CEREBROVASCULAR RESPONSE TO CARBON-DIOXIDE DURING SODIUM NITROPRUSSIDE-INDUCED AND ISOFLURANE-INDUCED HYPOTENSION

We have examined the cerebrovascular response to carbon dioxide during normotension, sodium nitroprusside (SNP)-induced hypotension and high dose isoflurane-induced hypotension in 10 patients who received a sta ndardized general anaesthetic. Carbon dioxide reactivity was determine d by varying Pa-CO2 between 3.0 and 8.0 kPa and recording simultaneous ly blood flow velocity from the middle cerebral artery (vmca). The pai red vmca-Pa-CO2 data were analysed using linear regression to determin e carbon dioxide reactivity. During hypotension, both high-dose isoflu rane and SNP reduced significantly mean absolute (from 17.4 (SEM 2.3) to 13.0 (1.7) and 8.8 (1.3) cm s(-1) kPa(-1), respectively; P < 0.05) and relative (from 32.5 (3.8) to 23.6 (2.0) and 15.5 (1.3)% kPa(-1), r espectively; P < 0.05) cerebrovascular reactivity to carbon dioxide. T his reduction was greater during SNP-induced hypotension (P < 0.05). W e conclude that cerebrovascular reactivity to carbon dioxide was atten uated during isoflurane and SNP-induced hypotension, and that it was b etter preserved during isoflurane-induced hypotension.