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Hypothermia

- Prehospital (1)[C] - Factors to guide treatment - Level of consciousness - Shivering intensity - Cardiovascular stability based on blood pressure and cardiac rhythm. - ABCs of basic life support - Remove wet garments. - Protect against heat loss and wind chill. - If far from definitive care, begin active rewarming but do not delay transport. - Mild hypothermic patients with shivering ability will have improved comfort and might have a reduced cold-stress response with active rewarming (2)[B].

- Monitor core temperature; use a consistent method. - Monitor BP and cardiac rhythm. - Correct metabolic acidosis. - Evaluate for frostbite and other trauma. - Mild hypothermia - Passive rewarming - Administration of heated IV solutions - Provide warm fluids by mouth if fully alert.

- Extracorporeal blood rewarming - Cardiopulmonary bypass - Extracorporeal membrane oxygenation - Continuous arteriovenous rewarming - Hemodialysis and hemofiltration

- Following acute episode - Continued therapy for any underlying disorder

para>More common due to lower metabolic rate, impaired ability to maintain normal body temperature, and impaired ability to detect temperature changes пїЅ

Prevalence

Estimates vary widely due to lack of pathologic evidence, and it is typically a secondary cause when diagnosing disorders. пїЅ

ETIOLOGY AND PATHOPHYSIOLOGY

  • Overwhelming environmental cold stress
  • Decreased heat production
  • Increased heat loss
  • Impaired thermoregulation

RISK FACTORS

  • Alcohol consumption
  • Bronchopneumonia
  • Cardiovascular disease
  • Cold-water immersion
  • Dermal dysfunction (burns, erythrodermas)
  • Drug intoxication
  • Endocrinopathies (myxedema, severe hypoglycemia)
  • Excessive fluid loss
  • Hepatic failure
  • Hypothalamic and central nervous system (CNS) dysfunction
  • Malnutrition
  • Mental illness; Alzheimer disease
  • Prolonged cardiac arrest
  • Prolonged environmental exposure
  • Renal failure
  • Sepsis
  • Trauma (especially head)
  • Uremia

GENERAL PREVENTION

  • Appropriate clothing, with particular attention to head, feet, and hands
  • For outdoor activities, carry survival bags with rescue foil blanket for use if stranded or injured.
  • Avoid alcohol.
  • Alertness to early symptoms and initiating preventive steps (e.g., drinking warm fluids)
  • Identify medications that may predispose to hypothermia (e.g., neuroleptics, sedatives, hypnotics, tranquilizers).

COMMONLY ASSOCIATED CONDITIONS

  • Addison disease
  • CNS dysfunction
  • Congestive heart failure
  • Diabetes
  • Hypopituitarism
  • Hypothyroidism
  • Ketoacidosis
  • Pulmonary infection
  • Sepsis
  • Uremia

DIAGNOSIS

HISTORY

Presentation varies with the temperature of the patient at the time of presentation. пїЅ

ALERT

History of prolonged exposure to cold may make the diagnosis obvious, but hypothermia may be overlooked in other situations, especially in comatose patients.

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PHYSICAL EXAM

Esophageal temperature is most accurate, minimally invasive method of assessing core temperature (1)[C]. пїЅ

  • Must have secure airway
  • Probe inserted into lower third of esophagus

Exam findings vary with the temperature of the patient at the time of presentation. пїЅ

  • Mild (32-35 пїЅC)Lethargy and mild confusionShiveringTachypneaTachycardiaLoss of fine motor coordinationIncreased BPPeripheral vasoconstriction
  • Moderate (28-32 пїЅC)DeliriumBradycardiaHypotensionHypoventilationCyanosisArrhythmias (prolonged PR interval, AV junctional rhythm, accelerated idioventricular rhythm, prolonged QT interval, altered T waves)Semicoma and comaMuscular rigidityGeneralized edemaSlowed reflexes
  • Severe (<28 пїЅC)Very cold skinRigidityApneaBradycardiaNo pulse: ventricular fibrillation or asystoleAreflexiaUnresponsiveFixed pupils

ALERT

Use specially designed thermometers that can record low temperatures and measure core temperatures.

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Pediatric Considerations

  • Infants may present with bright red, cold skin and very low energy.
  • A child's body temperature drops faster than an adult does when immersed in cold water.

