LOW-FLOW CARDIOPULMONARY BYPASS - IMPORTANCE OF BLOOD-PRESSURE IN MAINTAINING CEREBRAL BLOOD-FLOW

Background. During cardiopulmonary bypass (CPB), global hypoperfusion of the brain has been shown to result in ischemic insult and subsequen t neurologic injury. Methods. We measured cerebral blood flow during i ndependent manipulations of arterial blood pressure and pump flow rate to determine which of these hemodynamic parameters regulates cerebral perfusion during CPB. Seven adolescent baboons were placed on CPB and cooled to 28 degrees C. Pump now rate and arterial blood pressure wer e altered in varied sequence to each of four conditions: (1) full flow (2.23 +/- 0.06 L . min(-1). m(-2), mean a standard deviation) at high pressure (61 +/- 2 mm Hg), (2) full flow (2.23 +/- 0.06 L . min(-1). m(-2)) at low pressure (24 +/- 3 mm Hg), (3) low flow (0.75 L . min(-1 ). m(-2)) at high pressure (62 +/- 2 mm Hg), and (4) low now (0.75 L . min(-1). m(-2)) at low pressure (23 +/- 3 mm Hg). During each of thes e hemodynamic conditions cerebral blood now was measured by washout of intracarotid xenon 133. Results. Cerebral blood now was greater at hi gh blood pressure than at low pressure during CPB both at low flow (34 +/- 8.3 versus 14.1 +/- 3.7 mL . min(-1). 100 g(-1)) and full flow (2 7.6 +/- 9.9 versus 16.8 +/- 3.7 mL . min(-1). 100 g(-1)) (p < 0.01). A t comparable mean arterial blood pressure, alteration of pump flow rat e produced no significant change in cerebral blood now. Conclusions. T hese results indicate that during low-flow CPB, mean arterial pressure should be maintained within the brain's autoregulatory range to maxim ize cerebral blood now.