Significance of Induced Hypercapnia Method as Preoperative Study Predicting Results of STA -MCA Bypass Surgery

—In Relation to Induced Hypertension Method (Experimental Study)—

Abstract

Cerebral ischemia was produced by occlusion of the canine middle cerebral artery, and the changes in regional cerebral blood flow (rCBF) and somatosensory evoked potentials (SEP, V₁) were monitored for three hours following production of ischemia, under CO₂ inhalation or with a controlled intravenous infusion of Angiotensin II.
In mild ischemia, in which rCBF was decreased by 20 to 40% compared with the control, rCBF and SEP (V₁) significantly recovered during artificially induced hypercapnia (PaCO₂ 43 to 55 mmHg). However, hypertension caused no or only minimal changes in rCBF and SEP (V₁) in ischemia of this degree.
In moderate ischemia, in which rCBF was decreased by 40 to 60% compared to the control, rCBF and SEP (V₁) were significantly restored by artificially induced hypertension.
Induced hypercapnia and hypertension methods are promising as preoperative tests for predicting the resules of bypass surgery. However, care is needed in assessing the results of these tests since response of cerebral arteries by the two activating methods depends on the degree of ischemia.