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DIFFERENTIAL DIAGNOSIS

  • Cerebrovascular accidents
  • Intoxication
  • Drug overdose
  • Complications of diabetes, hypothyroidism, hypopituitarism

DIAGNOSTIC TESTS & INTERPRETATION

Initial Tests (lab, imaging)

  • Arterial blood gases (corrected for temperature)
  • CBC and platelet counts
  • Serum electrolytes
  • Urinalysis
  • Coagulation studies
  • Fibrinogen levels
  • Blood culture
  • BUN/creatinine
  • Glucose
  • Amylase
  • Liver function studies
  • Cardiac enzymes
  • Calcium
  • Magnesium
  • Alcohol level
  • Drug screen
  • Cervical spine, chest, and abdomen x-rays, if appropriate

Follow-Up Tests & Special Considerations

Serum cortisol and TSH if underlying endocrine dysfunction (hypothalamus stimulates release of hormones in response to hypothermia) пїЅ

Diagnostic Procedures/Other

EKG пїЅ

Test Interpretation

Serum potassium >12 mmol/L associated with nonsurvival пїЅ

TREATMENT

GENERAL MEASURES

  • Prehospital (1)[C]Factors to guide treatmentLevel of consciousnessShivering intensityCardiovascular stability based on blood pressure and cardiac rhythm.ABCs of basic life supportRemove wet garments.Protect against heat loss and wind chill.If far from definitive care, begin active rewarming but do not delay transport.Mild hypothermic patients with shivering ability will have improved comfort and might have a reduced cold-stress response with active rewarming (2)[B].Give warm humidified oxygen if available.
  • See "Admission Criteria/Initial Stabilization."пїЅ

MEDICATION

  • For sepsis or bacterial infections: Antibiotics based on site and etiology.
  • For hypoglycemia: D50W at a dose of 1 mg/kg
  • Thiamine: 100 mg, if alcoholic or cachectic
  • Naloxone: 2 mg
  • Levothyroxine: 150 to 500 Ојg for myxedema
  • For severe acidosis: sodium bicarbonate
  • PrecautionsMedications including epinephrine, lidocaine, and procainamide can accumulate to toxic levels if used repeatedly. Should be avoided until core temperature is >30 пїЅC:When temperature reaches >30 пїЅC, IV medications are indicated but at longer than the standard intervals.It may be reasonable to consider vasopressors during cardiac arrest according to standard ACLS algorithm with concurrent rewarming.
  • Significant possible interactions:Use all drugs cautiously due to impaired metabolism and renal elimination.
  • Once rewarming has occurred, there is mobilization of depot stores.
  • Routine use of steroids or antibiotics does not increase survival or decrease postresuscitative damage.

INPATIENT CONSIDERATIONS

Admission Criteria/Initial Stabilization

  • Rewarming depends on severity of hypothermia and presence of cardiac arrest.
  • If no cardiac arrest, consider active external rewarming (3)[B].
  • If cardiac arrest is present, consider active internal rewarming (3)[B].
  • Warm center of body first (4)[C].
  • The rate of rewarming is determined by whether a perfusing cardiac output is present.If a perfusing cardiac output is present, 1-2 пїЅC/hr is appropriate.If not, then a faster rate of >2 пїЅC/hr should be used.
  • Monitor core temperature; use a consistent method.
  • Monitor BP and cardiac rhythm.
  • Correct metabolic acidosis.
  • Evaluate for frostbite and other trauma.
  • Mild hypothermiaPassive rewarmingAdministration of heated IV solutionsProvide warm fluids by mouth if fully alert.
  • Moderate hypothermiaActive external rewarming with forced warm air systems
  • Severe hypothermia (active internal [core] rewarming)Minimally invasiveHeated IV fluidsHeated humidified oxygenBody cavity lavageThoracic cavity lavage (40-45 пїЅC)Peritoneal lavage (40-45 пїЅC)Extracorporeal blood rewarmingCardiopulmonary bypassExtracorporeal membrane oxygenationContinuous arteriovenous rewarmingHemodialysis and hemofiltration
  • Cardiac arrhythmiasAtrial fibrillation and sinus bradycardia are common, but patients usually convert to normal sinus rhythm with rewarming.If ventricular fibrillation is present, it should be treated with one shock. If patient does not respond, consider deferring further attempts until rewarm has occurred.Do not treat transient ventricular arrhythmias.If cardiac pacing required, preferable to use external noninvasive pacemaker
  • Admit patients, preferably to the ICU, with underlying disease, physiologic abnormalities, or core temperature <32 пїЅC.

IV Fluids

  • Normal saline is preferred (1)[C].
  • Heat IVs from 40 пїЅC to 45 пїЅC when possible, but should be no colder than the patient's core temperature.

