What is the approach to evaluating a patient with a known fever (pyrexia)?

From the Guidelines

The workup of a known fever in adult patients in the ICU should begin with central temperature monitoring methods, such as thermistors for pulmonary artery catheters, bladder catheters, or esophageal balloon thermistors, and a thorough physical examination to identify potential sources of infection, as recommended by the Society of Critical Care Medicine and the Infectious Diseases Society of America guidelines 1. When evaluating a new fever in adult patients in the ICU, it is essential to consider the patient's clinical presentation, medical history, and recent procedures or surgeries.

• The initial workup should include a chest radiograph, as recommended by the guidelines 1.
• For patients who have recently undergone thoracic, abdominal, or pelvic surgery, a CT scan should be performed in collaboration with the surgical service if an etiology is not readily identified by initial workup 1.
• Laboratory tests, such as complete blood count with differential, comprehensive metabolic panel, urinalysis, and blood cultures, should be obtained to help identify the underlying cause of the fever.
• The use of antipyretic medications, such as acetaminophen or ibuprofen, should be considered for patients who value comfort by reducing temperature, but not as a routine measure to reduce fever 1.
• For patients with fever and no abdominal signs or symptoms or liver function abnormalities, and no recent abdominal surgery, routine abdominal ultrasound or point-of-care ultrasound (POCUS) is not recommended as an initial investigation 1.
• In patients with fever and recent abdominal surgery or abdominal symptoms, a formal bedside diagnostic ultrasound of the abdomen is recommended 1.
• Blood cultures should be collected from at least two different anatomical sites, and simultaneous collection of central venous catheter and peripherally drawn blood cultures should be performed to allow calculation of differential time to positivity 1.

From the Research

Approach to Working Up a Known Fever

• The first step in working up a known fever is a complete assessment, including a thorough physical assessment and an evaluation of the history of present illness as well as a detailed review of all the patient's medications 2.
• Infection should always be a primary consideration for the cause of a fever, and evaluating each body system can match symptoms with a possible cause for fever 2.
• Noninfectious causes of fever need to be included in the differential diagnostic process 2, 3.
• Adjunctive testing, including C-reactive protein, erythrocyte sedimentation rate, and procalcitonin, has been evaluated in the literature, but these tests do not have the needed sensitivity and specificity to definitively rule in a bacterial cause of fever 3.

Diagnostic Tools

• Total body computerized tomography (TBCT) is frequently used as a diagnostic tool for fever of unknown origin (FUO) workup, and it has a clinically significant yield under specific clinical scenarios in medical patients with FUO 4.
• TBCT has a yield of 55% in patients with an elevated CRP, low hemoglobin, and high leucocyte count 4.
• Blood cultures should be obtained in septic shock or if the results will change clinical management 3.

Clinical Evaluation

• A new fever in an adult patient in the ICU should trigger a careful clinical assessment rather than automatic orders for laboratory and radiological tests 5.
• A cost-conscious approach to obtaining diagnostic studies should be undertaken if they are indicated after a clinical evaluation 5.
• The goal of such an approach is to determine, in a directed manner, whether infection is present so that additional testing can be avoided and therapeutic options can be identified 5.

Considerations

• Fever may not be always present in true infection, especially in elderly and immunocompromised patients 3.
• Oral temperatures suffer from poor sensitivity to diagnose fever, and core temperatures should be utilized if concern for fever is present 3.
• Consideration of non-infectious causes of elevated temperature is needed based on the clinical situation 3.