Effects of Bypas's on CO₂ Cerebrovascular Reactivity in Ischaemic Cerebrovascular Diseases – Based on the Intra-Operative LCBF and CO₂ Cerebrovascular Reactivity Studies

Summary

 The authors evaluated the effects of superficial temporal to middle cerebral artery (STA-MCA) bypass on CO₂ cerebrovascular reactivity (CVR) in ischaemic 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. Single photon emission computed tomography (SPECT) with acetazolamide (ACZ) activation 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 resolved their steal phenomenon. 2) Before bypass, the mean LCBF was significantly (p<0.05) lower than the control level. After bypass, the mean LCBF significantly (p<0.05) increased. 3) In the postoperative SPECT findings, 13 cases showed a disturbed response to ACZ. The CO₂ CVR value in these 13 cases was −1.21±1.19%/mmHg, which was significantly (p<0.05) low compared to the values for the 6 cases showing normal postoperative ACZ responses.

 In ischaemic CVDs before bypass, the CO₂ CVR values were extremely low. After bypass, however, CO₂ CVR and LCBF values significantly improved. SPECT findings, including ACZ challenge, correlated well to the LCBF and CO₂ CVR values. 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-operative response to CO₂.