HYPOTHERMIA

    DEFINITION

    Definitions vary, but typically a fall in core body temperature below
    35°C (95°F).  It may be slight (32 to 35°C), moderate (27 to 32°C),
    severe (20 to 27°C) or profound (< 20°C).

    TOXIC CAUSES

    Alcohols
    Alpha-blockers
    Hypoglycaemic agents
    Nefazoline
    Opioids
    Phenothiazines
    Sedatives

    NON-TOXIC CAUSES

    Central nervous system injury
    Environmental
    Sepsis

    CLINICAL FEATURES

    Clinical signs and symptoms depend on the degree of hypothermia. 
    Progressive CNS depression is observed with decreasing core body
    temperature. The diagnosis is made by the measurement of a core
    temperature of less than 35°C (using either a low-reading thermometer
    or thermocouple).  Lethargy usually occurs at temperatures less than
    32°C, and lack of response to verbal stimuli at temperatures less than
    27°C.  In mild to moderate hypothermia, tachycardia, hyperventilation,
    and shivering are observed but at temperatures below 27°C, these
    thermoregulatory responses are lost, shivering ceases, and progressive
    bradycardia and hypoventilation are observed.  In profound hypothermia
    (less than 20°C), the patient may appear to be dead.  In severe
    hypothermia, the myocardium is very sensitive and prone to
    fibrillation.  Arterial blood gases are difficult to interpret, even
    when corrected for temperature.  ECG abnormalities (depression of
    cardiac conduction, Osborne waves, ST segment and T wave
    modification), bradycardia, hypotension and relative hypovolaemia are
    also seen.

    RELEVANT INVESTIGATIONS

    Arterial blood gases 
    Clinical chemistry, including serum electrolytes, serum creatinine,
    blood urea, blood glucose concentration, creatine phosphokinase
    activity and liver function tests.
    Chest x-ray
    Electrocardiograph
    Toxicology screening

    TREATMENT

    Symptomatic and supportive care.  Fluids given parenterally should be
    warmed to between 40 and 42°C.

    In mild to moderate cases, passive external rewarming (e.g. covering
    with blankets at room temperature) is sufficient.

    Active core rewarming is generally reserved for severely hypothermic
    patients unresponsive to passive external rewarming and/or with
    unstable cardiac rhythms (ventricular tachycardia or fibrillation,
    asystole).  It may be undertaken by: administration of heated,
    humidified oxygen; gastric lavage with warm fluids; peritoneal lavage
    with warmed dialysate; or extracorporeal methods (haemodialysis,
    cardiopulmonary or femoral-femoral bypass).

    Standard criteria of brain death do no apply to hypothermic patients
    and, if required, cardiac resuscitation should be performed until the
    patient is warm.  Standard therapy for ventricular fibrillation is
    often unsuccessful until hypothermia is corrected.

    CLINICAL COURSE AND MONITORING

    Arterial blood gases
    Core temperature (using low-reading thermometer or thermocouple)
    Continuous ECG
    Repeat analytical toxicology when indicated
    Routine clinical chemistry including serum electrolytes, serum
    creatinine, blood urea, blood glucose, creatine phosphokinase activity
    and liver function tests.

    Continue monitoring until core temperature is greater than 35°C.

    LONG-TERM COMPLICATIONS

    Hypoxic organ damage may result in long-term organ dysfunction.

    AUTHOR(S)/REVIEWERS

    Author:             Dr Albert J. Nantel,
                        Directeur, Centre de Toxicologie du Québec
                        Québec
                        Canada

    Peer Review:        Cardiff 9/96: M. Burger, J. Deng,
                        L. Fruchtengarten, L Lubomirov, T Meredith,
                        H Persson.