Fever is a common abnormality in the intensive care unit (ICU), which prompts important diagnostic and treatment decisions. The definition, differential diagnosis, diagnostic evaluation, and management of fever in the ICU are reviewed here. The pathophysiology of fever is discussed separately. (See "Pathophysiology and treatment of fever in adults".)
Normal body temperature is approximately 37.0ºC (98.6ºF), although this varies with the time of day and the method of measurement used. The definition of fever is arbitrary; as the temperature that defines fever is lowered, its sensitivity increases and its specificity decreases. A joint task force from the American College of Critical Care Medicine and the Infectious Diseases Society of America defined fever as a body temperature of 38.3ºC (101ºF) or higher . We adhere to this definition in this review because it is widely accepted. It is reasonable to use a lower temperature to define fever in immunocompromised patients.
Conventional means of measuring temperature in the ICU include intravascular, intravesicular (ie, bladder), rectal, and oral [1-6]. The gold standard is the thermistor on a pulmonary artery catheter, although these are used infrequently and may give unreliable temperature readings if the catheter is used to rapidly administer volume . Regardless of which method is chosen, the same method and site of measurement should be used repeatedly to facilitate the trending of serial measurements. Alternative methods, such as axillary, temporal artery, tympanic, and chemical dot monitors, should not be used because they are inaccurate during critical illness [1,6-12].
Fever complicates up to 70 percent of all ICU admissions and is often due to an infection or another serious condition [13,14]. In one observational study of 24,204 adult ICU admissions, fever ≥39.5ºC (103ºF) was associated with an increase in mortality (20 versus 12 percent) . Fever has also been associated with an increased length of stay, increased cost of care, and poorer outcomes in patients with traumatic head injury, subarachnoid hemorrhage, or pancreatitis [13,15-21]. The same associations probably exist with other conditions that have not been studied. Fever may prompt unnecessary investigations and lead to inappropriate antibiotic use.
The importance of fever as a pathophysiological process is poorly understood. Although regarded as a sign of clinical deterioration, fever can be an appropriate adaptive response to infection. For example, one study showed that elevated peak temperatures in ICU patients with infections were associated with decreased hospital mortality . Compared to patients with peak temperatures 36.5 to 36.9ºC, patients with peak temperatures 39 to 39.4oC had significantly lower hospital mortality (OR, 0.56; 95% CI 0.48 to 0.66). However, in non-infectious cases of fever, mortality increased with rising temperature (OR, 2.07; 95% CI 1.68 to 2.55).