The Duration of Postoperative Acute Kidney Injury Predicts In-Hospital Mortality in Critically III Patients after Non-Cardiac Surgery

BACKGROUND: It is known that severity of acute kidney injury (AKI) can be used to predict in-hospital and long term mortality. Another parameter, the duration of AKI, which might better predict in-hospital mortality, has recently been proposed. This study determines whether the duration of postoperative AKI gives additional prognostic information in critically ill patients, after non-cardiac surgery. METHODS: Surgical patients who were admitted to the intensive care unit were enrolled. AKI cases were defined using KDIGO guidelines and categorized according to the tertiles of AKI duration (1st tertile: less than 2 days; 2nd tertile: 3-5 days; 3rd tertile: ≥ 6 days). The hazard ratios (HRs) for in-hospital mortality, after adjustment of multiple covariates, are compared to those without AKI. The predictability of mortality is accessed by calculating the area under the curve (AUC) for the receiver operating characteristic curve. RESULTS: From a total of 467 postoperative patients, 105 developed AKI (1st tertile: 34 cases, 2nd tertile: 35 cases, 3rd tertile: 36 cases) and 362 had no AKI. The overall in-hospital mortality rate is 28.2%. The in-hospital mortality rates are 22.9% (non-AKI), 32.3% (1st tertile), 57.1% (2nd tertile) and 50% (3rd tertile). The HR’s for in-hospital mortality are 1.647, 1.640 and 1.844, compared to the non-AKI group (P = 0.088, 0.043 and 0.041). Cumulative in-hospital survival rates are significantly different for the non-AKI group and the AKI groups (1st, 2nd and 3rd tertiles) (P ＜ 0.001, by log-rank test). The AUC for AKI duration and stage together (0.797) is higher than that for AKI stage alone, using KDIGO stages alone (0.788)(both P ＜ 0.001). CONCLUSION: In addition to severity, APACHE II scores and advanced age, the duration of postoperative AKI may be a predictor of in-hospital mortality in patients, after non-cardiac surgery.