Effects of bypass on CO2 cerebrovascular reactivity in ischaemic cerebrovascular diseases - Based on the intra-operative LCBF and CO2 cerebrovascularreactivity studies

The authors evaluated the effects of superficial temporal to middle cerebra l artery (STA-MCA) bypass on CO2 cerebrovascular reactivity (CVR) in ischae mic cerebrovascular diseases (CVDs). Local cerebral blood flow (LCBF) and CO2 CVR in 19 patients with ischaemic CVD subjected to standard STA-MCA bypasses were examined during surgery. Si ngle photon emission computed tomography (SPECT) with acetazolamide (ACZ) a ctivation was also performed before and at 1 month after surgery. The results are as follows. 1) Before bypass, the average CO2 CVR value was -1.50 +/- 2.30%/mmHg (mean +/- SD). SPECT showed disturbed response to ACZ in all cases. Fifteen cases showed the steal phenomenon. After bypass, the mean CO2 CVR value significantly (p < 0.05) increased, and four cases reso lved their steal phenomenon. 2) Before bypass, the mean LCBF was significan tly (p < 0.05) lower than the control level. After bypass, the mean LCBF si gnificantly (p < 0.05) increased. 3) In the postoperative SPECT findings, 1 3 cases showed a disturbed response to ACZ. The CO2 CVR value in these 13 c ases was -1.21 +/- 1.19%/mmHg, which was significantly (p < 0.05) low compa red to the values for the 6 cases showing normal postoperative ACZ response s. In ischaemic CVDs before bypass, the CO2 CVR values were extremely low. Aft er bypass, however, CO2 CVR and LCBF values significantly improved. SPECT f indings, including ACZ challenge, correlated well to the LCBF and CO2 CVR v alues. STA-MCA by pass exerted a favourable effect on the CO2 CVR and LCBF values immediately after bypass in the cases showing a reduced pre-operativ e response to CO2.