NPPB and malnutrition: To further confirm that potential confounding variables do not substantially interfere with the model’s core conclusions, we conducted additional stratified analyses based on two factors that were excluded from the final model but may correlate with prognosis: “presence of concurrent pneumonia” and “WAZ < −2 (severe malnutrition).” After stratification, the direction and magnitude of hazard ratios (HR) for the five predictive factors in the original model (modified Ross classification, NT-proBNP, BUN, shock, and thoracotomy) remained stable without significant changes.