Hypothermia, Emergency Medicine

Basics

Description

Body temperature <35 �C
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

Etiology

Dermal disease:
- Burn
- Exfoliative dermatitis
- Severe psoriasis
Drug induced:
- Ethanol
- Phenothiazines
- Sedative-hypnotics
Environmental:
- Immersion
- Nonimmersion
Iatrogenic:
- Aggressive fluid replacement
- Heat stroke treatment
Metabolic:
- Hypoadrenalism
- Hypopituitarism
- Hypothyroidism
Neurologic:
- Acute spinal cord transection
- Head trauma
- Stroke
- Tumor
- Wernicke disease
Neuromuscular inefficiency:
- Age extreme
- Impaired shivering
- Lack of acclimatization
Sepsis

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

Diagnosis

Signs and Symptoms

Mild (35-32.2 �C/95-90 �F):
- 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 �C/90-82.4 �F):
- 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
- Dilated pupils
- Diminished gag reflex
- Extinction of shivering
- Hyporeflexia
- Hypotension
- J-wave (Osborn wave) on ECG
Severe (<28 �C/<82.4 �F):
- Apnea
- Coma
- Decreased or no activity on EEG (electroencephalography)
- Nonreactive pupils
- Oliguria:
  - Renal blood flow depressed 50%
- Pulmonary edema
- Ventricular dysrhythmias/asystole:
  - Cardiac cycle lengthens, resulting in increased intervals

History
Time of submersion for near drowning in cold water. �
Physical Exam

May not be able to palpate pulse
May not be able to obtain BP
Pupils dilate <26 �C

Essential Workup

Accurate core temperature confirms diagnosis. �

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 bradycardia
- Atrial fibrillation with slow response
- Ventricular fibrillation
- Asystole
- Prolonged PR, QRS, QT intervals
- J-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"�:
- CPR recommended during transport:
Prolonged palpation/auscultation for cardiac activity: 30-45 sec
- Apparent cardiovascular collapse may be depressed cardiac output, often sufficient to meet metabolic demands.

Initial Stabilization/Therapy

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.
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 �C
  - Defibrillate 1-3 times and then again post rewarming.
  - Once >30 �C, if ventricular fibrillation persists consider amiodarone.
  - Direct current results in myocardial damage.
Dysrhythmia management:
- Atrial fibrillation:
  - Commonly <32 �C
  - Usually converts spontaneously
- Malignant ventricular dysrhythmias:
  - Amiodarone drug of choice though limited proof of effectiveness.
Rewarming techniques:
- Faster rewarming rates (1-2 �C/hr) generally have better prognosis than slower rewarming rates (<0.5 �C/hr).
- Active rewarming is necessary at core temperature of <32 �C:
  - Internal thermogenesis insufficient to increase body temperature
  - Shivering extinguished
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 �C/hr
- Disadvantage: Core rises very slowly.
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.
Active core rewarming techniques:
- Airway rewarming (complete humidification at 40-45 �C):
  - Administer to all patients.
- Heated IV (40-42 �C) 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 recommended
  - Low amount of surface area
  - Aspiration risk if airway not secured
- Pleural irrigation (0.9 NS at 30-42 �C):
  - 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 �C):
  - Use in unstable hypothermic patients or stable patients with severe hypothermia whose rewarming rates are <1 �C/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.
- Continuous arteriovenous rewarming:
  - BP must be >60 mm Hg.
  - Blood circulated through warmer from percutaneously inserted femoral arterial and contralateral venous catheters
- Extracorporeal venovenous rewarming:
  - Blood is removed via central venous catheter, heated to 40 �C, 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 dependence
- Empiric 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 μg 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 �C)
Young, healthy patients with no comorbid illness who have mild accidental hypothermia (>32 �C) 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 �C) 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 �

Pearls and Pitfalls

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

Additional Reading

Brown �D, Brugger �H, Boyd �J, et al. Accidental hypothermia. N Engl JMed. 2012;367:1930-1938.
Corneli �HM. Accidental hypothermia. Pediatr Emerg Care. 2012;28(5):475-480.
Jurkovich �GJ. Environmental cold-induced injury. Surg Clin North Am. 2007;87:247-267.
Laniewicz �M, Lyn-Kew �K, Silbergleit �R. Rapid endovascular warming for profound hypothermia. Ann Emerg Med. 2008;51(2):160-163.
McCullough �L, Arora �S. Diagnosis and treatment of hypothermia. Am Fam Physician. 2004;70:2325-2332.

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

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