Effect of arterial blood pressure on cerebral vein oxygen saturation in the rewarming phase of extracorporeal circulation

Abstract

This study concerns the effects of elevated mean arterial blood pressure (MAP) on decreases in jugular bulb oxygen saturation (SjO2) using fiberoptic jugular bulb oximetry and on cerebral blood flow velocity measured by transcranial Doppler sonography (TCD) during cardiopulmonary bypass (CPB) for coronary artery bypass graft (CABG). 27 ASA III patients undergoing CABG were studied. Anaesthesia was maintained with fentanyl, midazolam and continuous infusion of etomidate. CPB was managed according to alpha-stat conditions under moderate hypothermia (27 degrees C). SjO2 (%) and jugular bulb temperature were measured using a fiberoptic catheter placed in the right jugular bulb via the right internal jugular vein. TCD recordings of middle cerebral artery mean blood flow velocity (Vmean, cm/s) were taken during the investigation period. Data were recorded continuously before and for 40 min following start of rewarming. In group 1 (n = 17) MAP was kept between 55 and 65 mmHg, in group 2 (n = 10) MAP was maintained above 70 mmHg using norepinephrine infusion during rewarming of CPB. Following rewarming MAP was statistically significant elevated in group 2 compared to group 1. In groups 1 and 2, Vmean was increased and SjO2 was decreased to a similar extent during rewarming of CPB. Decreases in SjO2 below 50% were seen in both groups. The present data show decreases in Sjo2 during rewarming regardless to the level of arterial blood pressure (range 55-80 mmHg). This suggests that desaturation during rewarming of CPB is not a function of decreases in MAP since CBF autoregulation appears to be maintained within this pressure range.