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Hypothermia, Emergency Medicine

Basics

Description

- Body temperature <35 пїЅC - Risk factors: - Poor temperature regulation: - Very young - Advanced age - Comorbid condition - Intoxication

- Pathophysiology: - Loss of heat: - Radiation: Most rapid, 50% of heat loss - Conduction - Convection - Evaporation - Respiration

- Heat production: - Shivering - Nonshivering thermogenesis - Increased thyroxine - Increased epinephrine

- Dermal disease: - Burn - Exfoliative dermatitis - Severe psoriasis

- Drug induced: - Ethanol - Phenothiazines - Sedative-hypnotics

- Metabolic: - Hypoadrenalism - Hypopituitarism - Hypothyroidism

- Neuromuscular inefficiency: - Age extreme - Impaired shivering - Lack of acclimatization

- Mild (35-32.2 пїЅC/95-90 пїЅF): - Initial excitation phase to combat cold: - HTN - Shivering - Tachycardia - Early tachycardia followed by bradycardia - Tachypnea - Vasoconstriction

- Over time with onset of fatigue: - Apathy - Ataxia - Cold diuresis - Defect in distal tubular reabsorption of sodium and water - Impaired judgment

- Moderate (32.2-28 пїЅC/90-82.4 пїЅF): - Atrial dysrhythmias - Bradycardia: - Decreased spontaneous depolarization of pacemaker cells - Refractory to atropine

- Decreased level of consciousness - Decreased respiratory rate: - Progressive respiratory depression with CO2 retention

- Severe (<28 пїЅC/<82.4 пїЅF): - Apnea - Coma - Decreased or no activity on EEG (electroencephalography) - Nonreactive pupils - Oliguria: - Renal blood flow depressed 50%

- ABCs: - Supplemental oxygen - Oral and nasotracheal intubation are safe. - Place nasogastric (NG) tube postintubation. - Cardiac monitor - Warmed D5.9 NS preferred over lactated Ringer: - Shivering depletes glycogen.

- Passive external rewarming: - Ideal technique for most healthy patients with mild hypothermia - Must have intact thermoregulatory mechanisms, normal endocrine function, and adequate energy stores - Cover the patient with dry insulating material. - Endogenous thermogenesis must generate an acceptable rate of rewarming: - Must increase 0.5-2 пїЅC/hr

- Active external rewarming: - Delivers heat directly to the skin - Safe in previously healthy, young, acutely hypothermic victims - Requires intact circulation to remove peripherally rewarmed blood to core - Associated with core temperature afterdrop - Rewarming shock: Venous pooling in warmed extremities secondary to vasodilatation - Cover trunk preferentially. - Bair Hugger device provides forced warm air: Prevents shock or afterdrop.

- Heated gastric irrigation via NG or orogastric tubes: - Not recommended - Low amount of surface area - Aspiration risk if airway not secured

- Pleural irrigation (0.9 NS at 30-42 пїЅC): - Use in severe hypothermia without cardiac activity. - 1-2 chest tubes; midaxillary and midclavicular bilaterally - Contraindicated in patients with cardiac rhythm because the chest tube may induce ventricular fibrillation

- Heated peritoneal lavage (0.9 NS at 40-45 пїЅC): - Use in unstable hypothermic patients or stable patients with severe hypothermia whose rewarming rates are <1 пїЅC/hr. - 1-2 catheters - Advantageous in patients with overdose or rhabdomyolysis

- Extracorporeal rewarming: - Most effective rewarming method - Hemodialysis: - Initiate for patients with drug overdoses or severe electrolyte disturbances.

  • Body temperature <35 пїЅC
  • Risk factors:Poor temperature regulation:Very youngAdvanced ageComorbid conditionIntoxication
  • Pathophysiology:Loss of heat:Radiation: Most rapid, 50% of heat lossConductionConvectionEvaporationRespirationHeat production:ShiveringNonshivering thermogenesisIncreased thyroxineIncreased epinephrine

Etiology

  • Dermal disease:BurnExfoliative dermatitisSevere psoriasis
  • Drug induced:EthanolPhenothiazinesSedative-hypnotics
  • Environmental:
  • Iatrogenic:Aggressive fluid replacementHeat stroke treatment
  • Metabolic:HypoadrenalismHypopituitarismHypothyroidism
  • Neurologic:Acute spinal cord transectionHead traumaStrokeTumorWernicke disease
  • Neuromuscular inefficiency:Age extremeImpaired shiveringLack of acclimatization
  • Sepsis

