Risk factors for postoperative pneumonia after cardiac surgery and development of a preoperative risk score*

Abstract

Objectives: The aims of this study were, first, to identify risk factors for microbiology-proven postoperative pneumonia after cardiac surgery and, second, to develop and validate a preoperative scoring system for the risk of postoperative pneumonia.

Design and setting: A single-center cohort study.

Patients: All consecutive patients undergoing cardiac surgery between January 2006 and July 2011.

Interventions: None.

Measurements and main results: Multivariate analysis of risk factors for postoperative pneumonia was performed on data from patients operated between January 2006 and December 2008 (training set). External temporal validation was performed on data from patients operated between January 2009 and July 2011 (validation set). Preoperative variables identified in multivariate analysis of the training set were then used to develop a preoperative scoring system that was validated on the validation set. Postoperative pneumonia occurred in 174 of the 5,582 patients (3.1%; 95% CI, 2.7-3.6). Multivariate analysis identified four risk factors for postoperative pneumonia: age (odds ratio, 1.02; 95% CI, 1.01-1.03), chronic obstructive pulmonary disease (odds ratio, 2.97; 95% CI, 1.8-4.71), preoperative left ventricular ejection fraction (odds ratio, 0.98; 95% CI, 0.96-0.99), and the interaction between RBC transfusion during surgery and duration of cardiopulmonary bypass (odds ratio, 2.98; 95% CI, 1.96-4.54). A 6-point score including the three preoperative variables then defined two risk groups corresponding to postoperative pneumonia rates of 1.8% (score < 3) and 6.5% (score ≥ 3).

Conclusion: Assessing preoperative risk factors for postoperative pneumonia with the proposed scoring system could help to implement a preventive policy in high-risk patients with a risk of postoperative pneumonia greater than 4% (i.e., patients with a score ≥ 3).