Jugular venous bulb oxygen saturation depends on blood pressure during cardiopulmonary bypass

Background. Central nervous system dysfunction after cardiopulmonary bypass is frequent and can be caused by inadequate cerebral perfusion and oxygenation. Methods. To test the effectiveness of cerebral autoregulation during cardiopulmonary bypass, we induced changes in the cerebral perfusion pressure by administering phenylephrine during moderate (29 degrees C) hypothermia. Using the Fick principle, we calculated relative changes in cerebral blood flow from changes in the jugular venous bulb oxygen saturation. Results. Increasing the cerebral perfusion pressure (from 47 +/- 8.2 to 93 +/- 16 mm Hg) induced increases in the jugular venous bulb oxygen saturation by 4.9% and a calculated increase in the cerebral blood now by 19.9%, strongly suggesting impaired cerebral autoregulation. Conclusions. Because cerebral autoregulation is impaired during cardiopulmonary bypass, phenylephrine is effective in increasing the cerebral blood flow and may contribute to the prevention of postoperative neurologic dysfunction, especially in patients who have a low jugular venous bulb oxygen saturation. (C) 1998 by The Society of Thoracic Surgeons.