Associations of individualized versus conventional blood glucose thresholds with acute kidney injury after cardiac surgery: a retrospective observational study

Introduction An adequate perioperative blood glucose target to optimize outcomes after cardiac surgery has not been established. The aim of this study was to compare individualized versus conventional hyperglycemic thresholds in terms of the risk of acute kidney injury (AKI) after cardiac surgery. Methods This single-center observational study included adult patients who underwent cardiac surgery from January 2012 to November 2021. Two separate blood glucose thresholds were used to define intraoperative hyperglycemia. While the conventional hyperglycemic threshold (CHT) was 180 mg/dl in all patients, the individualized hyperglycemic threshold (IHT) was calculated based on preoperative hemoglobin A1c level in each patient: 28.7 × HbA1c (%) – 31.7 (mg/dl). Various metrics of intraoperative hyperglycemia were calculated using these two thresholds: any hyperglycemic episode, duration of hyperglycemia, and area above the thresholds. To normalize the procedure time varied among patients, the duration of hyperglycemia and area above the blood glucose thresholds were divided by the time between the first and last intraoperative blood glucose measurements. The associations of the metrics defined based on the two thresholds with postoperative AKI were compared using a receiver operating characteristic curve and a multivariable logistic regression analysis. The primary outcome was AKI developed within seven days after surgery, which was defined based on the serum creatinine criteria of the Kidney Disease: Improving Global Outcomes criteria. Results Among 2,427 patients analyzed, 823 (33.9%) patients developed acute kidney injury after cardiac surgery. The c-statistics of IHT-defined metrics (0.58–0.59) were significantly higher than those of the CHT-defined metrics (all c-statistics, 0.54) in the DeLong's test (all P <0.001). Except for the presence of any hyperglycemic episode, the duration of hyperglycemia (adjusted odds ratio [OR], 1.10; 95% confidence interval [CI], 1.03–1.17) and area above the threshold (adjusted OR, 1.003; 95% CI, 1.001–1.005) defined based on the IHT were significantly associated with the risk of postoperative AKI. These two metrics defined using the IHT were still significantly associated with the risk of AKI after normalization to surgical procedure time (normalized duration: adjusted OR, 1.62; 95% CI, 1.11-2.37. normalized area: adjusted OR, 1.02; 95% CI, 1.01-1.03). However, none of the CHT-defined metrics were significantly associated with the risk of AKI. Discussion Individually defined intraoperative hyperglycemia better discriminated the development of AKI after cardiac surgery than universally defined hyperglycemia. Intraoperative hyperglycemia was significantly associated with the risk of postoperative AKI only when defined based on the IHT. Blood glucose target in patients undergoing cardiac surgery may need to be individualized according to preoperative glycemic status.