What is the definition of fever for inpatients?

Definition of Fever in Inpatient Settings

According to the Society of Critical Care Medicine and the Infectious Diseases Society of America guidelines, fever in inpatients is defined as a single temperature measurement greater than or equal to 38.3°C (101°F). 1

Temperature Measurement Methods

The most accurate temperature measurements come from central methods:

1. First-line (when available):

   • Pulmonary artery catheter thermistors
   • Bladder catheter thermistors
   • Esophageal balloon thermistors

2. Second-line (when central methods unavailable):

   • Oral temperature measurement (for alert, cooperative patients)
   • Rectal temperature measurement

3. Methods to avoid:

   • Axillary measurements (consistently lower than core temperature)
   • Tympanic membrane infrared devices (poor agreement with core temperature)
   • Chemical dot thermometers (less reliable)

The guidelines specifically recommend against axillary temperature measurements due to significant limitations, with temperatures consistently lower than rectal or oral temperatures by approximately 0.5-1.0°C 2.

Population-Specific Fever Definitions

Different patient populations may have different fever thresholds:

1. ICU patients:

   • ≥38.3°C (101°F) single measurement 1

2. Neutropenic patients:

   • ≥38.3°C (101°F) single oral temperature OR
   • ≥38.0°C (100.4°F) sustained over at least 1 hour 1

3. Elderly patients in long-term care:

   • 37.8°C (100.0°F) single oral temperature OR

   • 37.2°C (99.0°F) repeated oral measurements OR

   • 37.5°C (99.5°F) repeated rectal measurements OR

   • Increase from baseline >1.1°C (2.0°F) 1

4. Hospital-acquired infections (CDC definition):

   • 38°C (100.4°F) 1

Clinical Considerations

• Normal body temperature is generally considered to be 37.0°C (98.6°F), but varies by 0.5-1.0°C according to circadian rhythm and menstrual cycle 1.

• Environmental factors in ICU settings can alter temperature readings, including specialized mattresses, hot lights, air conditioning, cardiopulmonary bypass, peritoneal lavage, dialysis, and continuous hemofiltration 1.

• A substantial proportion of infected patients may not present with fever and may be euthermic or hypothermic. This is particularly common in:

  • Elderly patients
  • Patients with open abdominal wounds
  • Patients with large burns
  • Patients on extracorporeal membrane oxygenation or continuous renal replacement therapy
  • Patients with heart failure, end-stage liver disease, or chronic renal failure
  • Patients taking anti-inflammatory or antipyretic drugs 1

• The absence of fever in patients with infection is associated with worse outcomes 1, 2.

Pitfalls to Avoid

1. Relying on axillary temperature: This method consistently underestimates core temperature and should not be used when accurate temperature measurement is critical.

2. Ignoring non-febrile infections: Remember that absence of fever does not rule out serious infection, particularly in elderly or immunocompromised patients.

3. Confusing fever with hyperthermia: Fever is a regulated increase in body temperature due to cytokine-mediated reset of the hypothalamic set point, while hyperthermia represents unregulated heat production or decreased heat dissipation 3.

4. Overlooking non-infectious causes: About half of fevers in ICU patients are due to non-infectious causes such as deep venous thrombosis, drug reactions, or neuroleptic malignant syndrome 3, 4.

By following these evidence-based definitions and measurement techniques, clinicians can more accurately identify and respond to fever in inpatient settings.