Infants have a large body surface to mass ratio Child abuse. пїЅ

Diagnosis

Signs and Symptoms

  • Mild (35-32.2 пїЅC/95-90 пїЅF):Initial excitation phase to combat cold:HTNShiveringTachycardiaEarly tachycardia followed by bradycardiaTachypneaVasoconstrictionOver time with onset of fatigue:ApathyAtaxiaCold diuresisDefect in distal tubular reabsorption of sodium and waterImpaired judgment
  • Moderate (32.2-28 пїЅC/90-82.4 пїЅF):Atrial dysrhythmiasBradycardia:Decreased spontaneous depolarization of pacemaker cellsRefractory to atropineDecreased level of consciousnessDecreased respiratory rate:Progressive respiratory depression with CO2 retentionDilated pupilsDiminished gag reflexExtinction of shiveringHyporeflexiaHypotensionJ-wave (Osborn wave) on ECG
  • Severe (<28 пїЅC/<82.4 пїЅF):ApneaComaDecreased or no activity on EEG (electroencephalography)Nonreactive pupilsOliguria:Renal blood flow depressed 50%Pulmonary edemaVentricular dysrhythmias/asystole:Cardiac cycle lengthens, resulting in increased intervals

History

Time of submersion for near drowning in cold water. пїЅ

Physical Exam

  • May not be able to palpate pulse
  • May not be able to obtain BP
  • Pupils dilate <26 пїЅC

Essential Workup

Accurate core temperature confirms diagnosis. пїЅ

Diagnosis Tests & Interpretation

Lab

  • Finger stick glucose
  • ABG:Temperature correction not needed
  • CBC:Hematocrit rises owing to decreased plasma volume.Leukopenia does not imply absence of infection:High-risk groups (e.g., neonate, immunocompromised) should receive empiric antibiotics.
  • Electrolytes, BUN, creatinine:Vary during rewarming; recheck frequently, especially creatine phosphokinase (CPK) and potassium (K+)
  • Serum lactate
  • PT, PTT, and platelets:Prolonged clotting times, thrombocytopenia common
  • Toxicology screen:Alcohol/drug ingestion common

Imaging

  • CXR:Pneumonia common complication
  • EKG:Tachycardia to bradycardiaAtrial fibrillation with slow responseVentricular fibrillationAsystoleProlonged PR, QRS, QT intervalsJ-wave (Osborn waves)ST-elevation mimicking acute coronary syndrome

Differential Diagnosis

  • Environmental
  • Sepsis
  • Primary CNS disorder
  • Metabolic
  • Drug induced

Treatment

Pre-Hospital

  • Patient is not dead until "Warm and Dead"пїЅ:CPR recommended during transport:
  • Prolonged palpation/auscultation for cardiac activity: 30-45 secApparent cardiovascular collapse may be depressed cardiac output, often sufficient to meet metabolic demands.

Initial Stabilization/Therapy

  • ABCs:Supplemental oxygenOral and nasotracheal intubation are safe.Place nasogastric (NG) tube postintubation.Cardiac monitorWarmed D5.9 NS preferred over lactated Ringer:Shivering depletes glycogen.
  • Remove wet clothing and begin passive external rewarming.
  • Administer Narcan, D50W (or Accu-Chek), and thiamine to a patient with altered mental status.
  • Stress-dose steroids (Solu-Cortef 100 mg IV) for known adrenal insufficiency or treatment failure.
  • Obtain accurate core temperatures using rectal thermometer.

Ed Treatment/Procedures

  • Cardiac arrest resuscitation:Most dysrhythmias correct with rewarming alone.Ventricular fibrillation induction occurs with rough handling, chest compressions, hypoxia, and acid-base changes.CPR is less effective owing to decreased chest wall elasticity.Defibrillation is rarely successful at temperatures <28-30 пїЅCDefibrillate 1-3 times and then again post rewarming.Once >30 пїЅC, if ventricular fibrillation persists consider amiodarone.Direct current results in myocardial damage.
  • Dysrhythmia management:Atrial fibrillation:Commonly <32 пїЅCUsually converts spontaneouslyMalignant ventricular dysrhythmias:Amiodarone drug of choice though limited proof of effectiveness.
  • Rewarming techniques:Faster rewarming rates (1-2 пїЅC/hr) generally have better prognosis than slower rewarming rates (<0.5 пїЅC/hr).Active rewarming is necessary at core temperature of <32 пїЅC:Internal thermogenesis insufficient to increase body temperatureShivering extinguished
  • Passive external rewarming:Ideal technique for most healthy patients with mild hypothermiaMust have intact thermoregulatory mechanisms, normal endocrine function, and adequate energy storesCover the patient with dry insulating material.Endogenous thermogenesis must generate an acceptable rate of rewarming:Must increase 0.5-2 пїЅC/hrDisadvantage: Core rises very slowly.
  • Active external rewarming:Delivers heat directly to the skinSafe in previously healthy, young, acutely hypothermic victimsRequires intact circulation to remove peripherally rewarmed blood to coreAssociated with core temperature afterdropRewarming shock: Venous pooling in warmed extremities secondary to vasodilatationCover trunk preferentially.Bair Hugger device provides forced warm air: Prevents shock or afterdrop.
  • Active core rewarming techniques:Airway rewarming (complete humidification at 40-45 пїЅC):Administer to all patients.Heated IV (40-42 пїЅC) D5.9 NS:Administer to all patients.High flow rates must be maintained.Use blood warmer or calibrated microwave.Heated gastric irrigation via NG or orogastric tubes:Not recommendedLow amount of surface areaAspiration risk if airway not securedPleural irrigation (0.9 NS at 30-42 пїЅC):Use in severe hypothermia without cardiac activity.1-2 chest tubes; midaxillary and midclavicular bilaterallyContraindicated in patients with cardiac rhythm because the chest tube may induce ventricular fibrillationHeated peritoneal lavage (0.9 NS at 40-45 пїЅC):Use in unstable hypothermic patients or stable patients with severe hypothermia whose rewarming rates are <1 пїЅC/hr.1-2 cathetersAdvantageous in patients with overdose or rhabdomyolysis
  • Extracorporeal rewarming:Most effective rewarming methodHemodialysis:Initiate for patients with drug overdoses or severe electrolyte disturbances.Continuous arteriovenous rewarming:BP must be >60 mm Hg.Blood circulated through warmer from percutaneously inserted femoral arterial and contralateral venous cathetersExtracorporeal venovenous rewarming:Blood is removed via central venous catheter, heated to 40 пїЅC, and returned via 2nd central or large peripheral venous catheter.Cardiopulmonary bypass:Treatment of choice in severe hypothermia with cardiac arrest
  • Additional therapy:Methylprednisolone or hydrocortisone for suspicion of adrenocortical insufficiency or steroid dependenceEmpiric treatment with levothyroxine only for myxedematous patients

