Thiopental effect on cerebral blood flow during carotid endarterectomy

To investigate the effect of thiopental on cerebral blood flow (CBF) during carotid endarterectomy, five patients receiving isoflurane-N2O anesthesia were studied. During the period of temporary bypass shunting, a baseline CBF was measured using i.v. Xe washout, and global CBF was calculated from the mean of 10 detectors. Thiopental was given in a dose sufficient (mean 4.5, range 2.6-5.8 mg/kg) to result in burst-suppression on the electroencephalogram (EEG) of approximately 1:1 duration and CBF was measured again. Data were compared using repeated measures analysis of variance. Thiopental significantly reduced mean (+/-SE) CBF (ml/100 g/min) from 37 +/- 6 to 18 +/- 2 (p <0.02). Corresponding PaCO2 (mm Hg) values were 42.8 +/- 1.2 and 41.2 +/- 1.6 and mean systemic blood pressure (mm Hg) was 101 +/- 3 and 100 +/- 6, respectively (NS). Mean % change in CBF was 48 +/- 5 (range 32-62%). There was no relationship between the dose administered and the change in CBF. During steady-state anesthesia, a small dose of thiopental capable of suppressing EEG resulted in a profound reduction in CBF.