Should cultures be sent in a patient with fever without hemodynamic instability in the Intensive Care Unit (ICU)?

Blood Cultures in ICU Fever Without Hemodynamic Instability

Yes, blood cultures should be sent for ICU patients with new fever even without hemodynamic instability, as part of a systematic fever workup that includes at least two sets of blood cultures (ideally 60 mL total) collected consecutively from different anatomical sites. 1

Core Recommendation for Blood Culture Collection

The Society of Critical Care Medicine and Infectious Diseases Society of America 2023 guidelines establish blood cultures as a best-practice statement for ICU fever workup, regardless of hemodynamic status. 1 The absence of hemodynamic instability does not exclude serious bacteremia or fungemia that could rapidly progress to septic shock if untreated. 2

Proper Collection Technique

• Collect at least two sets of blood cultures (20-30 mL per set, ideally 60 mL total blood volume) sequentially from different anatomical sites without time intervals between them 1, 3
• If a central venous catheter is present, obtain simultaneous collection from both the catheter (sampling at least two lumens) and peripheral venipuncture to calculate differential time to positivity for catheter-related bloodstream infection diagnosis 1, 2
• All cultures must be obtained within the first 24 hours of fever onset, ideally before initiating antimicrobial therapy 2, 3
• Use 2% chlorhexidine gluconate in 70% isopropyl alcohol for skin preparation with 30 seconds drying time 2

Complete Fever Workup Beyond Blood Cultures

Blood cultures are only one component of the systematic evaluation required for new ICU fever. 1

Mandatory Initial Investigations

• Chest radiograph should be performed on all patients with new ICU fever, as pneumonia is the second most common ICU-acquired infection and ubiquitous in mechanically ventilated patients 1, 2
• Daily examination of all intravascular device insertion sites for inflammation, purulence, or signs of venous thrombosis 1, 2
• Respiratory viral testing using nucleic acid amplification test panels if pneumonia is suspected or new respiratory symptoms develop 1, 2

Conditional Investigations Based on Clinical Context

• Urinalysis and urine culture if urinary catheter present and urinary tract infection suspected, with catheter replacement before obtaining cultures from the newly placed catheter 1, 2
• CT imaging for patients with recent thoracic, abdominal, or pelvic surgery if initial workup does not identify an etiology 1
• Formal abdominal ultrasound for patients with fever and recent abdominal surgery, abdominal symptoms, or abnormal liver function tests 1
• Thoracic bedside ultrasound for patients with abnormal chest radiograph when sufficient expertise available 1

Critical Rationale for Cultures Despite Hemodynamic Stability

The 2023 guidelines emphasize that new fever in ICU patients must be assumed infectious until proven otherwise given the high-risk environment and potential for rapid deterioration. 2 Several factors support obtaining cultures even in stable patients:

• Ventilated and ICU patients are at exceptionally high risk for serious infections including ventilator-associated pneumonia, catheter-related bloodstream infections, and nosocomial bacteremia with significant morbidity and mortality 2
• Delayed or inadequate antimicrobial therapy is independently associated with increased mortality 2
• Hemodynamic stability at presentation does not predict which patients will deteriorate; early identification of pathogens allows targeted therapy before clinical worsening 1, 2
• Blood cultures obtained after antibiotic initiation have reduced yield but may still reveal inadequate coverage or resistant organisms 2

Common Pitfalls to Avoid

• Do not wait for fever spikes or hemodynamic instability before drawing cultures; consecutive/simultaneous collection is as effective as timed intervals for detecting bacteremia 3
• Do not assume non-infectious etiology based solely on hemodynamic stability; up to 75% of fever cases may be non-infectious, but this requires systematic exclusion of infection first 4
• Do not order automatic test panels without clinical assessment; the workup should be guided by targeted examination findings, recent procedures, indwelling devices, and immunocompromising conditions 4
• Do not overlook "silent sources" such as sinusitis, decubitus ulcers, perianal abscesses, or catheter tunnel infections that may not cause hemodynamic compromise initially 4

Non-Infectious Causes to Consider Concurrently

While obtaining cultures, simultaneously evaluate for non-infectious fever etiologies including drug-induced fever (mean onset 21 days after drug initiation), inflammatory conditions (pancreatitis, gout), vascular causes (venous thrombosis, pulmonary infarction), endocrine emergencies (thyroid storm, adrenal insufficiency), and malignancy-related fever. 4 However, this evaluation should occur in parallel with—not instead of—infectious workup. 4, 5