The most potent cerebral vasodilator is: (AIPG 2012)
a. Carbon dioxide is a powerful modulator of cerebrovascular resistance, and perhaps clinically most accessible one. Any change in arteriolar PaCO2 within the range of 20 to 80 torr has a direct effect on cerebral vessels except in neonates, in whom the response to PaCO2 below 30mmHg may be blunted.
b. The CBF changes 1-2ml/ 100g/min for every 1mmHg change in PaCO2 within physiological ranges. On the other hand, PaO2 does not affect CBF and only a reduction of PaO2 to <50 torrhasa significant effect, by stimulating arteriolar dilation. Thehyperoxia decreases CBF, producing a modest 10-15% decrease at 1 atmosphere.
c. The sodiumnitropruside (SNP) is normally characterized as a central vasodilator but during therapeutic hypotension in men it causes a consistent increase in ICP and either no change or a decrease in CBF.
d. However, if SNP is given without inducing hypotension (partial aortic occlusion), the canine studies showed an increase in both CBF and ICP.
e. The nitroglycerine induced hypotension also has almost similar effects.
f. B-Blockers such as, esmolol, labetalol or metoprololare safer but unpredictable in their effect. However they are good for treating intraoperative hypertension.
Ref.: MILLER ANAESTHESIA