A COMPARISON OF THE CEREBRAL PRESSURE-FLOW RELATIONSHIP FOR HALOTHANE AND ISOFLURANE AT HEMODYNAMICALLY EQUIVALENT END-TIDAL CONCENTRATIONS IN THE RABBIT

The cerebral pressure-flow relationship for halolhane and isoflurane was studied at endtidal concentrations which resulted in similar baseline mean arterial pressure (MAP). Two groups of New Zealand white rabbits (n = 8; each group) were studied with five regional blood flow determinations in each animal. Blood flow was determined by injecting radioactive microspheres during the following conditions: injection 1: after stable 2.05 per cent endtidal isoflurane (1.OMAC) Group I; or after stable 0.74 ± 0.04 per cent endtidal halothane (0.53 MAC) Group H. Injections 2-5: after MAP was increased 20, 40, 60, and 80 per cent respectively above baseline MAP by phenylephrine infusion. Baseline MAP was the same for both groups(64.3 ± 3.1 vs 67.2 ± 2.0 mmHg; mean ± SEM; Group I and H respectively). Baseline total CBF(tCBF; 0.68 ± 0.03vs 0.86 ± 0.05)andhemisphericCBF(hCBF;0.64 ± 0.03 vs 0.96 ± 0.06) were significantly greater in Group H; no significant difference between groups was seen for baseline posterior fossa CBF(pCBF;0.79± 0.06vs0.75 ± 0.04). For each experiment a pressure-flow curve was generated by curvilinear regression analysis. Significantly greater phenylephrine concentrations were required for injections 2-5 in Group H. Mean slopes and intercepts were derived for each group. Within each group comparison of the pressure-flow curves for hCBF vs MAP and pCBF vs MAP showed autoregulation was less impaired in posterior fossa structures (cerebellum and brain stem) for both anaesthetic agents (P ± 0.05). For all regions examined, the slope of the pressure-flow curve was significantly less steep during 1.0 MAC isoflurane anaesthesia, indicating cerebrovascular autoregulation was less impaired with isoflurane. © 1990 Canadian Anesthesiologists.