Prospective validation of the intensive care unit admission Mortality Probability Model (MPM0-III)*

OBJECTIVE: To validate performance characteristics of the intensive care unit (ICU) admission mortality probability model, version III (MPM0-III) on Project IMPACT data submitted in 2004 and 2005. This data set was external from the MPM0-III developmental and internal validation data collected between 2001 and 2004. DESIGN: Retrospective analysis of clinical data collected concurrently with care. SETTING: One hundred three (103) adult ICUs in North America that voluntarily collect and submit data to Project IMPACT. SUBJECTS: A total of 55,459 patients who were eligible for MPM scoring (age >or=18; first ICU admission for hospitalization, excludes burns, coronary care, and cardiac surgical patients). INTERVENTIONS: None. MEASUREMENTS: Prevalence of MPM risk factors and their relationship to hospital mortality; calibration and discrimination of MPM0-III model applied to new data. MAIN RESULTS: Seventy-eight ICUs contributed data to both this study and the original development set. Fifty-six ICUs from the original MPM0-III study were replaced by 25 new ICUs in this external validation set. Patient characteristics (type of patient, risk factors, and resuscitation status) were similar to the original 2001-2004 cohort, except for slightly more patients on mechanical ventilation at admission (32% vs. 27%, p < 0.01) and the percentage of patients having no MPM0-III risk factors except age (11% vs. 14%, p < 0.01). Observed deaths were 7331 (13.2%) vs. 7456 predicted, yielding a standardized mortality ratio of 0.983, 95% CI (0.963-1.001). CONCLUSIONS: MPM0-III calibrates on a new population of 55,459 North American patients who include many patients from new ICUs, which helps confirm that the model is robust and was not overfitted to the development sample. Although Project IMPACT participants change over time, 2004-2005 patient risk factors and their relationship to hospital mortality have not significantly changed. The increase in mechanically ventilated patients and reduction in admissions with no risk factors are trends worth following.