Impact of Cardiopulmonary Bypass Flow on Cerebral Autoregulation
Condition: Cerebral Autoregulation; Cardiopulmonary Bypass; Mean Arterial Pressure
Study type: Interventional

Summary: 
      Cerebral autoregulation is defined by the capacity of the brain to maintain a constant
      cerebral blood flow (CBF) despite variations of arterial pressure. However, when the arterial
      pressure is below a critical threshold, cerebral blood decreases.

      This critical threshold is called the lower limit of cerebral autoregulation (LLA).

      Cardiopulmonary bypass is a unique environment wherein systemic blood flow is totally
      controlled by the cardiopulmonary bypass pump. High pump flows combined with low arterial
      pressures has been shown to not compromise neurologic postoperative outcomes.

      Our hypothesis is that that LLA may depend on the cardiopulmonary bypass flow, ie the LLA may
      decrease when the cardiopulmonary bypass flow increases, explaining why low arterial pressure
      may be well tolerated.
    

Detailed description: 
      Cerebral tissue perfusion is partly ensured by cardiac output and arterial pressure. In
      cardiac surgery, and especially during bypass surgery, one of the main objectives is to
      maintain sufficient blood flow and an optimal mean arterial pressure (MAP) to limit the
      deleterious consequences of organ hypoperfusion. To have a physiological regional organ blood
      flow, some organs, such as the brain, need a minimum MAP threshold (the lower limit of
      autoregulation, LLA) to ensure a constant cerebral blood flow (CBF). This is known as the
      cerebral autoregulation (CA). As the brain is at high risk of ischemia and definitive
      functional consequences in case of cerebral hypoperfusion, maintaining MAP above the LLA of
      the brain limit the deleterious postoperative neurological outcome.

      CA can be determined by continuously calculating the correlation between MAP and CBF. CBF is
      assessed by continuous monitoring of the middle cerebral artery velocity (mV). moving Pearson
      correlation coefficient between 30 consecutive, paired MAP and cerebral blood flow velocity
      values will be calculated to generate the mean velocity index (Mx). The Blood pressure in the
      autoregulation range is indicated by an Mx value that approaches zero (there is no
      correlation between flow velocity and MAP), whereas an Mx approaching 1 indicates
      dysregulated cerebral blood flow (flow velocity and MAP are correlated). A value of 0.4 is
      accepted as the threshold of CA corresponding to the LLA.

      During cardiopulmonary bypass (CPB), MAP is physiologically related to bypass flow and
      systemic vascular resistance. The adjustment of MAP during CPB is therefore achieved by the
      administration of vasoconstrictors or vasodilators as well as by the variations of the pump
      flow.

      This research assumes that a change in the pump flow rate will lead to a change in the LLA.
      Therefore, if the flow rate is higher, it is possible that the LLA will be lower.

      In this randomized trial, two different rates of pump flow will be compared with respect to
      LLA testing.

      Regional brain oxygen saturation, assessed by near-infrared spectroscopy will also be
      monitored during surgery.
    

Intervention name(s): current versus high pump flow
Intervention type(s): Procedure
Intervention description(s): during each phase of randomized pump flow, arterial pressure will be increased from 40 to 90 mmHg with vasodilators and/or vasoconstrictors
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: parallel affectation
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Diagnostic
Keywords: FlowMapca