Medication

  • Amiodarone: 300 mg IV push (IVP) for ventricular fibrillation followed by 1 mg/min infusion
  • Dextrose: D50W 1 amp-50 mL or 25 g (peds: D25W 2-4 mL/kg) IV
  • Hydrocortisone: 250 mg IVP
  • Levothyroxine: 50-500 Ојg IV over several minutes
  • Methylprednisolone: 30 mg/kg IVP
  • Naloxone (Narcan): 2 mg (peds: 0.1 mg/kg) IV or IM initial dose
  • Thiamine (vitamin B1): 100 mg (peds: 50 mg) IV or IM

Follow-Up

Disposition

Admission Criteria

  • Moderate to severe hypothermia (<32 пїЅC)
  • Young, healthy patients with no comorbid illness who have mild accidental hypothermia (>32 пїЅC) that responds well to warming:Admit to an observation area.Discharge if asymptomatic after 8-12 hr and they remain asymptomatic.

Discharge Criteria

  • Young, healthy patients with no comorbid illness
  • Very mild accidental hypothermia (>35 пїЅC) that responds well to warming
  • Safe, warm environment to go to after discharge

Followup Recommendations

Social work follow-up for homeless patients with cold exposure and hypothermia пїЅ

Pearls and Pitfalls

  • Defibrillation is rarely successful at temperatures <28-30 пїЅC:Defibrillate 1-3 times and then again post rewarming.
  • Atrial fibrillation usually converts spontaneously.
  • Faster rewarming rates (1-2 пїЅC/hr) generally have better prognosis than slower rewarming rates (<0.5 пїЅC/hr).
  • Afterdrop is the continued decline in core temp after removed from coldOngoing conduction of heat from core warming periphery prior to the core
  • Rewarming shockHypovolemic shock secondary to failure to replete volume during resuscitation.

Additional Reading

  • Brown пїЅD, Brugger пїЅH, Boyd пїЅJ, et al. Accidental hypothermia. N Engl JMed. 2012;367:1930-1938.
  • Corneli пїЅHM. Accidental hypothermia. Pediatr Emerg Care. 2012;28(5):475-480.
  • Jurkovich пїЅGJ. Environmental cold-induced injury. Surg Clin North Am. 2007;87:247-267.
  • Laniewicz пїЅM, Lyn-Kew пїЅK, Silbergleit пїЅR. Rapid endovascular warming for profound hypothermia. Ann Emerg Med. 2008;51(2):160-163.
  • McCullough пїЅL, Arora пїЅS. Diagnosis and treatment of hypothermia. Am Fam Physician. 2004;70:2325-2332.

See Also (Topic, Algorithm, Electronic Media Element)

Frostbite пїЅ

Codes

ICD9

  • 778.3 Other hypothermia of newborn
  • 780.65 Hypothermia not associated with low environmental temperature
  • 991.6 Hypothermia

ICD10

  • P80.9 Hypothermia of newborn, unspecified
  • R68.0 Hypothermia, not associated w low environmental temperature
  • T68.XXXA Hypothermia, initial encounter

SNOMED

  • 386689009 Hypothermia (finding)
  • 123461000119109 Hypothermia not associated with low environmental temperature (finding)
  • 13629008 Hypothermia of newborn (disorder)
  • 212916004 Hypothermia - accidental