[Transcranial Doppler sonography during pulsatile and non-pulsatile extracorporeal circulation]

Transcranial Doppler sonography (TCD) was used to determine the mean blood flow velocity of the middle cerebral artery (Vm-MCA) and pulsatility (systolic/diastolic flow velocity = S/D) in 25 patients undergoing aortocoronary bypass grafting before, during, and after extracorporeal circulation (ECC). Preoperatively, none of the patients had signs or symptoms of cerebrovascular disease. ECC was performed with 2.4 l/min per m2 under mild hypothermia (34 degrees C) using membrane oxygenators. After 20 min of nonpulsatile perfusion, ECC was switched to the pulsatile mode for 20 min. Nonpulsatile perfusion was applied for the remaining ECC period. Vm-MCA, S/D, mean arterial blood pressure (MABP), and nasopharyngeal temperature (T.np) were recorded continuously throughout the operation. Hematocrit and paCO2 were determined before, during, and after ECC. Following hemodilution after the introduction of ECC, Vm-MCA was significantly increased compared with the baseline values before ECC. With hematocrit and paCO2 varying insignificantly during ECC, the onset of pulsatile ECC decreased Vm-MCA and MABP simultaneously. After the re-establishment of nonpulsatile ECC, both Vm-MCA and MABP increased again. However, a linear relationship between the two variables could not be documented statistically. During pulsatile ECC, pulsatility (S/D) of the obtained TCD wave forms did not reach baseline values. In 4 cases, TCD showed cessation of diastolic blood flow velocity after induction of ECC or onset of pulsatile ECC. An increase in MABP or changes in ECC regimen promptly restored diastolic TCD signals in these cases. Our results support the concept of increased cerebral blood flow under mild hypothermic ECC. Compared with the nonpulsatile perfusion mode, we found Vm-MCA reduced during pulsatile ECC.(ABSTRACT TRUNCATED AT 250 WORDS)