The effect of change in mean arterial pressure on arterio-jugular bulb venous oxygen content difference under hypothermic cardiopulmonary bypass

Abstract

Introduction: Decreased cerebral blood flow (CBF) secondary to hypotension during cardiopulmonary bypass (CPB) has been claimed to cause central nervous system (CNS) dysfunction. [1] However, some studies have claimed that CBF autoregulation is maintained above a MAP of 55 mm Hg. [2] Change in cerebral arterio-jugular bulb oxygen content difference (AJDO2), calculated from change in jugular venous bulb oxygen saturation can reflect alteration in CBF if the hemoglobin concentration and core temperture are kept constant. [2] This study was designed to test the hypothesis that changes in MAP (dMAP) during CPB will be accompanied by changes in the AJDO2 (dAJDO2) in the opposite direction. Methods: 21 adults undergoing open heart surgery under hypothermic CPB at 28[degree sign]C and alpha-stat blood gas management, with pump flows of 21 min (-1) m-2 were studied. MAP was maintained at two levels in each patient for 10 to 15 minutes: a low of [approximate] 50 mm Hg and a high of [approximate]90 mm Hg using sodium nitroprusside or phenylephrine infusions. Arterial and jugular venous bulb blood samples were drawn at each level and AJDO2 values were calculated. Pearson's correlation analysis was done between dMAP and dAJDO2. Paired t-test were done between the AJDO2 values at successive MAP setting. Results: There were 46 transitions of MAP in the 21 patients. There was no significant correlation between dMAP and dAJDO2. The paired t-test showed no significant difference in the AJDO2 between successive MAP transitions. (p>0.05). Table 1Table 1Discussion: This study shows that there is no consistent relationship between the AJDO2 and MAP during non-pulsatile moderately hypothermic CPB in a MAP range of 50-90 mm Hg. This may imply that CBF autoregulation is maintained under these conditions.