ALERT

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Nursing

Because of the cold, heart is irritable and susceptible to arrhythmias; take special care in moving and transporting. пїЅ

Discharge Criteria

Discharge from emergency department once normothermic, if mild hypothermia and no predisposing conditions or complications, and has suitable place to go. пїЅ

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Patient Monitoring

  • During acute episodeMonitor cardiac rhythm.Monitor electrolytes and glucose frequently.Monitor urinary output.Follow blood gases.
  • Following acute episodeContinued therapy for any underlying disorder

DIET

Warm fluids only if alert and able to swallow пїЅ

  • Alcohol intake increases risk of becoming hypothermic in cold conditions.
  • Encourage persons with cardiovascular disease to avoid outdoor exercise in cold weather.
  • Refer to social service agency for help with adequate housing, heat, and/or clothing, if appropriate.

PROGNOSIS

  • Mortality rates are decreasing due to increased recognition and advanced therapy.
  • Mortality usually depends on the severity of underlying cause and comorbidities.
  • In previously healthy individuals, recovery is usually complete.Mortality rate in healthy patients is <5%.
  • Mortality rate in patients with coexisting illness is >50%.

Geriatric Considerations

Mortality rates increase with increasing age.

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COMPLICATIONS

  • Core temperature after drop
  • Cardiac arrhythmias
  • Hypotension
  • Hyperkalemia
  • Hypoglycemia
  • Rhabdomyolysis
  • Sepsis
  • Pneumonia (aspiration and broncho)
  • Pulmonary edema
  • Acute respiratory distress syndrome
  • Pancreatitis
  • Peritonitis
  • GI bleeding
  • Ileus
  • Acute tubular necrosis
  • Bladder atony
  • Intravascular thromboses/disseminated intravascular coagulation
  • Metabolic acidosis
  • Gangrene of extremities
  • Compartment syndromes
  • Seizures
  • Cerebral ischemia
  • Delirium

REFERENCES

11 Zafren пїЅK, Giesbrecht пїЅGG, Danzl пїЅDF, et al. Wilderness Medical Society practice guidelines for the out-of-hospital evaluation and treatment of accidental hypothermia: 2014 update. Wilderness Environ Med. 2014;25(4)(Suppl):S66-S85.22 Lundgren пїЅP, Henriksson пїЅO, Naredi пїЅP, et al. The effect of active warming in prehospital trauma care during road and air ambulance transportation-a clinical randomized trial. Scand J Trauma Resusc Emerg Med. 2011;19:59.33 Kempainen пїЅRR, Brunette пїЅDD. The evaluation and management of accidental hypothermia. Respir Care. 2004;49(2):192-205.44 van der Ploeg пїЅGJ, Goslings пїЅJC, Walpoth пїЅBH, et al. Accidental hypothermia: rewarming treatments, complications and outcomes from one university medical centre. Resuscitation. 2010;81(11):1550-1555.

ADDITIONAL READING

  • Brown пїЅDJ, Brugger пїЅH, Boyd пїЅJ, et al. Accidental hypothermia. N Engl J Med. 2012;367(20):1930-1938.
  • Petrone пїЅP, Asensio пїЅJA, Marini пїЅCP. Management of accidental hypothermia and cold injury. Curr Probl Surg. 2014;51(10):417-431.

SEE ALSO

  • Frostbite; Near Drowning
  • Algorithm: Hypothermia

CODES

ICD10

  • T68.XXXA Hypothermia, initial encounter
  • T68.XXXD Hypothermia, subsequent encounter
  • T68.XXXS Hypothermia, sequela

ICD9

991.6 Hypothermia пїЅ

SNOMED

  • 386689009 Hypothermia (finding)
  • 83966006 Hypothermia due to cold environment (disorder)
  • 241970005 Hypothermia due to exposure (disorder)

CLINICAL PEARLS

  • Most common cause of hypothermia in the United States is cold exposure due to alcohol intoxication.
  • With a severely decreased core temperature, one should assume resuscitation, if possible, unless there are obvious lethal injuries. Continue resuscitation and rewarm to 33-35 пїЅC ("not dead until warm and dead"пїЅ).
  • ECG changes are associated with hypothermia: slowing of sinus rate with T-wave inversion; QT, QRS, and PR interval prolongation; atrial and ventricular arrhythmias; hypothermic J waves (Osborn waves) characterized by a notching of the QRS complex and ST segment