Fever in the intensive care unit (ICU) patient is a common problem that results in the performance of many diagnostics tests. This increases both the costs of medical care and the exposure of the patient to uncomfortable procedures. The astute clinician will recognize that although a common cause of fever in the ICU is infection, many cases of fever are caused by noninfectious etiologies. Proper management demands implementing a simultaneous algorithm for the workup of noninfectious causes.

Fever is thought to be a protective mechanism against infection. Many animal species are known to develop fever in response to a microbiologic organism. In humans, fever is thought to enhance several parameters of immune function and potentially enhance survival. In addition, hyperthermia also increases cardiac output, oxygen consumption, carbon dioxide production, and energy expenditure, which may be harmful to patients with low cardiopulmonary reserve or cere-brovascular injury. Maternal fever may also be a cause of fetal malformations or spontaneous abortions.

Normal body temperature is 37.0°C with circadian variation of between 0.5°C and 1.0°C. Several methods are used to measure body temperature. Taking the pulmonary artery mixed venous temperature is the most accurate method for measuring core body temperature. Infrared ear thermometry is nearly equivalent to taking pulmonary artery and brain temperatures. Rectal temperatures obtained with a mercury thermometer or electronic probe are often a few tenths of a degree higher than core body temperature. Oral temperatures can be influenced by drinking and eating or warmed air in ventilator circuits. Axillary measurements are unreliable. The Society of Critical Care Medicine defines a fever as a temperature greater than 38.3°C. Most infectious causes of fever follow a diurnal pattern.