Revised cardiac risk index poorly predicts cardiovascular complications after adhesiolysis for small bowel obstruction

Abstract

Background: The number of patients undergoing preoperative risk stratification in the United States is expected to increase as the population ages. A large percentage of patients undergo some form of preoperative testing, and society guidelines suggest that up to 50% of the testing in lower risk surgical subgroups is unnecessary. The Revised Cardiac Risk Index and the risk calculator of the American College of Surgeons National Surgical Quality Improvement Program are widely used tools as the first step of preoperative cardiac evaluation. The Revised Cardiac Risk Index was developed to fill a need for objective perioperative cardiac risk evaluation. Despite the ease of use of Revised Cardiac Risk Index, it is uncertain if the stratification is accurate for surgical patients because its accuracy in large surgical samples has not been tested. With the National Surgical Quality Improvement Program risk calculator having excellent accuracy in estimating cardiac complications (area under the receiver operating characteristic 0.895), a unique opportunity to test the predictive accuracy of postsurgical cardiac events became available. The purpose of this study is to determine the accuracy of the Revised Cardiac Risk Index for predicting cardiovascular complications after adhesiolysis for small bowel obstruction.

Methods: From 2005 to 2015, 34,032 cases of open or laparoscopic adhesiolysis (Current Procedural Terminology codes 44005 and 44180) for small bowel obstruction (International Classification of Diseases, 10th edition [ICD-10]) were analyzed using the National Surgical Quality Improvement Program dataset. Revised Cardiac Risk Index estimates were calculated for each case and compared to reported cardiovascular complications (myocardial infarction or cardiac arrest) using univariable logistic regression. Overall predictive accuracy was assessed by measuring model discrimination (area under the receiver operating characteristic) and model calibration (Hosmer-Lemeshow chi-squared statistics).

Results: Although the Revised Cardiac Risk Index predicted cardiovascular complications with an odds ratio of 2.3 and a 95% confidence interval of 1.9 to 2.8 (P < .001) and the Hosmer-Lemeshow chi-square was significant (0.22, P = 0.64), the area under the receiver operating characteristic was poor (0.63, 95% confidence interval 0.59-0.67).

Conclusion: Despite its relative simplicity, the Revised Cardiac Risk Index performed poorly as a predictor of cardiovascular complications after adhesiolysis for small bowel obstruction. These findings question the utility of the Revised Cardiac Risk Index in this patient population. Future studies should aim to develop models that are computationally simple while retaining predictive accuracy.