Blood Cultures in Ventilated Seizure Patients with New Fever
Yes, blood cultures should be obtained in a ventilator-dependent patient who develops new fever, regardless of the seizure history. The seizure itself does not change the fundamental approach to fever evaluation in critically ill patients.
Primary Recommendation
Obtain at least two sets of blood cultures (ideally 60 mL total blood volume) collected sequentially from different anatomical sites without time intervals between them 1. This is a best-practice statement from the most recent 2023 Society of Critical Care Medicine and Infectious Diseases Society of America guidelines for evaluating new fever in ICU patients 1.
Rationale for Blood Cultures in This Clinical Scenario
Ventilated patients are at high risk for serious infections including ventilator-associated pneumonia, catheter-related bloodstream infections, and other nosocomial infections that can cause bacteremia with significant morbidity and mortality 1.
New fever in the ICU warrants comprehensive evaluation to identify potentially life-threatening infections early, as delayed or inadequate antimicrobial therapy is independently associated with increased mortality 2.
Blood cultures remain the most sensitive method for detecting bacteremia and are essential for guiding appropriate antimicrobial therapy and improving outcomes 3, 4, 5.
Proper Collection Technique
If the patient has a central venous catheter (which is common in ventilated patients):
- Collect one blood culture set from peripheral venipuncture 1
- Collect at least one set through the catheter, sampling at least two lumens 1
- This allows calculation of differential time to positivity to help identify catheter-related bloodstream infection 1
Collection standards:
- Each set should include aerobic and anaerobic bottles with 10 mL per bottle (20-30 mL per set) 1
- Use 2% chlorhexidine gluconate in 70% isopropyl alcohol for skin preparation (30 seconds drying time) 1
- Draw cultures before initiating new antimicrobial therapy whenever possible, but do not delay antibiotics more than 45 minutes in septic patients 1, 2
Additional Fever Workup Components
Beyond blood cultures, the comprehensive fever evaluation should include:
Chest radiograph to evaluate for pneumonia, which is the second most common cause of ICU-acquired infection and ubiquitous in mechanically ventilated patients 1
Respiratory viral testing if pneumonia is suspected or new respiratory symptoms develop, using viral nucleic acid amplification test panels 1
Daily assessment of all intravascular devices for signs of infection at insertion sites 1
Urinalysis and urine culture if urinary catheter is present and urinary tract infection is suspected 1
Important Caveats
The seizure itself is not a contraindication or reason to defer blood cultures. While seizures can occasionally cause transient fever through increased metabolic activity, in a ventilated ICU patient, new fever must be assumed infectious until proven otherwise given the high-risk environment and potential for rapid deterioration 1.
Common pitfall to avoid: Do not attribute the fever solely to the seizure without ruling out infection. Critically ill patients have multiple risk factors for serious infections (invasive devices, immunosuppression, prolonged hospitalization), and missing bacteremia can lead to septic shock and death 1, 3.
Timing considerations: Obtain blood cultures within the first 24 hours of fever onset 1. If the patient is already on antibiotics, cultures should still be obtained as they may reveal inadequate antimicrobial coverage or resistant organisms, though yield will be reduced 3.
Evidence Quality Note
The 2023 guidelines 1 represent the most current expert consensus and supersede the 2008 recommendations 1, though the core principles remain consistent. The recommendation for blood cultures in febrile ICU patients is a best-practice statement reflecting strong expert consensus despite the inherent difficulty in conducting randomized trials for diagnostic testing in critically ill populations.