Derivation and validation of a preoperative risk model for postoperative mortality (SAMPE model): An approach to care stratification

Luciana Cadore Stefani, Claudia De Souza Gutierrez, Stela Maris de Jezus Castro, Rafael Leal Zimmer, Felipe Polgati Diehl, Leonardo Elman Meyer, Wolnei Caumo, Luciana Cadore Stefani, Claudia De Souza Gutierrez, Stela Maris de Jezus Castro, Rafael Leal Zimmer, Felipe Polgati Diehl, Leonardo Elman Meyer, Wolnei Caumo

Abstract

Ascertaining which patients are at highest risk of poor postoperative outcomes could improve care and enhance safety. This study aimed to construct and validate a propensity index for 30-day postoperative mortality. A retrospective cohort study was conducted at Hospital de Clínicas de Porto Alegre, Brazil, over a period of 3 years. A dataset of 13524 patients was used to develop the model and another dataset of 7254 was used to validate it. The primary outcome was 30-day in-hospital mortality. Overall mortality in the development dataset was 2.31% [n = 311; 95% confidence interval: 2.06-2.56%]. Four variables were significantly associated with outcome: age, ASA class, nature of surgery (urgent/emergency vs elective), and surgical severity (major/intermediate/minor). The index with this set of variables to predict mortality in the validation sample (n = 7253) gave an AUROC = 0.9137, 85.2% sensitivity, and 81.7% specificity. This sensitivity cut-off yielded four classes of death probability: class I, <2%; class II, 2-5%; class III, 5-10%; class IV, >10%. Model application showed that, amongst patients in risk class IV, the odds of death were approximately fivefold higher (odds ratio 5.43, 95% confidence interval: 2.82-10.46) in those admitted to intensive care after a period on the regular ward than in those sent to the intensive care unit directly after surgery. The SAMPE (Anaesthesia and Perioperative Medicine Service) model accurately predicted 30-day postoperative mortality. This model allows identification of high-risk patients and could be used as a practical tool for care stratification and rational postoperative allocation of critical care resources.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Trial diagram for SAMPE model…
Fig 1. Trial diagram for SAMPE model dataset analysis.
Fig 2. ROC curve calculated using the…
Fig 2. ROC curve calculated using the development SAMPE model dataset compared to the ASA model.
Fig 3. Model calculator developed in the…
Fig 3. Model calculator developed in the Google Docs platform.
Fig 4. Flow of the high-risk patient’s…
Fig 4. Flow of the high-risk patient’s care.

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