RELATIVE CHANGES IN CEREBRAL BLOOD-FLOW DURING CARDIAC OPERATIONS USING XE-133 CLEARANCE VERSUS TRANSCRANIAL DOPPLER SONOGRAPHY

Background. Changes in cerebral blood flow (CBF) during cardiac operat ions have implications in terms of postoperative neurologic and neurop sychological dysfunction. Current techniques of CBF measurement are cu mbersome and invasive. Transcranial Doppler sonography offers a noninv asive means of assessing changes in CBF. The aim of this study was val idation of this technique with existing methods of CBF measurement dur ing cardiac operations. Methods. We compared the changes in CBF using xenon-133 clearance with changes in middle cerebral artery velocity by transcranial Doppler sonography (V-MCA) using pH-stat and alpha-stat acid-base management during cardiopulmonary bypass. Measurements were taken (1) before bypass, (2) at 28 degrees C on bypass, (3) at 37 degr ees C on bypass, and (4) after bypass. Relative changes in CBF and V-M CA, calculated as the percent change from the prebypass baseline value normalized to 100%, were used in this analysis. Results. During the h ypothermic phase of cardiopulmonary bypass, CBF and V-MCA increased by 45.9% and 51.8%, respectively (p < 0.001), during pH-stat acid-base m anagement but decreased by only 26.4% and 22.4%, respectively (p < 0.0 001), during alpha-stat acid-base management. Linear regression analys is of the absolute changes in CBF (mL . 100 g(-1) . min(-1)) and V-MCA (cm/s) showed a significant correlation (r = 0.60; r(2) = 0.36; p < 0 .0001), but a better correlation was obtained when relative changes in CBF and V-MCA were compared (r = 0.89; r(2) = 0.79; p < 0.0001). Conc lusions. Measurements of V-MCA, expressed as relative changes of a pre -cardiopulmonary bypass level (using the noninvasive transcranial Dopp ler sonographic technique), can be used to examine CBF changes during cardiopulmonary bypass. (C) 1997 by The Society of Thoracic Surgeons