Hypothermia

Aka: Hypothermia

1. See Also
   1. Hypothermia Management
   2. Hypothermia Management in the Wilderness
2. Definition
   1. Core temperature <95 F (35 C)
3. Epidemiology
   1. U.S. Deaths: 700 per year (50% are over age 65 years)
4. Risk Factors
   1. Extremes of age
   2. Alcohol intoxication
   3. Comorbid illness
5. Causes
   1. Environmental exposure
      1. Cold water immersion
      2. Exposure
   2. Sepsis
   3. Dermatitis
      1. Severe Burn Injury
      2. Severe skin exfoliation
      3. Severe Psoriasis
   4. Endocrinopathy
      1. Hypothyroidism
      2. Adrenal Insufficiency
   5. Substances
      1. Alcohol intoxication
      2. Phenothiazines
      3. Benzodiazepines or barbiturates
   6. Neurologic Disorder
      1. Acute Head Trauma or spinal cord transection
      2. Cerebrovascular Accident or Brain Tumor
      3. Wernicke's Encephalopathy
6. Mechanism
   1. Radiative heat loss (50% of heat loss)
      1. Majority of radiative Hair Loss via head (60%)
   2. Conductive heat loss (2-3% of heat loss)
      1. Wet clothing: Heat loss increases x5
      2. Cold water immersion: Heat loss increases x25
   3. Convective heat loss (10%)
      1. Important in windy conditions
      2. Convective loss increases with shivering
   4. Evaporative heat loss (Up to 27%)
   5. Respiratory heat loss (Up to 9%)
7. Signs: General
   1. Altered Mental Status
   2. Shivering
   3. Flushing
   4. Facial edema
   5. Initial Tachycardia progresses to Bradycardia
   6. Hypotension
   7. Paradoxical undressing
   8. Respiratory depression
   9. Ataxia
   10. Decreased Corneal reflex
8. Signs: Mild Hypothermia
   1. Core temperature: 95 to 90 F (35 to 32.2 C)
   2. Initial reaction to cold
      1. Shivering
      2. Increased Respiratory Rate, pulse and Blood Pressure
      3. Vasoconstriction
   3. Later with glycogen depletion and Fatigue
      1. Amnesia
      2. Ataxia
      3. Apathy
      4. Hypovolemia
      5. Cold diuresis
      6. Dysarthria
      7. Poor judgment
9. Signs: Moderate Hypothermia
   1. Core temperature: 90 to 82.4 F (34 to 28 C)
   2. Cardiac arrhythmia
      1. Atrial arrhythmia
      2. EKG with J Wave
   3. Altered Level of Consciousness to stupor
   4. Loss of reflexes
   5. Mydriasis
   6. Decreased Respiratory Rate, pulse and Blood Pressure
      1. Bradycardia: Heart Rate decreases by 50%
   7. Loss of voluntary control
10. Signs: Severe Hypothermia
    1. Core Temperature: < 82.4 degrees F (28 C)
    2. Major acid-base disturbance (Metabolic Acidosis)
    3. Pupils do not react and no Corneal reflex
    4. Apnea
    5. Coma
    6. Flat or decreased Electroencephalogram (EEG) activity
    7. Ventricular arrhythmias to Asystole
    8. Oliguria
11. Labs
    1. Bedside Glucose
       1. Hypoglycemia
    2. Chem8
       1. Acute Renal Failure
          1. Acute Tubular Necrosis due to Rhabdomyolysis
       2. Serum Potassium may change rapidly with rewarming
       3. Serum Glucose (see above)
    3. Creatine Phosphokinase (CPK)
    4. Arterial Blood Gas
    5. Coagulation studies
       1. Often normal despite cold-induced coagulopathy
12. Diagnostics: Electrocardiogram (EKG)
    1. General findings
       1. PR Prolongation
       2. QRS prolongation
       3. QT Prolongation
       4. J Waves
       5. Findings may mimic Acute Coronary Syndrome
    2. Dysrhythmias
       1. Atrial Fibrillation
       2. Ventricular Fibrillation
       3. Asystole
13. Management
    1. See Hypothermia Management
    2. See Hypothermia Management in the Wilderness
14. Complications
    1. Coagulopathy
       1. Usually resolves with rewarming
    2. Arrhythmia
15. Cardinal Rule
    1. Not dead until warm and dead unless already dead
       1. Patients have survived after low of 56 F (13 C)
    2. Do not cease Resuscitation until rewarmed
       1. Reevaluate after core temp >89.6 F (30 C)
16. References
    1. Danzl in Marx (2002) Rosen's Emergency Med, p. 1979-96
    2. Danzl in Auerbach (2001) Wilderness Med, p. 135-77
    3. McCullough (2004) Am Fam Physician 70:2325-32