Accidental hypothermia is an unintentional decline in core temperature below 35°C (95°F). Presentation may be obvious or subtle, especially in urban settings. Symptoms vary from vague complaints to altered levels of consciousness. Physical findings include progressive abnormalities of every organ system. Following initial tachycardia, there is progressive bradycardia (50% decrease in heart rate at 28°C [82.4°F]) with decline in blood pressure and cardiac output. Electrocardiogram (ECG) intervals are prolonged, beginning with the PR interval followed by the QRS interval and finally the QT interval. A J wave (Osborn wave; hypothermic “hump”) may be seen, but is neither pathognomonic nor prognostic. The J wave is present at the junction of the QRS complex and the ST segment. J waves may also be associated with central nervous system lesions, focal cardiac ischemia, young age, and sepsis. In mildly hypothermic patients, an invisible increase in preshivering muscle tone may obscure P waves.
Management and Disposition
Core temperature measurement is best made with an esophageal probe inserted into the lower third of the esophagus. Rectal temperature is less accurate and requires the use of a special low-reading thermometer. Gentle handling and appropriate warming methods are the mainstays of emergency department (ED) treatment. Cardiovascular instability often complicates rewarming; Advanced Cardiac Life Support (ACLS) guidelines for hypothermia provide guidance. If not obvious, a precipitating cause such as hypothyroidism, hypoglycemia, or sepsis should be sought, as should associated pathology. Most patients require admission for observation or to treat associated injuries or comorbidities.
The most common problem with the misdiagnosis of hypothermia in the ED stems from incomplete vital sign data.
Accurate core temperatures, preferably by esophageal probe, and continuous cardiac monitoring are crucial to appropriate management.
Atrial arrhythmias are generally benign and should not be treated. They generally resolve with rewarming.
Most cardiovascular drugs are inactive during hypothermia and should be given only after the body temperature is above 35°C (95°F).
J Waves. This patient’s core temperature was 25.5°C. J waves occur below 32°C, especially in leads II and V6. Below 25°C, they are larger and most common in precordial leads (especially V3 and V4). They are usually upright in aVL, aVF, and left precordial leads (see also Fig. 23.45A, Hypothermia with Osborne Waves [“J” Waves] Present). (Photo contributor: Alan B. Storrow, MD.)