Evaluation of Tolerance for Brain Ischemia Following Vasospasm in Patients of Subarachnoid Hemorrhage Using Intraoperative Microvascular Doppler Sonography

Abstract

We evaluated CO₂ reactivity of cortical artery on 25 patients with aneurysmal subarachnoid hemorrhage during craniotomy for clipping of their aneurysms. Every case was operated on within 72 hours from onset of subarachnoid hemorrhage. After clipping of aneurysm, we measured cerebral blood flow velocity and resistance index placed on cortical artery of parasylvian region using microvascular Doppler sonography (DWL Elektronische Systeme GmbH, Multi-Dop X) with the PaCO₂ at 30 mmHg, 40 mmHg and 50 mmHg. We controlled PaCO₂ by alteration of respiratory condition and kept systemic mean arterial blood pressure normotensively during measurement. CO₂ reactivity is regarded as one indication of the capacity to tolerate brain ischemia. We evaluated tolerance for brain ischemia according to the increase ratio of cerebral blood flow velocity and the decrease of resistance index as the PaCO₂ was changed from 30 mmHg to 50 mmHg. We recognized 16 cases as patients who had good CO₂ reactivity according to our criterion. Six other cases reacted to hypercapnia poorly and remaining 3 cases showed abnormal CO₂ response. We investigated the relationship between CO₂ reactivity and the outcome at 1 month after the onset of subarachnoid hemorrhage. These 16 cases whose CO₂ reactivity was good resulted in good outcome (GOS 1:11, GOS 2:5).
Six poor CO₂ reactivity patients had worse outcomes (GOS 1:1, GOS 2:3, GOS 3:2). Unfortunately, the remaining 3 patients whose CO₂ reactivity was abnormal resulted in misery state (GOS 4: 2, GOS 5: 1). On the other hand, 8 patients in our series came down with symptomatic vasospasm during the course. While only 2 of 16 patients who had good CO₂ reactivity suffered from symptomatic vasospasm, half of 6 patients whose CO₂ response was poor and all of 3 patients whose CO₂ reactivity was regarded as abnormal developed symptomatic vasospasm. We can conclude that CO₂ reactivity is closely related to the outcome and the appearance of symptomatic vasospasm. And microvascular Doppler sonography is a very useful and noninvasive method for the intraoperative evaluation of CO₂ reactivity in patients of aneurysmal subarachnoid hemorrhage.