The Effect of Arteriovenous Malformation Resection on Cerebrovascular Reactivity to Carbon Dioxide

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Abstract
To investigate the cerebral hemodynamic changes associated with obliteration of arteriovenous malformations (AVMs), were studied 26 patients undergoing total microsurgical AVM resection during isofluorane and N2/O2 anesthesia. Detectors were placed 5 to 6 cm from the margin of the lesion and in a homologous contralateral position. Cerebral blood flow (CBF) was measured using the intravenous xenon-133 technique before and after AVM resection, during both hypocapnia and normocapnia at each stage. Intraoperative changes in CBF were related to a risk score system based on the patient''s history and preoperative angiograms. Seven otherwise healthy patients undergoing spinal surgery were studied to control for anesthetic effects. Patient demographic and clinical data for the AVM group conformed to the expected strata of a large AVM population. The CBF increased after excision (22 .+-. 1 ml/100 g/min before excision to 30 .+-. 2 ml/100 g/min after excision; mean .+-. SE, n = 25, P < 0.002) without a hemispheric difference. CO2 reactivity increased slightly after excision (4.2 .+-. 0.3% change/mm Hg before excision to 4.7 .+-. 0.3% change/mm Hg after excision; n = 14, P < 0.02). The baseline CBF and CO2 reactivity were not different from the control group. There was a weak correlation between the risk score and the percentage of change in the ipsilateral CBF, with a trend for the patients with the lowest risk to have the lowest CBF changes after resection. There was no relationship between CO2 reactivity and risk grade. None of the patients awoke after anesthesia with unexpected neurological deficits. The highest CBF increases were associated with postoperative brain swelling in one patient and fatal intracerebral hemorrhage in another. Both patients had normal CO2 reactivity before excision. One patient suffered postoperative intracerebral hemorrhage, attributable to technical problems, and had no increase in CBF. We conclude that, with an acute increase in teh arteriovenous pressure gradient (and cerebral perfusion pressure) that results from shunt obliteration, there is an immediate global effect of AVM resection to increase CBF. Cerebrovascular reactivity to CO2 remains intact both before and after excision.