Differences Between Central Venous and Cerebral Tissue Oxygen Saturation in Anaesthetised Patients With Diabetes Mellitus

The brain has high oxygen extraction, thus the regional cerebral tissue oxygen saturation (rSO(2)) is lower than the central venous oxygen saturation (ScvO(2)). We hypothesised that diabetes widens the physiological saturation gap between ScvO(2) and rSO(2) (gSO(2)), and the width of this gap may vary during various phases of cardiac surgery. Cardiac surgery patients with (n = 48) and without (n = 91) type 2 diabetes mellitus (T2DM) underwent either off-pump coronary artery bypass (OPCAB) or other cardiac surgery necessitating cardiopulmonary bypass (CPB) were enrolled. rSO(2) was measured by near-infrared spectroscopy (NIRS) and ScvO(2) was determined simultaneously from central venous blood. rSO(2) was registered before and after anaesthesia induction and at different stages of the surgery. ScvO(2) did not differ between the T2DM and control patients at any stage of surgery, whereas rSO(2) was lower in T2DM patients, compared to the control group before anaesthesia induction (60.4 ± 8.1%[SD] vs. 67.2 ± 7.9%, p<0.05), and this difference was maintained throughout the surgery. After anaesthesia induction, the gSO(2) was higher in diabetic patients undergoing CPB (20.2 ± 10.4% vs. 12.4 ± 8.6%, p < 0.05) and OPCAB grafting surgeries (17.0 ± 7.5% vs. 9.5 ± 7.8%, p < 0.05). While gSO(2) increased at the beginning of CPB in T2DM and control patients, no significant intraoperative changes were observed during the OPCAB surgery. The wide gap between ScvO(2) and rSO(2) and their uncoupled relationship in patients with diabetes indicate that disturbances in the cortical oxygen saturation cannot be predicted from the global clinical parameter, the ScvO(2). Thus, our findings advocate the monitoring value of NIRS in T2DM.