Regional perfusion abnormalities with phenylephrine during normothermic bypass

Background. Hypotension and vasopressors during cardiopulmonary bypass may contribute to splanchnic ischemia. The effect of restoring aortic pressure on visceral organ, brain, and femoral muscle perfusion during cardiopulmonary bypass by increasing pump flow or infusing phenylephrine was examined. Methods. Twelve anesthetized swine were stabilized on normothermic cardiopulmonary bypass. After baseline measurements, including regional blood flow (radioactive microspheres), aortic pressure was reduced to 40 mm Hg by decreasing the pump flow. Next, aortic pressure was restored to 65 mm Hg either by increasing the pump flow or by titrating phenylephrine. The animals had both interventions in random order. Results. At 40 mm Hg aortic pressure, perfusion to all visceral organs and femoral muscle, but not to the brain, was significantly reduced. Increasing pump flow improved perfusion to the pancreas, colon, and kidneys. In contrast, infusing phenylephrine (2.4 ± 0.6 μg·kg^-1·min^-1) increased aortic pressure but failed to improve splanchnic perfusion, so that significant perfusion differences existed between the pump flow and phenylephrine intervals. Conclusions. Increasing systemic pressure during cardiopulmonary bypass with phenylephrine causes significantly lower values of splanchnic blood flow than does increasing the pump flow. Administering vasoconstrictors during normothermic cardiopulmonary bypass may mask substantial hypoperfusion of splanchnic organs despite restoration of perfusion pressure.