Assessing contemporary intensive care unit outcome:: An updated Mortality Probability Admission Model (MPM0-III)

Objective. To update the Mortality Probability Model at intensive care unit (ICU) admission (MPMo-II) using contemporary data. Design: Retrospective analysis of data from 124,855 patients admitted to 135 ICUs at 98 hospitals participating in Project IMPACT between 2001 and 2004. Independent variables considered were 15 MPMo-II variables, time before ICU admission, and code status. Univariate analysis and multivariate logistic regression were used to identify risk factors associated with hospital mortality. Setting: One hundred thirty-five ICUs at 98 hospitals. Patients. Patients in the Project IMPACT database eligible for MPMo-II scoring. Interventions: None. Measurements and Main Results: Hospital mortality rate in the current data set was 13.8% vs. 20.8% in the MPMo-II cohort. All MPMo-II variables remained associated with mortality. Clinical conditions with high relative risks in MPMo-II also had high relative risks in MPMo-III. Gastrointestinal bleeding is now associated with lower mortality risk. Two factors have been added to MPMo-III: full code resuscitation status at ICU admission, and zero factor (absence of all MPMo-II risk factors except age). Seven two-way interactions between MPMo-II variables and age were included and reflect the declining marginal contribution of acute and chronic medical conditions to mortality risk with increasing age. Lead time before ICU admission and pre-ICU location influenced individual outcomes but did not improve model discrimination or calibration. MPMo-III calibrates well by graphic comparison of actual vs. expected mortality, overall standardized mortality ratio (1.018; 95% confidence interval, 0.996-1.040) and a low Hosmer-Lemeshow goodness-of-fit statistic (11.62; p =.31). The area under the receiver operating characteristic curve was 0.823. Conclusions. MPMo-II risk factors remain relevant in predicting ICU outcome, but the 1993 model significantly overpredicts mortality in contemporary practice. With the advantage of a much larger sample size and the addition of new variables and interaction effects, MPMo-III provides more accurate comparisons of actual vs. expected ICU outcomes.