Effect of PaCO2 on cerebral blood flow distribution during halothane compared with isoflurane anaesthesia in the rat

In order to examine anaesthetic effects on the distribution of cerebral blood flow (CBF) during normo- and hypocapnia, male adult Sprague-Dawley rats were allocated randomly to four groups in a 2 x 2 factorial design, using PaCO2 value and anaesthetic agent as between-group factors. Animals were anesthetized with either 1.38% isoflurane (inspired) or 1.05% halothane (inspired) and the lungs ventilated mechanically at either normocapnia (PaCO2 5.1-5.6 kPa) or hypocapnia (PaCO2 3.1-3.3 kPa) for 1 h. CBF was measured using 14C-iodoantipyrine autoradiography. Local CBF in selected cortical and subcortical regions of interest and area-weighted mean global CBF were calculated. Data were compared by analysis of variance. Normocapnic (mean (SE] CBF for halothane (n = 6) and isoflurane (n = 7) was 120 (8) ml/100 g min-1 (PaCO2 5.6 (0.49) kPa) and 117 (9) ml/100 g min-1 (PaCO2 5.4 (0.5) kPa), respectively. Hypocapnic CBF for halothane (n = 6) and isoflurane (n = 6) was 82 (7) ml/100 g min-1 (PaCO2 3.3 (0.12) kPa) and 82 (6) ml/100 g min-1 (PaCO2 3.2 (0.12) kPa), respectively. Hypocapnia reduced global CBF for both groups by 30% (P less than 0.001), but there was no difference between anaesthetic agents (P greater than 0.8). Hypocapnia decreased CBF in all local structures examined. Although subcortical structures had similar CBF at both normocapnia and hypocapnia, CBF in three cortical samples was greater (P less than 0.05) in both the normocapnic and hypocapnic halothane groups than the corresponding isoflurane groups. The CBF reactivity to changes in PaCO2 was similar for both agents (approximately 2 ml/100 g min-1 mm Hg). (ABSTRACT TRUNCATED AT 250 WORDS)