Comparative Predictive Accuracy of ASA, POSSUM, and NSQIP Risk Scoring Systems in Major Abdominal Surgeries: A Systematic Review

Abstract

This systematic review evaluates and compares the predictive accuracy of three commonly used surgical risk scoring systems in the context of major abdominal surgeries: American Society of Anesthesiologists (ASA) score, Physiological and Operative Severity Score for the enUmeration of Mortality and Morbidity (POSSUM), including its variants, and American College of Surgeons National Surgical Quality Improvement Program (NSQIP) calculator. A comprehensive literature search was conducted across multiple databases, identifying 10 eligible studies that assessed these models in various surgical settings, including elective colorectal resections, emergency laparotomies, and IBD-related procedures. The findings revealed that NSQIP-based models, especially those incorporating frailty indices, demonstrated better calibration and discrimination in elective surgeries. POSSUM and P-POSSUM provided moderate to high predictive accuracy in emergency settings, though they frequently overestimated mortality, particularly in laparoscopic cases. The ASA score, while simple and widely used, showed moderate predictive value but limited precision in complex or high-risk scenarios. Significant heterogeneity in study design, population characteristics, and outcome reporting precluded meta-analysis. However, narrative synthesis confirmed that the performance of each scoring system is context-dependent and that no single model demonstrated consistent superiority across all surgical types. These results underscore the importance of tailored risk assessment strategies and highlight the need for recalibration, external validation, and integration of newer predictive variables in surgical risk modeling.