Frailty Predicts 30-day Mortality in Spine Surgery Patients Classified as Obese and the Risk Analysis Index Exhibits Excellent Discrimination

Abstract Background/Objectives Obesity is a global health challenge that affects > 1/3 adults worldwide. Obesity and frailty pose considerable health risks due to their potential to interact and amplify one another’s negative effects. Therefore, we sought to compare the discriminatory thresholds and independent relationship of the risk analysis index (RAI), 5-factor modified frailty index (m-FI-5) and greater patient age for the primary endpoint of 30-day postoperative mortality. Subjects/Methods We included spine surgery patients ≥ 18 years old, from the American College of Surgeons National Quality Improvement program database from 2012-2020, that were classified as obese. We performed receiver operating characteristic curve analysis to compare the discrimination threshold of RAI, mFI-5, and patient age for 30-day postoperative mortality. Risk-adjusted analyses were performed. Results Overall, there were 149 163 patients evaluated, and in the ROC analysis for 30-day postoperative mortality, RAI showed superior discrimination C-statistic 0.793 (95% CI: 0.773-0.813), compared to mFI-5 C-statistic 0.671 (95% CI 0.650-0.691), and patient age C-statistic 0.686 (95% CI 0.666-0.707). By subgroups for obesity class I-III, consistent results were observed (C-statistics range: RAI 0.767-0.808; mFI-5 0.642-0.693; patient age 0.665-0.706). In the risk-adjusted analyses, frailty had a dose-dependent relationship with 30-day postoperative mortality, and the RAI had a larger effect size (p<0.001). Additionally, obesity and frailty had a synergistic dose-dependent relationship across obesity class I-III (p<0.001). Conclusion In this study of 149 163 patients classified as obese and undergoing spine procedures in an international prospective surgical database, the RAI demonstrated superior discrimination compared to the mFI-5 and patient age in predicting 30-day postoperative mortality risk. The deleterious effects of frailty and obesity were synergistic as their combined effect predicted worse outcomes.