para>More common due to lower metabolic rate, impaired ability to maintain normal body temperature, and impaired ability to detect temperature changes �
Prevalence
Estimates vary widely due to lack of pathologic evidence, and it is typically a secondary cause when diagnosing disorders. �
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. �
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]. �
- 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. �
- Mild (32-35 �C)
- Lethargy and mild confusion
- Shivering
- Tachypnea
- Tachycardia
- Loss of fine motor coordination
- Increased BP
- Peripheral vasoconstriction
- Moderate (28-32 �C)
- Delirium
- Bradycardia
- Hypotension
- Hypoventilation
- Cyanosis
- Arrhythmias (prolonged PR interval, AV junctional rhythm, accelerated idioventricular rhythm, prolonged QT interval, altered T waves)
- Semicoma and coma
- Muscular rigidity
- Generalized edema
- Slowed reflexes
- Severe (<28 �C)
- Very cold skin
- Rigidity
- Apnea
- Bradycardia
- No pulse: ventricular fibrillation or asystole
- Areflexia
- Unresponsive
- Fixed 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) �
Diagnostic Procedures/Other
EKG �
Test Interpretation
Serum potassium >12 mmol/L associated with nonsurvival �
TREATMENT
GENERAL MEASURES
- 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].
- Give warm humidified oxygen if available.
- See "Admission Criteria/Initial Stabilization."�
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 μg for myxedema
- For severe acidosis: sodium bicarbonate
- Precautions
- Medications including epinephrine, lidocaine, and procainamide can accumulate to toxic levels if used repeatedly. Should be avoided until core temperature is >30 �C:
- When temperature reaches >30 �C, 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 �C/hr is appropriate.
- If not, then a faster rate of >2 �C/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 hypothermia
- Passive rewarming
- Administration of heated IV solutions
- Provide warm fluids by mouth if fully alert.
- Moderate hypothermia
- Active external rewarming with forced warm air systems
- Severe hypothermia (active internal [core] rewarming)
- Minimally invasive
- Heated IV fluids
- Heated humidified oxygen
- Body cavity lavage
- Thoracic cavity lavage (40-45 �C)
- Peritoneal lavage (40-45 �C)
- Extracorporeal blood rewarming
- Cardiopulmonary bypass
- Extracorporeal membrane oxygenation
- Continuous arteriovenous rewarming
- Hemodialysis and hemofiltration
- Cardiac arrhythmias
- Atrial 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 �C.
IV Fluids
- Normal saline is preferred (1)[C].
- Heat IVs from 40 �C to 45 �C 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. �
Discharge Criteria
Discharge from emergency department once normothermic, if mild hypothermia and no predisposing conditions or complications, and has suitable place to go. �
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
- During acute episode
- Monitor cardiac rhythm.
- Monitor electrolytes and glucose frequently.
- Monitor urinary output.
- Follow blood gases.
- Following acute episode
- Continued therapy for any underlying disorder
DIET
Warm fluids only if alert and able to swallow �
- 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 �K, Giesbrecht �GG, Danzl �DF, 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 �P, Henriksson �O, Naredi �P, 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 �RR, Brunette �DD. The evaluation and management of accidental hypothermia. Respir Care. 2004;49(2):192-205.44 van der Ploeg �GJ, Goslings �JC, Walpoth �BH, et al. Accidental hypothermia: rewarming treatments, complications and outcomes from one university medical centre. Resuscitation. 2010;81(11):1550-1555.
ADDITIONAL READING
- Brown �DJ, Brugger �H, Boyd �J, et al. Accidental hypothermia. N Engl J Med. 2012;367(20):1930-1938.
- Petrone �P, Asensio �JA, Marini �CP. 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 �
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 �C ("not dead until warm and dead"�).
- 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