On admission, the diagnosis of hypothermia should be confirmed using a thermometer suitable for measuring very low temperatures. Rectal, esophageal, central venous, or tympanic probes are used to measure central or core temperature. The rectal temperature is usually 1 °C below the esophageal temperature because of the proximity of the great veins draining cold blood from the legs. This difference is reduced if the probe is inserted sufficiently deeply (10-15 cm) into the rectum. This is the most common site of measurement. A probe can be inserted into the esophagus, at the level of the right atrium, but may be influenced by warmed inhaled air, particularly during mechanical ventilation. The tympanic temperature should reflect central nervous system temperature; however, not all parts of the brain are of uniform temperature, with the scalp exposed and the external ear sometimes filled with snow. The temperature can also be measured in the urinary bladder using a Foley catheter or in central venous blood. It is recommended that the temperature is recorded simultaneously at two different sites and continuously monitored in order to follow therapy.
A 12-lead ECG should be recorded, followed by continuous monitoring. Vital signs including pulse, respiratory rate, blood pressure, pupil size and reflexes, consciousness, and neurological deficits should be documented. Unilateral or focal neurological deficits should raise suspicion of a subdural hematoma, cerebral hemorrhage, or stroke. Hypoglycemia, sepsis, and drug or alcohol intoxication may also lead to accidental hypothermia and should be investigated.
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