Accidental hypothermia

Background

1. Definition: Core Temp <35C (95F)

Stage	Clinical Symptoms	Typical Core Temperature	Treatment
HT I	Conscious, shivering	35 to 32C	Warm environment and clothing, warm sweet drinks, active movement if possible
HT II	Impaired consciousness, not shivering	<32 to 28C	Cardiac monitoring, minimal movements to avoid arrhythmias, horizontal position and immobilization, full body insulation, active external and minimally invasive rewarming techniques (heating pads, forced-air heating packs or blankets, warm parenteral fluids)
HT III	Unconscious, not shivering, VS present	<28 to 24C	HT II plus airway management as required; ECMO or CPD in cases with cardiac instability refractory to medical management
HT IV	No VS	<24C	HT II and III plus CPR and up to three doses of epinephrine (IV or IO dose of 1mg ) and defibrillation; rearming with ECMO or CPB or CPR with active external and alternative internal rewarming

DDx

1. Impaired thermoregulation
   1. Central failure
      1. Anorexia nervosa
      2. CVA
      3. Hypothalamic dysfunction
      4. Metabolic failure
      5. Neoplasm
      6. Parkinson's
      7. Drugs-Ethanol, Sedatives-hypnotics
      8. SAH
      9. Toxins
   2. Peripheral failure
      1. Acute spinal cord transection
      2. Decreased heat production
      3. Neuropathy
   3. Endocrine
      1. DKA or AKA
      2. Hypoadrenalism
      3. Hypopituitarism
      4. Lactic acidosis (Sepsis)
   4. Insufficient energy
      1. Extreme physical exertion
      2. Hypoglycemia
      3. Malnutrition
   5. Neuromuscular compromise
      1. Recent birth or advanced age
      2. Impaired shivering
2. Increased heat loss
   1. Dermatologic
      1. Burns
      2. Exfoliative dermatitis
   2. Iatrogenic
      1. Massive fluid or blood resuscitation
      2. Emergency childbirth
      3. Heat stroke treatment
   3. Other
      1. Carcinomatosis
      2. Cardiopulmonary disease
      3. Multisystem trauma
      4. Shock

ECG

1. Typical sequence is sinus brady > a fib w/ slow ventricular response > v-fib > asystole
2. Other ECG findings:
   1. Osborn (J) wave
   2. T-wave inversions
   3. PR, QRS, QT prolongation
   4. Muscle tremor artifact
   5. AV block
   6. PVCs

Treatment

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

General

1. Handle pt gently
   1. V-fib may be induced by rough handling of pt due to irritable myocardium (anecdotal)
2. O2
   1. Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
3. IVF
   1. Reasons:
      1. Hypothermia > impaired renal concentrating ability > cold diuresis
      2. Pts are prone to rhabdo
      3. Intravascular volume is lost due to extravascular shift
4. CPR
   1. Only perform if pt truly does not have a pulse (unnecessary CPR may lead to V-fib)
   2. Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR
5. Dysrhythmias
   1. Occur once temp <30C (86F)
   2. Rewarming is treatment of choice
      1. Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
         1. Activity of antiarrhythmics is unpredictable in hypothermia
         2. Hypothermic heart is relatively resistant to atropine, pacing, and countershock
   3. V-fib
      1. May be refractory to therapy until pt is rewarmed
      2. Attempt a single defibrillation attempt
         1. If unsuccessful continue CPR and attempt defibrillation again once temp >30C (86F)
6. Abx
   1. Give if suspect sepsis (e.g. hypothermia fails to correct w/ rewarming measures)
7. Thiamine
   1. Consider if Wernicke disease is possible cause of hypothermia (e.g. alcoholic pt)
8. Hydrocortisone
   1. Consider if pt has history of adrenal suppression or insufficiency
9. Thyroxine
   1. Consider if any suspicion for hypothyroidism/myxedema coma

Rewarming

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

Complications

1. Aspiration PNA
2. DIC
3. Bleeding

Source

Tintinalli

See Also

• Therapeutic Hypothermia