Assessment of the Value of Comorbidity Indices for Risk Adjustment in Colorectal Surgery Patients

Abstract

Background and Purpose Comorbidity indices (CIs) are widely used in retrospective studies. We investigated the value of commonly used CIs in risk adjustment for postoperative complications after colorectal surgery. Methods Patients undergoing colectomy without stoma for colonic neoplasia at a single institution from 2009 to 2014 were included. Four CIs were calculated or obtained for each patient, using administrative data: Charlson-Deyo (CCI-D), Charlson-Romano (CCI-R), Elixhauser Comorbidity Score, and American Society of Anesthesiologists classification. Outcomes of interest in the 90-day postoperative period were any surgical complication, surgical site infection (SSI), Clavien-Dindo (CD) grade 3 or higher complication, anastomotic leak or abscess, and nonroutine discharge. Base models were created for each outcome based on significant bivariate associations. Logistic regression models were constructed for each outcome using base models alone, and each index as an additional covariate. Models were also compared using the DeLong and Clarke-Pearson method for receiver operating characteristic (ROC) curves, with the CCI-D as the reference. Results Overall, 1813 patients were included. Postoperative complications were reported in 756 (42%) patients. Only 9% of patients had a CD grade 3 or higher complication, and 22.8% of patients developed an SSI. Multivariable modeling showed equivalent performance of the base model and the base model augmented by the CIs for all outcomes. The ROC curves for the four indices were also similar. Conclusions The inclusion of CIs added little to the base models, and all CIs performed similarly well. Our study suggests that CIs do not adequately risk-adjust for complications after colorectal surgery.