Distributions of local oxygen saturation and its response to changes of mean arterial blood pressure in the cerebral cortex adjacent to arteriovenousmalformations

Background and Purpose-To test the hypothesis that neither "steal" as corti cal ischemia caused by reduced perfusion pressure nor "breakthrough" on the grounds of loss of pressure autoregulation exist in brain tissue surroundi ng arteriovenous malformations (AVMs), we established patterns of cortical oxygen saturation (So,) adjacent to AVMs and its behavior after alterations of mean arterial blood pressure. Methods-With a microspectrophotometer, So, was scanned in the cortex around AVMs of 44 patients before and after resection and in that of a non-AVM gr oup (n =42) before transsylvian dissection. Autoregulation was evaluated by linear regression analysis after elevation of mean arterial blood pressure (5 mu g/min IV noradrenaline). So, values were calculated as medians, perc entage of critical values (<25% SO2), and coefficients of variance (approxi mate heterogeneity of So, distributions). All values are given as mean+/-SD . Results-Forty patients with AVM had an uneventful postoperative course (gro up A). Four hyperemic complications ("breakthrough") occurred (group B). Au toregulation was tested intact in all groups at all times. Preoperative So, distributions in groups A and C (non-AVMs) were identical. In group B, sig nificantly (P<0.05) lower medians (group A, 52.9+/-16.3%; group B, 44.2+/-1 7.1%; group C, 51.9+/-11.5% SO2), more critical values (group A, 6.5+/-5.1% ; group B, 14.7+/-11.1%; group C, 7.1-+-4.9%), and heterogeneous So, distri butions (group A, 20.2+/-12.7%; group B, 27.9+/-12.4%; group C, 26.8+/-10.9 %) were seen. Increase of median values was significantly higher in group B (76.3+/-10.4% SO2) than in group A (65.9+/-13.4% SO2) after resection. Conclusions-Severely hypoxic areas are uncommon in the cortex adjacent to A VMs and occur predominantly in patients prone to hyperemic complications. R educed perfusion pressure is compensated in most cases, and moderate hypere mia prevails after excision. Reperfusion into unprotected capillaries of se verely hypoxic cortical areas results in "breakthrough," for which vasopara lysis appears not to be the underlying mechanism.