Classified as accidental or intentional as found with cardiac bypass procedures.

Primary accidental type is due to environmental exposure to cold with no underlying medical condition responsible.

Approximately 1500 of deaths each year from accidental hypothermic injuries.

Temperatures of mild hypothermia 32-25C are tolerated well with no significant morbidity or mortality.

Mortality for hypothermia of moderate degree about 21% with core body temperature 29-32C, and increased mortality for core temperatures below 28C.

An involuntary drop in core body temperature <35*C is associated with significant morbidity and mortality.

Hypothermia, defined as a core body temperature of 36C or less, induces shivering, which has been shown to increase oxygen demands by as much as 500%.

Aside from chilling and shivering, bodily cooling produces a number of cardiovascular changes such as bradycardia, reduced cardiac output, higher mean arterial pressure, increased cardiac stress, and greater vascular resistance.

Hypothermia is particularly worrisome as core body temperature approaches 35C or less, which is sufficient to induce angina, cardiac arrhythmias, and myocardial infarctions.

Following cold exposure the body attempts to maintain a normal core temperature by means of active movement and involuntary shivering.

Primary hypothermia occurs when the heat production of a healthy person is overcome by stress of excessive cold, especially when the energy stores of the body are depleted.

Secondary hyperthermia can occur in ill persons with a wide variety of medical conditions, even in a warm environment.

Secondary hypothermic conditions include: anorexia nervosa, CVA, CNS trauma, hypothalamic dysfunction, metabolic insufficiency, neoplasms, Parkinson’s disease, medications, subarachnoid hemorrhage,spinal cord transaction, neuropathy, alcoholism, diabetic ketoacidosis, hypoadrenalism, hypopituitarism, lactic acidosis, hypoglycemia, malnutrition, extreme physical exertion, recent birth, advanced age, impaired shivering ability, burns , cold infusions, heatstroke, carcinomatosis, cardiopulmonary disease, major infections,multisystem trauma, and shock.

Most cases related to environmental exposure from drug abuse, alcoholism, mental illness and homelessness.

Outdoorsmen including hunters, skiers, climbers, boat enthusiast and swimmers are also subject to exposure to cold.

The very young and elderly are at increased risk.

Diagnosis is usually evident with recent exposure to cold, but in mild cases patients may present with confusion, dizziness, chills and shortness of breath.

Along with impaired mental status patients may have ataxia, slurred speech and paradoxically trying to remove clothing.

With profound disease may present with coma or cardiac arrest.

The elderly more likely to present with chronic or secondary hypothermia.

Local injury (frostbite) worsened by tobacco use, diabetes and peripheral neuropathy.

Mild presentation with temperatures of 32-35C associated with confusion, shivering, impaired fine motor movement and lethargy.

With moderate presentation with temperature of 28-32C patients have delirium and slowing of reflexes.

With presentation of severe degree with temperature <28C patients will have coma, difficulty breathing ad cardiac rhythm abnormalities.

Three stages of systemic cold injury:

Stage 1: core temperature 35-37 degrees C.

Associated with strong shivering and piloerection

Poor fine motor coordination, hands become numb.

Stage 2:

Core temperature 32-34.9 degrees C

Violent shivering, pallor, distal cyanosis.

Poor gross motor coordination, stumbling

Confusion despite alertness.

Stage 3:

Core temperature <32 degrees C.

Cessation of shivering, reduced level of consciousness progressing to stupor.

Paradoxical behaviors, such as burrowing and undressing.

Bradycardias and tachyarrhythmias, reduced respiration

cold diuresis, organ failure, death.

Affects almost all organs with the major effects on the cardiovascular and the central nervous systems.

Up to half of patients dying from hypothermia experience paradoxical behaviors of burrowing and undressing.

Paradoxical behaviors seen in hypothermia felt to be due to hypothalamic dysfunction that occurs when core temperatures are at or below 32 degrees C, and is associated with s sensation of extreme warmth.

Decreases cardiac pacemaker depolarization, resulting in bradycardia.

Secondary bradycardia is not mediated by the vagus nerve and may be refractory to atropine.

The mean arterial blood pressure and cardiac output are decreased.

EKG changes may include characteristic J or Osborne waves (J waves may be a normal variant but can be seen in myocardial ischemia and sepsis on occasion).

Can be associated with atrial and ventricular arrhythmias.

At core temperatures below 25C asystole and ventricular fibrillation may occur.

CNS metabolism decreases in a linear fashion as core body temperature drops, with electrical brain activity becoming abnormal with temperatures less then 33C and the EEG may suggest brain death if temperature reaches 19-20C.

Clinical findings include shivering of all extremities with core body temperature between 32-35C, dysarthria, impaired mental status and increased respiratory rate with temperatures below 34C, ataxia and apathy are seen at 33C, at 32C deepening CNS depression occurs and stupor begins, at 30C arrhythmias occur with increasing bradycardia and decreased cardiac output, between 28-30C pupils may dilate and become minimally reactive to light, and below 28C cardiac contractility worsens, ventricular fibrillation can occur, rigidity, apnea, areflexia, coma and fixed pupils may occur.

In comatose survivors of out of hospital cardiac arrest, a target temperature of 31°C did not significantly reduce the rate of death or poor neurologic outcome at 180 days compared with the target temperature of 34°C.

Treated by external or internal rewarming.

In mild cases passive rewarming by improving retention of the body’s warmth by utilizing dry insulation is indicated.

In severe cases active external rewarming is required and include: forced air warming blankets, radiant warmers and immersion hydrotherapy.

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