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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) maintains mean cerebral blood flow velocity (MCBFV) stable in spite of variations in mean arterial pressure (MAP). Propofol anesthesia is known to preserve CA, although information on the anesthesia effect on MCBFV and MAP variability coupling at sedation levels typical of major cardiac surgery is limited. MAP and MCBFV time series were respectively recorded from 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) was computed in the typical bands of 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 associating MAP and MCBFV series taken from different patients in the same experimental condition. MAP and MCBFV original series were significantly more associated than surrogate ones during PRE. K2 was reduced in the three frequency bands during POST to a level comparable with surrogates. By decoupling MCBFV and MAP propofol general anesthesia favors situations of stable MCBFV in response to slow modifications of MAP but the full decoupling might hide the limited resources of the cerebrovascular control to actively regulate MCBFV.