Laboratory Studies
Arterial blood gas determination includes the following:
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Blood gas analyzers warm blood to 37°C.
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As a fluid is heated, gases become soluble. Therefore, the arterial blood gas (ABG) may report a falsely elevated oxygen and carbon dioxide level in patients who are hypothermic. The blood gas analyzer may also report a lower pH than a patient's actual values.
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It is not recommended to correct the pH. The best approach is to compare uncorrected ABG values with normal values at 37°C.
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An uncorrected pH at 7.4 and pCO2 at 40 mm Hg reflect acid-base balance.
Many hypothermic patients are volume contracted because of cold diuresis. As a result, hematocrit level may be deceptively high. Hematocrit levels may increase 2% for each 1°C drop in core temperature.
Hypothermia may present with wide fluctuations in electrolytes, and no clear trend or predictability exists as to when a patient's electrolytes will be abnormal or how large swings may be. Plasma potassium levels can be useful in evaluating prognosis. A level of 10 mmol/L or greater is associated with a very low likelihood of recovery. Classic ECG changes of hyperkalemia may be absent or diminished. Chronic hypothermia occasionally can lead to hypokalemia.
Acute hypothermia can result in hyperglycemia, while chronic hypothermia or secondary hypothermia may present with low blood glucose level.
The body's coagulation mechanism is often disrupted in moderate or severe hypothermia, and a disseminated intervascular coagulation–type syndrome can be present.
Coagulopathy has several causes. The primary issue is disruption of enzymatic reactions of the clotting cascade caused by protein denaturization at decreased temperature.
Because the kinetic tests of coagulation are performed at 37°C in the laboratory, a clinically evident coagulopathy may not be reflected by deceptively normal laboratory values.
Imaging Studies
A chest radiograph is indicated in patients with hypoxia. Aspiration pneumonia and pulmonary edema are common findings.
Patients with trauma or altered mental status of indeterminate cause may need a noncontrast head CT scan and further imaging for a standard trauma evaluation.
Other Tests
The ECG may show prolonged PR, QRS, and QT intervals, and atrial or ventricular arrhythmias. The length and height of the respective QT-interval prolongation and characteristic J (Osborne) waves are often proportional to the degree of hypothermia.
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Osborne (J) waves (V3) in a patient with a rectal core temperature of 26.7°C (80.1°F). ECG courtesy of Heather Murphy-Lavoie of Charity Hospital, New Orleans.
