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  • Up to 70% of intensive care unit (ICU) patients will develop fever.

  • Fever is a physiologic response where the body attempts to raise the thermoregulatory set point, whereas hyperthermia is a nonphysiologic disruption of thermoregulation.

  • Approximately 50% of fevers are due to noninfectious causes, such as drug fevers, surgical trauma, and central nervous system injury.

  • A thoughtful evaluation of a fever may reduce costs and lessen the potential risk to the patient.

  • Although fever is associated with adverse outcomes in the ICU, there is no conclusive evidence to support the routine treatment of infectious fevers in nonbrain-injured patients.

  • Extreme elevations of temperature (>41.1°C) in adults are most often due to noninfectious etiologies.

  • Heat stroke, serotonin syndrome, neuroleptic malignant syndrome, and malignant hyperthermia are life-threatening causes of hyperthermia that must be immediately recognized and treated in order to avoid multisystem organ failure and death.


Elevations in body temperature are very common in the intensive care unit (ICU).1 Fever is the term used to describe a physiologic increase in the natural set-point for homeostatic temperature control while hyperthermia refers to an uncontrolled elevation of body temperature. Although fever is a natural response to illness and injury, the occurrence of an elevated temperature in a critically ill patient frequently initiates a gamut of unfocused diagnostic testing and multiple intravenous infusions of broad-spectrum antibiotics, often without a critical appraisal of the unique issues of the individual patient. This “one size fits all” approach may not only add unnecessary costs, manpower, and interventions to patient care, but may also expose patients to unnecessary risks. In selected patients, clinical pathways have the potential both to reduce costs and to improve the appropriateness of treatment, the latter of which may then lead to improved survival. A thorough understanding of the common etiologies of fever is critical to customizing the care of individual patients. In this chapter, we will review the physiology of temperature regulation, how to best measure temperature in the ICU, the epidemiology and the clinical impact of fever, how to differentiate fever from hyperthermia, common infectious and noninfectious causes of fever, and general guidelines to evaluate and manage febrile patients in the ICU.


The thermoregulation is the responsibility of the hypothalamus.2 Healthy, nonfasting, resting adults closely regulate sublingual temperature between 33.2°C and 38.1°C.3 There is normally a small diurnal variation in temperature of approximately 0.5°C which nadirs around 6 a.m. and peaks around 4 p.m.4 This tight regulation occurs due to continual adjustment of thermogenic and cooling processes. Eating, exercise, and sleep deprivation increase body temperature while fasting reduces it.5 Among menstruating women, core body temperature rises approximately 0.3°C degree after ovulation during the luteal phase of the cycle.6 Circadian peak and nadir temperatures are similar between the young and healthy elderly persons.7


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