Accidental hypothermia

Background

Definition: Core Temp <35C (95F)

• 50% who die of hypothermia are >65 years old

Clinical Features

Swiss Hypothermia Staging System

Classification	Temperature	Signs/Symptoms
I / Mild	32-35°C (90-95°F)	Shivering, awake
II / Moderate	28-32°C (82-90°F)	Shivering, depressed mental status
III / Severe	20-28°C (68-82°F)	unconscious/severely depressed mental status, shivering ceases
IV / Profound	<20°C (68°F)	unobtainable VS

Differential Diagnosis

Impaired thermoregulation

• Central failure
  • Anorexia nervosa
  • CVA
  • Head trauma
  • Hypothalamic dysfunction
  • Metabolic failure
  • Neoplasm
  • Parkinson's disease
  • Drugs-Ethanol, Sedatives-hypnotics
  • SAH
  • Toxins
• Peripheral failure
  • Acute spinal cord transection
  • Decreased heat production
  • Neuropathy
• Endocrine
  • DKA or alcoholic ketoacidosis
  • Hypothyroidism
  • Hypoadrenalism
  • Hypopituitarism
  • Lactic acidosis (Sepsis)
• Insufficient energy
  • Extreme physical exertion
  • Hypoglycemia
  • Malnutrition
• Neuromuscular compromise
  • Recent birth or advanced age
  • Impaired shivering

Increased heat loss

• Dermatologic
  • Burns
  • Exfoliative dermatitis
• Iatrogenic
  • Massive fluid or blood resuscitation
  • Emergency childbirth
  • Heat stroke treatment
• Other
  • Carcinomatosis
  • Cardiopulmonary disease
  • Multisystem Trauma
  • Shock

Diagnosis

• Low-reading thermometer
  • Some standard thermometers record only to 34C

ECG

• Typical sequence is sinus brady > a fib with slow ventricular response > v-fib > asystole
• Other ECG findings:
  • Osborn (J) wave
  • T-wave inversions
  • PR, QRS, QT prolongation
  • Muscle tremor artifact
  • AV block
  • PVCs

Treatment

General

• Handle pt gently
  • V-fib may be induced by rough handling of pt due to irritable myocardium (anecdotal)
• O2
  • Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
• Intubation
  • same indications as normothermic patients
  • RSI medications may be ineffective at temperatures <30C
• IVF
  • Reasons:
    • Hypothermia > impaired renal concentrating ability > cold diuresis
    • Pts are prone to rhabdomyolysis
    • Intravascular volume is lost due to extravascular shift
• CPR
  • Only perform if pt 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
• Dysrhythmias
  • Occur once temp <30C (86F)
  • 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
    • May be refractory to therapy until pt is rewarmed
    • Attempt defibrillation
      • Value of deferring repeat defibrillation until a target temperature is reached is uncertain
      • Reasonable to perform further defibrillation attempts concurrent with rewarming
• Antibiotics
  • Give if suspect sepsis (e.g. hypothermia fails to correct w/ rewarming measures)
• Thiamine
  • Consider if Wernicke disease is possible cause of hypothermia (e.g. alcoholic pt)
• Hydrocortisone
  • Consider if pt has history of adrenal suppression or insufficiency
  • 100mg Hydrocortisone
• Thyroxine
  • Consider if any suspicion for hypothyroidism/myxedema coma
  • Could cause dysrhythmia or cardiac ischemia if not in myxedema coma

Rewarming

• Passive
  • Consider in pt w/ mild hypothermia who is able to generate intrinsic heat
  • Techniques
    • Removal from cold environment
    • Insulation
• Active
  • Consider in:
    • Moderate-severe hypothermia
    • Mild hypothermia in pt who is unstable or cannot generate intrinsic heat
    • Failure to respond to passive external rewarming
    • May be ineffective in pts w/ poor perfusion or in cardiac arrest
  • Techniques
    • Rewarm trunk BEFORE the extremities
      • Otherwise may lead to hypotension ("core temperature afterdrop")
        • Warmed vasodilated peripheral tissue allows cooler blood in extremities to circulate back to core
    • Warm water immersion
    • Heating blankets
    • Radiant heat
    • Forced air - Bair hugger
    • Warm humidified air
• Active Internal
  • Consider alone or along with active external warming in:
    • Cardiovascular instability / life-threatening dysrhythmias
    • Severe hypothermia
    • Moderate hypothermia which fails to respond to less aggressive measures
  • Techniques
    • Heated IV fluids: 65°C > 45°C more efficacious
      • If central line is placed avoid irritating the heart
    • GI tract lavage
    • Bladder lavage
    • Pleural lavage
    • Peritoneal lavage
    • Bypass/ECMO/AV Dialysis

Complications

• Acid-base disorders
• Aspiration pneumonia
• Bleeding
  • Decreased platelet function and inhibition of coagulation cascade
• Cold injuries
• Dysrhythmias
• Disseminated Intravascular Coagulation
• Pancreatitis
• Rhabdomyolysis
• Thromboembolism
  • Secondary to hemoconcentration, increased blood viscosity, and poor circulation
• Ineffective Drugs
  • Protein binding increases as body temperature drops, and most drugs become ineffective
  • Pharmacologic manipulation of the pulse and blood pressure generally should be avoided
  • Orally meds poorly absorbed because of decreased gastrointestinal motility
  • Intramuscular route avoided due to poor absorption from vasoconstricted sites

External Links

• LITFL Hypothermia

See Also

• Therapeutic hypothermia
• Water-related injuries