A COMPARISON OF CEREBRAL BLOOD-FLOW REACTIVITY TO CO2 DURING HALOTHANE VERSUS ISOFLURANE ANESTHESIA FOR CAROTID ENDARTERECTOMY

The effects of isoflurane or halothane on cerebral blood flow (CBF) reactivity to changes in arterial carbon dioxide tension (PaCO2) during carotid endarterectomy were compared using the intravenous method of Xe-133-CBF determination. Patients, aged 65 +/- 3 yr (mean +/- SE), received O2 and N2O (1:1) and either 0.75% isoflurane (n = 7) or 0.5% halothane (n = 7). Patient demographic and clinical data were similar for both groups and followed the expected strata of patients with ischemic cerebrovascular disease. Measurements were made during the period of temporary bypass shunting. In the isoflurane group, increasing PaCO2 from 33.3 +/- 1.4 to 43.4 +/- 1.3 mm Hg resulted in a significant (P < 0.05) increase in CBF from 21 +/- 1 to 35 +/- 4 mL.100 g-1.min-1. In the halothane group, increasing PaCO2 from 31.1 +/- 1 to 39.4 +/- 1.6 mm Hg resulted in a significant increase in CBF from 26 +/- 3 to 37 +/- 3 mL.100 g-1.min-1. Mean CBF reactivity to changes in PaCO2 (mL.100 g-1.min-1.mm Hg-1) was 1.74 +/- 0.39 for isoflurane and 1.78 +/- 0.4 for halothane (not significant), corresponding to a relative change of 4.8% +/- 0.8% and 5.2% +/- 1.3% per mm Hg, respectively. There is no significant difference between halothane and isoflurane in their effects on CO2 reactivity in the mildly hypocapnic to normocapnic range.