Background
Autoregulation is known to be altered in patients with acute liver failure1, 2. Transcranial Doppler is considered as an appropriate technique to gauge cerebral haemodynamics during hepatic failure and liver transplantation3, 4. We aimed at assessing dynamic autoregulation 5 and non invasive cerebral perfusion pressure estimation (nCPP) 6 during an orthotopic liver transplantation (OLT).
Methods
OLT was performed in 10 patients suffering from chronic liver disease. General anesthesia was performed according to a standardized technique. During the surgery, as a routine clinical procedure, arterial blood pressure (ABP) was invasively measured and cerebral blood flow velocity was assessed using transcranial Doppler (TCD Intraview Rimed™) in the middle cerebral artery. Analog signal was digitized, and stored in a computer using a dedicated in-house software. Off line, the correlation coefficient between ABP and FV, termed mean Mxa, was calculated 5 . Mxa close to +1 denotes that slow fluctuations in ABP produce synchronized slow changes in FV indicating defective autoregulation. In anesthetized patients, Mxa<0.4 indicates a preserved autoregulation 7 . nCPP was also calculated as followed: nCPP=(ABPm*FVd/FVm)+14 6 . During every surgery, we defined three time periods: the dissection phase ie from surgical start till portal vein has been clamped, the anhepatic phase when the portal vein is clamped and at least the reperfusion phase when the portal vein is released until the completion of the surgery. All haemodynamic indices were calculated for each time period and averaged.
Results
ABP was relatively stable during the surgery. nCPP followed passively the changes in ABP. Autoregulation significantly weakens in the course of the surgery, and deteriorates significantly whilst anhepatic (p<0.01) the reperfusion phase (p<0.001). Blood flow velocity increased significantly during reperfusion phase (p<0.05).
Conclusion
We have been able to gauge non invasively cerebral haemodynamics during OLT. Our results indicate an alteration of dynamic autoregulation during the liver transplantation, and autoregulation deteriorates pari passu. During the reperfusion phase, autoregulation is severely deranged, indicating cerebral vasodilation. During liver transplant, nCPP looks maintained within a rather normal range, but further investigations are mandatory to assess the validity of this method during liver dysfunction (See Table 1).