Cerebral autoregulation during deep hypothermic nonpulsatile cardiopulmonary bypass with selective cerebral perfusion...

We evaluated effects of hypothermic cardiopulmonary bypass on the cerebral circulation and metabolism of six dogs over a temperature range of 37 degrees to 20 degrees C under alphastat acid-base regulation (uncorrected for body temperature). Cerebral metabolic rate for oxygen was determined from the difference between arterial and sagittal sinus blood oxygen contents, and direct cerebral blood flow measurements of the venous outflow from the isolated sagittal sinus. After core cooling at a constant perfusion flow rate of 80 ml/kg/min, cerebral blood flow significantly reduced to 10.0 +/- 1.1 ml/100 gm/min at 20 degrees C (20% +/- 2% of that at 37 degrees C) because of an increase in the cerebral vascular resistance (339% +/- 48%). Cerebral metabolic rate for oxygen reduced to 18% +/- 2%. The upper body vascular resistance decreased to a greater extent than the lower body resistance (37% +/- 4% versus 82% +/- 12%). In the selective cerebral perfusion system at 20 degrees C, when perfusion pressure (mean carotid arterial pressure minus central venous pressure) was lowered from 90 mm Hg by graded reduction of the perfusion flow rate, cerebral blood flow remained constant down to a perfusion pressure of 40 mm Hg, then steeply declined. Cerebral metabolic rate for oxygen also kept a constant level down to 30 mm Hg, then fell abruptly. Definite autoregulatory response was detected even in profound hypothermic nonpulsatile cardiopulmonary bypass. These results suggest that cerebral perfusion flow should be regulated so as to keep the perfusion pressure within the range of cerebral autoregulation to prevent cerebral ischemia or hyperperfusion, especially during selective cerebral perfusion for operations on the aortic arch.