Amoxicillin-clavulanic acid resistance in the first postoperative pneumonia after cardiac surgery: risk factors and outcomes from a 10-year cohort analysis.

Abstract

Background: Postoperative pneumonia (POP) is a severe complication after cardiac surgery (CS). A high prevalence of resistant pathogens has been reported. We aimed to identify risk factors and assess the impact on clinical outcomes of POP caused by amoxicillin-clavulanic acid-resistant bacteria (AMC-R POP).

Methods: This single-center retrospective cohort study included patients who underwent CS between January 2013 and December 2023 and developed microbiologically documented POP within 7 postoperative days. Clinical characteristics were compared in univariate and multivariate analyses according to AMC susceptibility of causative bacteria. The primary objective was to study the association between AMC-R POP and intensive care unit (ICU) length of stay.

Results: Among 352 cases of POP, 186 (53%) were AMC-R. The most common AMC-resistant pathogens were AmpC-producing Enterobacterales (25.6%) and Pseudomonas aeruginosa (14.6%). AMC-R POP was independently associated with longer ICU length of stay (adjusted mean difference of 7.0 (95% CI 2.8; 11.7) days). Patients with AMC-R POP had lower 90-days survival in time-to-event analysis (HR 0.50, 95% CI 0.27; 0.93). Independent risk factors of AMC-R POP included redo surgery (adjusted OR 3.74, 95% CI 1.73; 8.84), multiple major procedures (aOR 1.94, 95% CI 1.18; 3.21), and SAPS II ≥ 35 at ICU admission (aOR 2.42, 95% CI 1.50; 3.91).

Conclusion: AMC-R POP represented half of the POP cases occurring within 7 days of CS and was associated with longer ICU length of stay. Patients on redo surgery, particularly those fulfilling other independent risk factors, should be considered to receive empirical antibiotics accordingly in case of suspected POP.