External validation of the ARISCAT, Gupta Respiratory Failure, and Gupta Pneumonia risk scores in patients undergoing open abdominal aortic surgery: a single-center retrospective cohort study

Abstract Background. The ARISCAT, Gupta Respiratory Failure, and Gupta Pneumonia scores predict postoperative pulmonary complications, but their validity in open abdominal aortic surgery — a high-risk population — is unestablished. We aimed to externally validate all three scores in this population. Methods. Single-center retrospective cohort study of 693 adults undergoing open abdominal aortic surgery for infrarenal aortic aneurysm and/or peripheral arterial and aortic disease, at a tertiary center in Krakow, Poland, 2015–2023. Discrimination (area under the receiver operating characteristic curve) and calibration (calibration-in-the-large, slope, observed-to-expected ratio, calibration belt) of the three scores were assessed for their respective endpoints — composite pulmonary complication, respiratory failure, and pneumonia. Net clinical benefit was assessed by decision curve analysis, per the TRIPOD + AI 2024 statement. Results. The cohort was predominantly male (85.1%), median age 68 years (interquartile range, 64–73), and high surgical risk (73.0% American Society of Anesthesiologists physical status III). Postoperative pulmonary complication incidence was 19.5% (n = 135), respiratory failure 8.7% (n = 60), and pneumonia 9.1% (n = 63). All three scores showed poor discrimination: ARISCAT area under the receiver operating characteristic curve 0.563 (95% confidence interval, 0.512–0.615), Gupta Respiratory Failure 0.573 (0.516–0.631), Gupta Pneumonia 0.604 (0.536–0.672). All scores systematically underestimated risk (calibration-in-the-large, + 0.426, + 0.369, and + 0.837; observed-to-expected ratios, 1.38, 1.40, and 2.17; calibration belt P < 0.001, P = 0.010, and P < 0.001). Originally proposed cut-offs classified 75%–83% of patients as high-risk. Decision curve analysis showed net benefit over a treat-all strategy only for ARISCAT, within a narrow band near a 20% threshold; the Gupta scores showed no net benefit at any threshold. Conclusions. The ARISCAT, Gupta Respiratory Failure, and Gupta Pneumonia scores provide insufficient pulmonary risk stratification for patients undergoing open abdominal aortic surgery. Systematic underestimation of risk, combined with limited net clinical benefit at their original cut-offs, underscores the need for an aortic-specific pulmonary risk prediction model. Trial registration. Open Science Framework (OSF), https://doi.org/10.17605/OSF.IO/349UR. Registered 9 June 2026.