Propofol general anesthesia decreases the coupling strength between mean arterial blood pressure and mean cerebral blood flow velocity in patients undergoing coronary artery bypass grafting

Cerebral autoregulation (CA) maintainsmean cerebral blood flow velocity (MCBFV) stable in spite ofvariations in mean arterial pressure (MAP). Propofol anesthesia is known to preserveCA, although informationon the anesthesia effect on MCBFV and MAP variability coupling at sedation levelstypical of major cardiac surgeryislimited. MAP and MCBFVtime serieswere respectively recordedfrom radial artery and left middle cerebral artery via transcranial Doppler,before (PRE) and after (POST) general anesthesia induction with propofol and remifentanil in 10 male subjects (age 64.7±7.0 years) undergoing coronary artery bypass grafting.Squared coherence(K2)wascomputed inthe typical bandsof CA, namely very low (0.02-0.07 Hz), low (0.07-0.15 Hz) and high frequency (0.15-0.4 Hz). The null hypothesis of coupling was tested through a surrogate analysis associatingMAP and MCBFV series taken from different patientsin the same experimental condition. MAP and MCBFV original series were significantly more associated than surrogate ones during PRE. K2was reduced in the three frequency bandsduring POSTto a level comparable with surrogates. By decoupling MCBFVandMAP propofol general anesthesiafavorssituations of stable MCBFV in response to slow modifications of MAPbut the full decoupling might hide the limited resources of the cerebrovascular control toactively regulateMCBFV.