THE RELATIONSHIP BETWEEN CEREBRAL BLOOD-FLOW AND TRANSCRANIAL DOPPLERBLOOD-FLOW VELOCITY DURING HYPOTHERMIC CARDIOPULMONARY BYPASS IN ADULTS

A noninvasive, simple, and continuous method to assess cerebral perfus ion during cardiopulmonary bypass (CPB) could help prevent cerebral is chemia. Transcranial Doppler sonography (TCD) allows a noninvasive, on -lice measurement of blood flow velocity in cerebral arteries. The cor relation of TCD-estimated and actual cerebral blood flow (CBF) has not been well studied during CPB. We determined the correlation of middle cerebral artery (MCA) mean velocity and CBF determined by the Kety-Sc hmidt method during nonbypass and two hypothermic bypass flow conditio ns. Sixteen patients undergoing hypothermic (27 degrees C) CPB for cor onary artery bypass grafting and/or valve replacement surgery were enr olled in the study. We were able to determine MCA velocity in only 12 patients. We determined CBF and MCA velocity in each patient during fo ur 15-min study periods: 1) prebypass after sternotomy before aortic c annulation; 2) hypothermic (27 degrees C) CPB with 1.2 L . min(-1). m( -2) pump flow; 3) hypothermic CPB with 2.4 L . min(-1). m(-2) pump flo w, and 4) 30 min after weaning from CPB. There was no difference in th e mean arterial pressure between the two CPB pump blood flows. The poo led change in MCA velocity and CBF as percentage of base-line (prebypa ss) for all patients and at all time points had a correlation of 0.33 (r). A decrease or increase in MCA velocity did not necessarily indica te a corresponding decrease or increase in CBF. This technology maybe of limited usefulness during the circulatory condition of hypothermic, nonpulsatile CPB.