Intraoperative Cerebral Tissue Oxygenation and Postoperative Cognitive Dysfunction After on- and off-Pump Coronary Artery Bypass Surgery

Background: The incidence of postoperative cognitive dysfunction (POCD) after cardiac surgery is up to 65% at hospital discharge.1 For a long time it was assumed that POCD is caused by impaired cerebral tissue oxygenation (cSO2) due to the physiological alterations associated with cardiopulmonary bypass (CPB). A recent study showed that preoperative cSO2 and reactivity to O2-administration predicted POCD after on-pump coronary artery bypass grafting (CABG).2 Other (non-randomized) studies have shown correlations between the severity and duration of brain tissue oxygenation and POCD during on- and off-pump CABG.3,4 Our study aimed to compare the depth as well as duration of cerebral tissue desaturations during on- and off-pump CABG, and relate this to the incidence of POCD.Methods:In this ethical committee approved, clinical trial 60 patients undergoing elective CABG under standardized anesthesia (mean age of 63 [SD 9.4]) were randomized to either the on- or off-pump procedure. Primary endpoint was area under the cSO2 curve < 40% of >600sec.%. cSO2 was measured continuously from preinduction of anesthesia until ICU admission with both Invos and ForeSight cerebral oximeters. After baseline cSO2 measurements (room air) 100% O2 was administered for 5 min to assess O2-reactivity. A validated cognitive testing battery (CogState) comprising 4 tests was used to assess cognitive performance preoperatively and 4 days after surgery. POCD was defined as a decline in performance of >2 SD in ≥2 tests.Results:One procedure was converted from on-pump to off-pump after sternotomy at the discretion of the surgeon, resulting in 29 on-pump and 30 off-pump procedures. Baseline characteristics were similar in both study groups. There was no difference in major complications, nor duration of ICU and hospital admission. The primary endpoint occurred in only 3 patients, of whom 1 patient developed postoperative stroke. Other commonly used cut-off values for cerebral desaturation, e.g. a cSO2 <60% or a 20% decrease from baseline cSO2, showed no difference in AUC (table 1). Postoperative cognitive dysfunction (POCD) occurred in 39% and 45% of on- and off-pump patients respectively (p=0.65). Baseline cSO2 was not predictive of POCD, nor was there any predictive value of O2-reactivity (table 2).Conclusion:This randomized trial showed no difference in the incidence of intraoperative cerebral desaturation and POCD between patients undergoing on-pump and off-pump CABG. Although the incidence of POCD was similar to other published studies, the depth and duration of intraoperative cerebral desaturations was less severe in our study population. This suggests that factors other than CPB and cerebral oxygenation play an important pathophysiological role in the development of POCD. Factors such as inflammatory responses to stress, anesthesia and surgery should be considered.5References:1. Ann Thorac Surg 2008; 85: 872-92. Anesthesiology 2011; 114: 58-693. J Cardiothorac Vasc Anesth 2004; 18: 552-84. J Cardiothorac Vasc Anesth 2011; 25: 95-1045. Anaesthesia 2012; 67: 280-93