Effect of nimodipine on cerebrovascular response to CO2 in asymptomatic individuals and patients with subarachnoid hemorrhage: a transcranial Doppler ultrasound study.

The cerebrovascular response to CO2 was evaluated by measuring relative changes in blood flow velocity within the middle cerebral artery by transcranial Doppler ultrasonography during normo-, hypo-, and hypercapnia. In seven patients without subarachnoid hemorrhage (five with unruptured arteriovenous malformations and two with aneurysms), the CO2 vasoreactivity was tested on the side of the middle cerebral artery with normal flow velocities opposite the lesion. A baseline CO2 reactivity test was obtained in each patient and then repeated under constant intravenous infusion of nimodipine, 2 mg/hr. Nine patients with ruptured aneurysms who were rated at Hunt and Hess Grades 1 or 2 were operated on within 1 to 3 days after the hemorrhage and treated with nimodipine, 2 mg/hr, given intravenously. In these patients, CO2 vasoreactivity was tested during the second week after the hemorrhage, when the middle cerebral artery velocity was increased by at least 50% of the initial value or more. Nimodipine was then discontinued and, 48 hours later, when the middle cerebral artery velocity was still in the same range, CO2 vasoreactivity was tested again. Two months later, after full recovery from the subarachnoid hemorrhage and normalization of the velocities, a third measurement of CO2 reactivity was obtained as a baseline control. No significant effect of nimodipine on CO2 vasoreactivity could be demonstrated in any of the test periods. In the second week after a subarachnoid hemorrhage, a significant reduction of the cerebrovascular response to CO2 was found (P less than 0.005).