Hypothermia, Accidental

Stages of Hypothermia

MILD HYPOTHERMIA

32.2-35°C (90-95°F)

Early Stage	Decompensated Stage
Hypertenstion	Apathy/Impaired Judgment
Tachycardia	Ataxia
Shivering	Cold diuresis-kidneys unable to concentrate urine
Vasoconstriction	Hypovolemia

MODERATE HYPOTHERMIA

28-32.2°C (82.4-90°F)

Clinical Findings
Atrial dysrhythmias
J wave on ECG
Hypotension, bradycardia
Lethargy
Mydriasis
Diminished gag reflex
Loss of shivering
Hyporeflexia

SEVERE HYPOTHERMIA

<28°C (<82.4°F)

Clinical Findings
Apnea
Coma
No activity on EEG
Fixed pupils
Oliguria
Pulmonary edema
Ventricular dysrhythmias
Asystole

Tip

• Many thermometers do not measure below 34.4°C (94°F). Need special low-tempsensing rectal or bladder thermometers.
• Avoid jostling the hypothermic patient too much because of myocardial irritability and consequent arrhythmias.

Direct complications from hypothermia and rewarming

• Rhabdomyolysis
• Acute tubular necrosis and renal failure
• Electrolyte shifts, especially K+ because of acid-base changes during rewarming
• Hypoglycemia from depleted glycogen stores
• Functional coagulapathy: May have normal coag studies because have to be rewarmed to run the assay

Rewarming approaches

1. Passive Rewarming: Remove cold, damp clothes. Wrap with blankets.

2. Active External Rewarming: Apply heat to skin

   • Heating blanket or radiant heat
   • Hot water bottles or heating pads to truncal surfaces. Caution-- do not burn skin.
   • Risk of “Core Temperature Afterdrop”, vasodilation with active external rewarming causes cold peripheral blood to return to heart. Give warm IV fluid beforehand.
   • Risk of “Rewarming Acidosis”. Lactate from periphery returns to core circulation. May cause transient shock during rewarming.

3. Active Core Rewarming

   • Humidified air, 40°C (104°F) – increases core temp by 1-2.5°C (1.8-4.5°F) per hr
   • Warm IV fluids at 40-45°C
   • Cardiopulmonary bypass or hemodialysis, Increases core temp by 1-2°C (1.8-3.6°F) every 3-5 minutes
   • Warm fluid lavage of stomach, colon, bladder, pleural space
   • Peritoneal dialysis. Normal saline at 40-45°C at 6-10 L/hr increases core temp by 1-3°C (1.8-5.4°F) per hour when combined with heated oxygen.
   • Mediastinal lavage via open thoracotomy

Choosing a rewarming approach

General approach

• Check glucose.
• Consider thiamine 100 mg IV, esp if chronic EtOH at risk for Wernicke’s
• Treat underlying etiology for hypothermia
• Give antibiotics +/- steroids, as appropriate

If patient in cardiopulmonary arrest

• Intubate, CPR, ACLS protocol
• Warm IVF
• Heated humidified oxygen
• Extracorporeal rewarming (i.e. cardiopulmonary bypass), if not immediately available, do active core rewarming measures
• Rewarm to target temperature >30°C (86°F)

If NOT in cardiopulmonary arrest AND temperature <32°C (89.6°F)

• Active External Rewarming (i.e. Bair Hugger, warm blankets), and
• Minimally invasive Active Core Rewarming (warm IVF, warm air)

If NOT in cardiopulmonary arrest AND temp ≥32°C (89.6°F)

• Passive external rewarming measures

References

• McCullough L, Arora S. Diagnosis and treatment of hypothermia. Am Fam Physician. 2004 Dec 15;70(12):2325-32. [PubMed]