Objective: To evaluate the relationship between the postoperative Acute Physiology and Chronic Health Evaluation (APACHE) II score and mortality at hospital discharge and at 1 yr in liver transplant recipients.
Population: Adult orthotopic liver transplant (OLTX) recipients (n = 599) admitted to the intensive care unit postoperatively at a university hospital.
Methods: The cohort was split randomly into development and validation sets. Three models were compared for each end point: a) the original APACHE II slope with the original APACHE II postgastrointestinal surgery intercept; b) the original APACHE II slope with an OLTX-specific intercept generated from the development set; and c) an OLTX-specific slope and intercept generated from the development set. Goodness-of-fit and calibration were assessed by the Hosmer-Lemeshow C statistic (where p>.05 suggests good fit) and standardized mortality ratios. Discrimination was assessed by receiver operator characteristic area under the curve analysis.
Measurements and main results: Hospital and 1-yr mortality rates were 9.9% and 15.9%, respectively. The APACHE II score was strongly associated with mortality (chi-square, p<.0001), but when used with the original equation, it significantly overestimated hospital mortality (standardized mortality ratio, 0.73 [confidence interval, 0.58-0.99]). Using the OLTX-specific approaches, goodness-of-fit for both hospital and 1-yr mortality was good (p = .2-.57) but discrimination was only moderate (receiver operator characteristic area under the curve, 0.675-0.723).
Conclusions: APACHE II is a good predictor of short- and long-term mortality after liver transplantation, especially when using OLTX-specific coefficients. Because fit and calibration were better than discrimination, APACHE II will be most useful in the prediction of risk for groups of patients (e.g., in clinical trials or institutional comparisons) rather than for individuals. This study raises the possibility that APACHE II may be useful for long-term mortality prediction in other critically ill populations. The overestimation of mortality using the original equation suggests that orthotopic liver transplantation, by reversing the underlying pathophysiology, may modify risk.