in kids is due to the laws of thermodynamics.

Hypothermia Basics

• Hypothermia is a significant public health issue – In the US, an average of 1,301 people die each year due to hypothermia.
• Hypothermia is defined as an unintentional drop in core body temperature <35 degrees Celsius.
• 3 Categories of Hypothermia:
  • Mild – Temp 35°C–32°C
  • Moderate – Temp 32°C–30°C
  • Severe – <30°C

   

• Most standard thermometers are not able to detect temperatures below 34.4°C. You need to use special glass or electronic thermometers.
• Cold stress potentially affects all organ systems!
  • Cardiovascular
    • Heart rate falls as temperature falls.
    • MAP and Cardiac Output also decline.
    • Atrial dysrhythmias commonly appear at temps <32°C, but are considered innocent, because ventricular response is slow.
    • Risk for ventricular fibrillation is greatest when temp 30°C.
  • Central Nervous System
    • At temp below 33°C, confusion, slurred speech, poor judgement, and ataxia are prevalent.
    • Cerebral metabolism decreases (which can be protective… to a point).
    • Cerebral perfusion is maintained until autoregulation fails at ~25°C.
  • Respiratory System
    • Initially, the cold stimulates respiratory drive.
    • As hypothermia continues, minute ventilation declines.
    • Bronchorrhea, due to local effect of cold air, can be severe enough to cause pulmonary edema.
  • Renal
    • The vasoconstriction in the extremities initially results in an increase in the blood volume “seen” by the kidneys.
    • This leads to a “Cold Diuresis” – kidneys produce a large amount of dilute urine.

   

Kids are more Susceptible to Hypothermia

• Age Matters!!
  • Newborns and infants
    • Dependent upon adults to be smart and protect them (not always the case).
    • Relatively large surface area to body mass leads to greater heat loss.
    • The newborn covered with amniotic fluid losses a tremendous amount of heat quickly.
    • Have a paucity of subcutaneous tissue to insulate them.
  • Toddlers and School-aged children
    • Become increasingly curious about their surroundings…
    • so are apt to get into trouble… but can’t get themselves out of trouble.
    • Submersion events in cold water accounts for most accidental hypothermia cases in older children.
    • Still have potential for greater heat loss than adults.
  • Teenagers
    • Have, what I consider, a relative “high testosterone to brain ratio” (at least in the teenage boys – who account for most of the environmental emergencies).
    • Have adult physiology, but more apt to place themselves in harms way purposefully without consideration of consequences.
    • Recently, there has been an increase in exposure-related hypothermia in older kids, likely due to popularity of winter sports.
    • Ethanol consumption complicates and exacerbates all of the processes of hypothermia.
    • Inexperience and lack of caution are a bad combination.

     

   

Initial Evaluation

• ABCDE’s — naturally.
  • Particularly focusing on getting all of the wet / cold clothing and materials off of them quickly.
• Start rewarming measures.
  • Simple Measures (Passive)
    • Cover the crown of head with warm blankets.
    • When ventilating, use heated and humidified oxygen.
    • Forced air-re-warming systems are also very helpful.
    • Warm IV fluids.
    • Hot packs/electric blankets can be dangerous as the vasoconstricted skin is susceptible to thermal injury.
  • More Advanced Measures (Active)
    • Used for moderate to severe hypothermia.
    • Irrigation of the Peritoneal cavity with heated fluid 40°C–45°C is effective.
    • ECMO!  Consider this early to help mobilize the resources.
• Know what the glucose level is!!
  • Don’t let hypoglycemia complicate the kid’s hypothermia!
  • Additionally, hyperglycemia may be present as insulin activity is impaired below 30°C.
• Consider Occult Trauma as the hypothermia may mask other clinical signs (like pain).
  • A low hemoglobin should spark concern for occult trauma.
  • Generally, hematocrit INCREASES by 2% for each 1°C drop in temperature.
• Consider coagulation studies (plts, coag studies, fibrinogen level) in the moderate and severe hypothermia cases.
  • Cold injury can lead to prolonged clotting times.
  • DIC can be seen after rewarming as well.
• Consider TOX screen – particularly for those adolescents.

Pulseless?

• Unfortunately, this may be the case with severe hypothermia.
• Focus on adequate chest compressions and appropriate ventilation.
• The cold myocardium may be resistant to defibrillation and to medications.
• Resist urge to keep giving medications – they won’t likely work and can build up in the system and cause more problems if you revive the patient.
• If initial defibrillation attempts do not work, chest compressions should be continued with minimal interruptions while measures to rewarm the patient are carried out.
• In general, resuscitation efforts should be continued until the patient is at least 30°C; however, there is NO consistently reliable prognostic laboratory value that can help guide the duration of the resuscitation.

References