The Impact of Preoperative Functional Capacity on Postoperative Mortality and Morbidity. A Prospective Cohort Study

Background: Functional capacity is an important determinant of surgical risk, yet the relationship between self-reported metabolic equivalents of task (MET) levels, treated as a multi-level variable, and postoperative outcomes remains unclear. This study evaluated the association between categorized MET levels and short- and long-term mortality and morbidity. Methods: This dual-center prospective cohort study enrolled adults undergoing elective non-cardiac surgery at Karolinska University Hospital (Solna and Huddinge) between 2020–2023, excluding obstetric, transplant, day surgery, and non-operative cases. Preoperative functional capacity was assessed in MET categories (1, 2–3, 4–5, 6–8, ≥9). Primary outcomes were all-cause mortality at 30 and 365 days; secondary outcomes were DAH30 and DAH365. Analysis used Accelerated Failure Time models and logistic quantile regression. Results: In total, 38,293 patients were included. The incidence of 30- and 365-day mortality was 220 (0.6%) and 2061 (5.4%), respectively. In the 365-day mortality analysis, adjusted AFT models showed progressively shorter relative median survival times with decreasing MET levels compared to MET ≥ 9: 0.75 (0.56–0.98) for MET 6–8, 0.52 (0.40–0.68) for MET 4–5, 0.39 (0.29–0.51) for MET 2–3, and 0.24 (0.16–0.34) for MET 1. The adjusted marginal absolute risk difference in 365-day mortality was distinct across all MET categories: 0.8% (95% CI: 0.1 to 1.5) for MET 6–8, 2.3% (1.6 to 2.90) for MET 4–5, 3.8% (2.91 to 4.6) for MET 2–3, and 7.2% (5.2 to 9.8) for MET 1. Lower MET levels were also associated with fewer days alive and at home at 365 days (DAH365), particularly in the lower quantiles. Conclusions: Self-reported functional capacity, categorized by MET levels, is associated with both short- and long-term postoperative mortality and morbidity in a dose-response-like manner. These findings support continued use of MET in preoperative assessments and suggest that granular MET categorization enhances risk stratification.