Changes in cerebral blood flow velocity elicited by surgical stimulation are dependent on the PaCO2 level

Purpose: To investigate the influence of PaCO2 manipulation on the cerebral hemodynamic response to surgical stimulation. Methods: Twenty-one female patients undergoing elective gynecological surge ry performed through a lower median abdominal incision were enrolled. After obtaining steady general anesthesia with 1.7% sevoflurane and 60% nitrous oxide, the patients were randomly assigned to three groups, hypocapnia (PaC O2 = 30 mmHg), normocapnia (PaCO2 = 38 mmHg), and hypercapnia (PaCO2 = 44 m mHg) groups. The changes in mean blood flow velocity in the middle cerebral artery (Vmca) were evaluated using transcranial Doppler ultrasonography du ring nine minutes after surgical incision. Results: The change in Vmca (Delta Vmca) with surgical incision during hype rcapnia (30-36 cm(.)sec(-1)) was significantly greater than during normocap nia (20-22 cm(.)sec(-1)) and hypocapnia (13-15 cm(.)sec(-1)). The Delta Vmc a in the hypocapnia group was significantly smaller than in the normocapnia group. Arterial blood pressure increased with incision but there was no si gnificant difference among the three groups. Conclusion: Cerebral hemodynamic changes evoked by surgical stimulation are attenuated by hypocapnia and are augmented by hypercapnia, even within a c linically relevant range of PaCO2.