Comparison of 6-min walk test distance vs. estimated maximum oxygen consumption for predicting postoperative pulmonary complications in patients undergoing upper abdominal surgery: a prospective cohort study

Abstract

Abstract Objective The present study aims to evaluate the predictive ability of estimated maximum oxygen consumption (e$$\dot{V}$$ V ˙ O2max) and 6-min walk distance (6MWD) for postoperative pulmonary complications (PPCs) in adult surgical patients undergoing major upper abdominal surgery. Method This study was conducted by collecting data prospectively from a single center. The two predictive variables in the study were defined as 6MWD and e$$\dot{V}$$ V ˙ O2max. Patients scheduled for elective major upper abdominal surgery from March 2019 to May 2021 were included. The 6MWD was measured for all patients before surgery. e$$\dot{V}$$ V ˙ O2max was calculated using the regression model of Burr, which uses 6MWD, age, gender, weight, and resting heart rate (HR) to predict aerobic fitness. The patients were categorized into PPC and non-PPC group. The sensitivity, specificity, and optimum cutoff values for 6MWD and e$$\dot{V}$$ V ˙ O2max were calculated to predict PPCs. The area under the receiver operating characteristic curve (AUC) of 6MWD or e$$\dot{V}$$ V ˙ O2max was constructed and compared using the Z test. The primary outcome measure was the AUC of 6MWD and e$$\dot{V}$$ V ˙ O2max in predicting PPCs. In addition, the net reclassification index (NRI) was calculated to assess ability of e$$\dot{V}$$ V ˙ O2max compared with 6MWT in predicting PPCs. Results A total of 308 patients were included 71/308 developed PPCs. Patients unable to complete the 6-min walk test (6MWT) due to contraindications or restrictions, or those taking beta-blockers, were excluded. The optimum cutoff point for 6MWD in predicting PPCs was 372.5 m with a sensitivity of 63.4% and specificity of 79.3%. The optimum cutoff point for e$$\dot{V}$$ V ˙ O2max was 30.8 ml/kg/min with a sensitivity of 91.6% and specificity of 79.3%. The AUC for 6MWD in predicting PPCs was 0.758 (95% confidence interval (CI): 0.694–0.822), and the AUC for e$$\dot{V}$$ V ˙ O2max was 0.912 (95%CI: 0.875–0.949). A significantly increased AUC was observed in e$$\dot{V}$$ V ˙ O2max compared to 6MWD in predicting PPCs (P < 0.001, Z = 4.713). And compared with 6MWT, the NRI of e$$\dot{V}$$ V ˙ O2max was 0.272 (95%CI: 0.130, 0.406). Conclusion The results suggested that e$$\dot{V}$$ V ˙ O2max calculated from the 6MWT is a better predictor of PPCs than 6MWD in patients undergoing upper abdominal surgery and can be used as a tool to screen patients at risk of PPCs.