Three Risk Stratification Tools and Postoperative Pneumonia After Noncardiothoracic Surgery

BACKGROUND: Postoperative in-hospital pneumonia is a serious complication. This study aims to investigate the association between 3 preoperative stratification tools (American Society of Anesthesiologists Physical Status [ASA-PS] score, Charlson Comorbidity Index [CCI], and Rockwood Frailty Deficit Index [FI]) and risk for postoperative pneumonia. METHODS: We identified adult patients who developed postoperative pneumonia following noncardiothoracic surgery under general anesthesia, between January 1, 2016 and December 31, 2017. Patients with postoperative pneumonia were 1:1 matched to control subjects based on age, sex, and the exact type of operations. Medical records were reviewed to identify variables that may be associated with risk for developing postoperative pneumonia. Analyses adjusted for clinical characteristics were performed using the conditional logistic regression, taking into account 1:1 matched set case-control study design. RESULTS: We identified 211 cases of postoperative pneumonia, and all 3 tested stratification tools were associated with increased risk: ASA-PS (after all adjustments of American Society of Anesthesiologists (ASA) III, odds ratio 4.17 [95% confidence interval 1.74-10.01]; ASA > III 24.03 [6.54-88.32]), CCI (CCI values > 3, 1.29 [1.02-1.63] per unit CCI score), and frail FI score 3.25 (1.45-7.27). Because of incomplete intake documentation, the FI could not be calculated in 57 (13.5%) patients, but these "unknown frailty" patients were also at increased risk for postoperative pneumonia, 3.15 (1.29-7.72). DISCUSSION: Three commonly used stratification indices (ASA-PS score, CCI, and FI) were associated with increased risk for postoperative pneumonia. Patients unable to complete intake form to calculate the FI were also at increased risk.