Objective: To evaluate whether isoflurane induced hypotension increases the incidence of cerebral vasospasm in intracranial aneurysm surgery.
Methods: Thirty consecutive patients undergoing intracranial aneurysmal surgery without preexisting cerebral ischemia were prospectively randomized into 2 groups: isoflurane induced hypotension group (group A, n = 15) and isoflurane maintained anesthesia group (group B, n = 15). The patients in the group A were performed isoflurane induced hypotension after dura opening by increasing the inhaled concentration of isoflurane to decrease the mean arterial pressure (MAP) by 30 - 40 percent of that of baseline value. After the aneurysm was clipped, the concentration of inhaled isoflurane was decreased so as to stop blood pressure reduction. The patient in group B was given 1 minimum alveolar concentration (MAC) of isoflurane during the whole procedure. The indicators of blood circulation were measured before blood pressure reduction, 30 minutes after blood pressure reduction, just after the clipping of the aneurysm, and 30 minutes after stopping blood pressure reduction. The S100B protein level in cerebrospinal fluid was observed before the controlled hypotension and 0, 2, and 4 h after the aneurysm was clipped. Assessment of the mean blood flow velocity of parent artery and its main branches was performed by microvascular ultrasonics before and after the aneurysm was clipped. The patients were followed-up for one week after the operation to observe the neurological complication.
Results: The MAP was decreased from 95 mm Hg +/- 12 mm Hg to 59 mm Hg +/- 5 mm Hg 30 minutes after the induced hypotension, and resumed to 75 mm Hg +/- 8 mm Hg 30 minutes after the aneurysm was clipped. Compared with those in the group B, both the total systemic vascular resistance and myocardial contract acceleration were decreased in group A, whereas the cardiac output and heart rate remained stable. (2) 4 hours after the aneurysm was clipped the S100B protein level in CSF was increased significantly in both groups, and that in the group A being significantly higher than that in the group B (t = 2.854, P < 0.01). (3) In the group A, the mean arterial flow velocity of distal parent vessels increased by more than 30 percent in 8 out of the 15 patients and 3 of these 8 patients suffered from neurological deficits postoperatively. However, the mean arterial flow velocity of distal parent vessels in the group B increased by more than 30 percent in only 3 of the 15 patients and 2 of these 3 patients suffered from neurological deficits postoperatively.
Conclusion: Isoflurane controlled hypotension may increase the incidence of cerebral vasospasm. Isoflurane induced hypotension for intracranial aneurysm surgery should be cautioned.