Transcranial Doppler blood flow velocity versus ¹³³Xe clearance cerebral blood flow during mild hypothermic cardiopulmonary bypass

Objective. Transcranial Doppler (TCD) is used during cardiopulmonary bypass (CPB) to assess cerebral emboli and to estimate cerebral perfusion. We sought to compare TCD middle cerebral artery blood flow velocity (V_mca) to ¹³³Xe clearance cerebral blood flow (CBF) measurements during mild hypothermic CPB thus determining its utility in cerebral perfusion assessment. Methods. Thirty-four patients undergoing mild hypothermic CPB (35 °C) were studied and had comparisons of V_mca and ¹³³Xe CBF at three time intervals, 10, 30 and 60 min after the institution of CPB. Linear regression analysis was performed on data from each of the 3 intervals as well as for pooled data from all 3 periods. Results. The correlation coefficients for the 3 time periods were, r = 0.32 (p = 0.12), r = 0.32 (p = 0.11), r = 0.48 (p = 0.02), respectively. The pooled data correlation had a coefficient of 0.34 (p = 0.003). Conclusion. These findings suggest that TCD V_mca is a relatively poor correlate of CBF during mild hypothermic CPB.