Background Cerebral oximetry has been widely used to measure regional oxygen saturation in brain tissue, especially during cardiac surgery. Despite its popularity, there have been inconsistent results on the use of cerebral oximetry during cardiac surgery, and few studies have evaluated cerebral oximetry during off pump coronary artery bypass graft surgery (OPCAB). Methods To evaluate the relationship between intraoperative cerebral oximetry and postoperative delirium in patients who underwent

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... PCAB, we included 1,439 patients who underwent OPCAB between October 2004 and December 2016 and among them, 815 patients with sufficient data on regional cerebral oxygen saturation (rSO2) were enrolled in this study. We retrospectively analysed perioperative variables and the reduction in rSO2 below cut-off values of 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, and 35%. Furthermore, we evaluated the relationship between the reduction in rSO2 and postoperative delirium. Results Delirium occurred in 105 of 815 patients. In both univariable and multivariable analyses, the duration of rSO2 reduction was significantly longer in patients with delirium at cut-offs of <50% and 45% (for every 5 min, adjusted odds ratio(OR) 1.007 [95% Confidence interval (CI) 1.001 to 1.014] and adjusted OR 1.012 [1.003 to 1.021]; p=0.024 and 0.011, respectively). The proportion of patients with an rSO2 reduction <45% was significantly higher among those with delirium (adjusted OR 1.737[1.064 to 2.836], p=0.027). Conclusions In patients undergoing OPCAB, intraoperative rSO2 reduction was associated with postoperative delirium. Duration of rSO2 less than 50% was 40% longer in the patients with postoperative delirium. The cut-off value of intraoperative rSO2 that associated with postoperative delirium was 50% for the total patient population and 55% for the patients younger than 68 years.