Modifications of cerebral vascular resistance and autoregulation after graft reperfusion during human orthotopic liver transplantation

We have studied cerebral blood flow velocity (CBFV) and cerebral autoregulation (CA) in 23 orthotopic liver transplantation (OLT) patients using transcranial doppler. CBFV was continuously recorded using a fixed (helmet) 2-Mz probe through the trans-temporal window. CA changes were studied using a linear regression analysis of percentile changes in CBFV and mean arterial blood pressure (MABP) after phenylephrine infusion compared with baseline. Pearson's "r" coefficient was considered an index of CA. In case of autoregulation is lost "r" tends to 1, thus representing complete dependence of CBFV on MABP. We regarded the slope coefficient parameter "S" as an index of cerebral vascular resistance (CVR), namely, the ratio of the corresponding variations of CBFV to MABP. Wilcoxon test showed a significant increase in both "r" and "S" between the anhepatic versus postreperfusion phases (within the first hour) and versus recovery in the neohepatic phase (end of surgery). A decreased CVR was observed within the first hour after graft reperfusion producing a loss of CA. These phenomena lead to an increase of CBFV and exposed the brain to hyperperfusion.