Use of APACHE II Classification to Evaluate Outcome and Response to Therapy in Acute Renal Failure Patients in a Surgical Intensive Care Unit

Abstract

The study objective was to determine the applicability of the acute physiology and chronic health evaluation (APACHE) II score in surgical patients with acute renal failure (ARF) requiring dialytic support, and to assess its utility in evaluating data from this specific disease group. This was a retrospective, partly prospective follow-up study of patients who developed ARF during their course of stay on the surgical intensive care unit (ICU) of a Dutch university hospital from January 1, 1986, to January 31, 1994. A total of 111 patients were identified, of whom 104 patients were considered eligible for this study. Data for the individual APACHE II scores were calculated from the most deranged values during the initial 24 h of ICU admission (APACHE II₁) and on the day dialytic support was instituted (APACHE II₂). The ratio between the two APACHE II scores was also calculated for each patient (AP₂/AP₁ ratio). Receiver operating characteristic curves (ROC) were constructed. Other variables evaluated included age, sex, serum creatinine, diagnostic category, time from ICU admission to start of dialytic support, and the type of dialytic support. Of these 104 patients (median age 64; range 23–85 years), 51 (50%) survived to leave the ICU, of whom 47 (46%) survived to leave hospital. The APACHE II₂ score (27.0±4.4 vs. 22.4 ± 3.5; p < 0.001) and AP₂/AP₁ ratio (1.12 ± 0.09 vs. 0.97 ± 0.06; p < 0.001) were significantly higher for nonsurvivors as compared to survivors. The ROC curve was most discriminative for the AP₂/AP₁ ratio (area under the curve 0.92) and to a lesser extent for the APACHE II₂ score (area under the curve 0.78). Estimated risk of death with the APACHE II equation did not improve predictive power. Multivariate analysis of various variables revealed the AP₂/AP₁ ratio as the single most important factor predicting death (odds ratio 13.8, p < 0.001). Adjusting for the AP₂/AP₁ ratio, no impact on outcome was observed for age, diagnostic category, time from ICU admission to start of dialytic support, and the type of dialytic support. Above a value of 1.0 of the AP₂/AP₁ ratio, logistic regression revealed a sharp increase in death probability with increasing AP₂/AP₁ ratio. APACHE II, when used at the time of initiation of dialytic support, proved to be a valid way in our surgical ICU to stratify ARF patients by the severity of their illness. Moreover, use of the AP₂/AP₁ ratio further improved the usefulness of this severity index and may help to identify patients who have little chance of survival. Predicting death with the APACHE II equation did not improve predictive power.