A Prospective Observational Study Conducted at a Single Center in Japan to Validate a Previously Developed Predictive Formula of In-Hospital Mortality for Patients Aged ≥65 Years with Endogenous Diseases Transported by Ambulance

BACKGROUND: In 2019, we developed a predictive formula of in-hospital mortality for inpatients aged ≥65 years transported by ambulance for endogenous diseases. In this study, we aimed to validate this previously developed predictive formula. MATERIAL/METHODS: In this single-center prospective observational study, we enrolled all patients aged ≥65 years who were transported by ambulance and admitted to an acute care hospital in Japan for endogenous diseases. We calculated the score according to our developed formula using age, disturbance of consciousness, the shock index, and amount of oxygen administered, with each item scoring 1 point and then totaling them. We subsequently evaluated the in-hospital mortality rate, stratum-specific likelihood ratio, and area under the receiver operating characteristic curve (AUC) of the formula, using in-hospital mortality as the primary outcome. RESULTS: In total, 325 patients were included in this study. Forty-two patients died during hospitalization. Multivariable logistic regression analysis (forced-entry method) revealed that disturbance of consciousness and oxygen administration 5 L/min or more were significantly associated with mortality during hospitalization. In contrast, aged ≥90 years and shock index of 1 or higher were not significant. The mortality and stratum-specific likelihood ratios for scores in the predictive formula of 3 and 4 were 40.9% and 4.66, and 66.7% and 13.48, respectively. The AUC of the predictive formula for in-hospital mortality was 0.670 (95% confidence interval: 0.574–0.767). CONCLUSIONS: This study showed that our predictive formula, consisting of factors available immediately after ambulance transport in older patients, is feasible with sufficient discrimination ability and reliability.