Background: Despite the excellent negative predictive value of sterile respiratory cultures, antibiotics often are continued after negative endotracheal aspirate (ETA) or bronchoalveolar lavage (BAL) for critically ill trauma patients. We hypothesized that persistent elevation of the Clinical Pulmonary Infection Score (CPIS) would predict continued antibiotic therapy after a negative respiratory culture for intubated trauma patients, and that prolonged antibiotics would provide no benefit.
Methods: We performed a four-year retrospective cohort analysis (May 1, 2011-September 30, 2015), including patients from our trauma database with ETA or BAL, excluding patients with any infection other than pneumonia or bacteremia. Cultures with <2+ organisms on gram stain and <2+ or 104 organisms on culture were considered negative. The CPIS was assessed at the time of culture and five days later, when all cultures were final. Multiple logistic regression was used to identify predictors of long-term antibiotic therapy.
Results: A series of 106 patients with negative cultures were included, of whom 61 had ≤5 d of antibiotics and 45 had >5 d of antibiotics. There were no differences in injury severity, head or chest trauma, initial CPIS, or subsequent culture results between the groups. Long-term antibiotic therapy did not affect intensive care unit (ICU) length of stay (LOS), ventilator days, hospital LOS, or death. Factors predicting long-term antibiotic therapy included development of a localized chest radiograph infiltrate (odds ratio [OR] 6.8; 95% confidence interval [CI] 1.7-28), CPIS >5 five days after culture (OR 6.1; 95% CI 1.2-32), and a colonized culture (OR 3.3; 95% CI 1.3-8.3).
Conclusions: Long-term antibiotic therapy for intubated trauma patients with negative respiratory cultures provided no benefit and was predicted by development of a localized chest radiograph infiltrate, persistently elevated CPIS, and a contaminated/colonized culture. Although long-term antibiotic use did not worsen outcomes, better strategies are needed to diagnose pneumonia accurately and ensure timely discontinuation of antibiotics when appropriate.