Low-flow cardiopulmonary bypass: Importance of blood pressure in maintaining cerebral blood flow

Abstract

Background During cardiopulmonary bypass (CPB), global hypoperfusion of the brain has been shown to result in ischemic insult and subsequent neurologic injury. Methods We measured cerebral blood flow during independent 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 °C. Pump flow rate and arterial blood pressure were altered in varied sequence to each of four conditions: (1) full flow (2.23 ± 0.06 L · min−1 · m−2, mean ± 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 flow (0.75 L · min−1 · m−2) at low pressure (23 ±3 mm Hg). During each of these hemodynamic conditions cerebral blood flow was measured by washout of intracarotid xenon 133. Results Cerebral blood flow was greater at high 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 (27.6 ± 9.9 versus 16.8 ± 3.7 mL · min−1 · 100 g−1) (p < 0.01). At comparable mean arterial blood pressure, alteration of pump flow rate produced no significant change in cerebral blood flow. Conclusions These results indicate that during low-flow CPB, mean arterial pressure should be maintained within the brain's autoregulatory range to maximize cerebral blood flow. During cardiopulmonary bypass (CPB), global hypoperfusion of the brain has been shown to result in ischemic insult and subsequent neurologic injury. We measured cerebral blood flow during independent 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 °C. Pump flow rate and arterial blood pressure were altered in varied sequence to each of four conditions: (1) full flow (2.23 ± 0.06 L · min−1 · m−2, mean ± 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 flow (0.75 L · min−1 · m−2) at low pressure (23 ±3 mm Hg). During each of these hemodynamic conditions cerebral blood flow was measured by washout of intracarotid xenon 133. Cerebral blood flow was greater at high 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 (27.6 ± 9.9 versus 16.8 ± 3.7 mL · min−1 · 100 g−1) (p < 0.01). At comparable mean arterial blood pressure, alteration of pump flow rate produced no significant change in cerebral blood flow. These results indicate that during low-flow CPB, mean arterial pressure should be maintained within the brain's autoregulatory range to maximize cerebral blood flow.