BASICSScott T. Henderson, MD
BASICS
DESCRIPTION
• A core temperature of <35°C (95°F)
• May take several hours to days to develop
• Patients with cold-water immersion can appear to be dead but can still be resuscitated.
• System(s) affected: all body systems
• Synonym(s): accidental hypothermia
EPIDEMIOLOGY
• Predominant age: very young and the elderly
• Predominant sex: male > female
Geriatric Considerations
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.
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.
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.
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.
Dry patient.
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
– 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.
ADMISSION, INPATIENT, AND NURSING CONSIDERATIONS
• 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.
• 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
• Avoid fluid overload.
• Avoid overheating dextrose solutions; dextrose caramelizes at 60°C.
• Avoid lactated Ringer solution because of decreased lactate metabolism.
• Because of the cold, heart is irritable and susceptible to arrhythmias; take special care in moving and transporting.
• 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.
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
1. 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.
2. 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.
3. Kempainen RR, Brunette DD. The evaluation and management of accidental hypothermia. Respir Care. 2004;49(2):192–205.
4. 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
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