Diabetic patients have abnormal cerebral autoregulation during cardiopulmonary bypass

We tested the hypothesis that insulin-dependent diabetic patients with coronary artery bypass graft surgery experience altered coupling of cerebral blood flow and oxygen consumption. In a study of 23 patients (11 diabetics and 12 age-matched controls), cerebral blood flow was measured using ¹³³Xe clearance during nonpulsatile, alpha-stat blood gas managed cardiopulmonary bypass at the conditions of hypothermia and normothermia. In diabetic patients, the cerebral blood flow at 26.6±2.42° C was 25.3±14.34 ml/100 g/min and at 36.9±0.58° C it was 27.3±7.40 ml/100 g/min (p=NS). The control patients increased cerebral blood flow from 20.7±6.78 ml/100 g/min at 28.4±2.81° C to 37.6±8.81 ml/100 g/min at 36.5±0.45° C (p<0.005). The oxygen consumption was calculated from jugular bulb effluent and increased from hypothermie values of 0.52±0.20 ml/100 g/min in diabetics to 1.26±0.28 ml/100 g/min (p=0.001) at normothermia and rose from 0.60±0.27 to 1.49±0.35 ml/100 g/min (p=0.0005) in the controls. Thus, despite temperature-mediated changes in oxygen consumption, diabetic patients did not increase cerebral blood flow as metabolism increased. Arteriovenous oxygen saturation gradients and oxygen extraction across the brain were calculated from arterial and jugular bulb blood samples. The increase in arteriovenous oxygen difference between temperature conditions in diabetic patients and controls was significantly different (p=0.01). These data reveal that diabetic patients lose cerebral autoregulation during cardiopulmonary bypass and compensate for an imbalance in adequate oxygen delivery by increasing oxygen extraction.