Fever in the Intensive Care Patient

Excerpt

Temperature is one of the most important vital signs for all patients, including intensive care units (ICU). Fever or hypothermia often necessitates further physical evaluations, investigations, and changes in treatment in the ICU.

The definition of fever in the ICU is different from the usual definition of fever. Fever in an ICU patient is defined as a single temperature of ≥101 degrees F or ≥38.3 C, as per the American College of Critical Care Medicine (ACCCM) and Infectious Disease Society of America (IDSA) joint task force. Also, the ACCCM and IDSA recommend that fever in ICU should be investigated only if the temperature is ≥101 degrees F. Hyperpyrexia or hyperthermia is a temperature of more than 105.8 degrees F (or 41 degrees C) and is uncommonly encountered in intensive care settings.

In immunocompromised or neutropenic patients, a lower threshold should be considered for fever diagnosis as these patients do not mount an appropriate febrile response. Also, the clinical, laboratory, and radiological manifestations of inflammation/infection would be scanty or absent in these patients, at least in the initial stages. Fever in a neutropenic ICU patient is defined as a single temperature more than 101 F (38.3 C) or a temperature more than 100.4 F (38.0 C) sustained for more than one hour in a patient with an absolute neutrophil count (ANC) less than 500 cells/mm. One also needs to be aware that extracorporeal therapies, including continuous renal replacement therapy or extracorporeal membrane oxygenation, could mask or alter the febrile response.

Fever is expected to provide a protective effect and help the host eliminate the invading organisms. Also, fever is associated with increased mortality and morbidity in ICU patients and forms part of mortality prediction scores, including APACHE II & III. However, studies on fever and mortality in ICU patients have been unequivocal. A large 2008 epidemiological study had shown that a temperature more than ≥ 39.5 degrees C was associated with increased mortality in critically ill patients, and the mere presence of a temperature ≥38.3 degrees C failed to produce any association with mortality. A subsequent study (FACE) published in 2012 reported that higher 28-day mortality observed with temperature more than ≥ 39.5 degrees C occurred in non-septic patients and not in patients with sepsis. Certain studies have also shown an inverse relation between fever and mortality in ICU and emergency patients.

The fever in the ICU could merely be a continued manifestation of the disease/disorder that prompted the ICU admission or could result from certain unique etiologies in the ICU, and very rarely due to the flare-up or manifestation of an underlying dormant disease or disorder. The fever unique to the ICU settings could result from interventions or therapies provided during ICU care or the patient manifesting new-onset fever due to SIRS, septic, metabolic or neuroendocrine response. This review predominantly discusses the fever in non-neutropenic or non-immunocompromised ICU patients. However, clinical and/or management-related overlaps between different patient groups are not unexpected.