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

Vlasta Bari1, Emanuele Vaini1, Angela Fantinato1, Beatrice De Maria2, Beatrice Cairo3, Valeria Pistuddi1, Marco Ranucci1, Alberto Porta3
1Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, 2IRCCS Istituti Clinici Scientifici Maugeri, Milan, 3Department of Biomedical Sciences for Health, University of Milan


Introduction: Cerebral autoregulation (CA) maintains mean cerebral blood flow velocity (MCBFV) stable in spite of variations in mean arterial pressure (MAP). Propofol general anesthesia is known to preserve CA, However, information on the effect of propofol general anesthesia on MCBFV and MAP variability coupling strength at sedation levels typical of major cardiac surgery is limited. Methods: MAP and MCBFV beat-to-beat 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) through a parametric cross-spectral approach. Time domain and spectral markers in the three frequency band were assessed as well. The null hypothesis of coupling was tested by assessing K2 via a surrogate analysis, associating MAP and MCBFV series derived from different patients in the same experimental condition. Results: Time domain markers identified the expected autonomic depression induced by propofol anesthesia. K2 between MAP and MCBFV original series was significantly higher than that assessed between surrogate pairs during PRE and it was reduced in the three frequency bands during POST to a level comparable to the one of surrogates. Conclusions: Propofol general anesthesia induces a decoupling of MCBFV and MAP that favors situations of stable MCBFV in response to slow modifications of MAP. Anyway, a full decoupling during propofol anesthesia might hide the limited resources of the cerebrovascular control to actively regulate MCBFV.