Intraoperative oliguria predicts acute kidney injury after major abdominal surgery

Background. The threshold of intraoperative urine output below which the risk of acute kidney injury (AKI) increases is unclear. The aim of this retrospective cohort study was to investigate the relationship between intraoperative urine output during major abdominal surgery and the development of postoperative AKI and to identify an optimal threshold for predicting the differential risk of AKI. Methods. Perioperative data were collected retrospectively on 3560 patients undergoing major abdominal surgery (liver, colorectal, gastric, pancreatic, or oesophageal resection) at Kyoto University Hospital. We evaluated the relationship between intraoperative urine output and the development of postoperative AKI as defined by recent guidelines. Logistic regression analysis was performed to adjust for patient and operative variables, and the minimum P-value approach was used to determine the threshold of intraoperative urine output that independently altered the risk of AKI. Results. The overall incidence of AKI in the study population was 6.3%. Using the minimum P-value approach, a threshold of 0.3 ml kg(-1) h(-1) was identified, below which there was an increased risk of AKI (adjusted odds ratio, 2.65; 95% confidence interval, 1.77-3.97; P < 0.001). The addition of oliguria < 0.3 ml kg(-1) h(-1) to a model with conventional risk factors significantly improved risk stratification for AKI (net reclassification improvement, 0.159; 95% confidence interval, 0.049-0.270; P=0.005). Conclusions. Among patients undergoing major abdominal surgery, intraoperative oliguria < 0.3 ml kg(-1) h(-1) was significantly associated with increased risk of postoperative AKI.