Abstract
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.
Résumé
Chez deux groupes de huit lapins blancs de la Nouvelle-Zélande anesthésiés avec soit 2,05 pour cent (1,0 MAC) d’isoflurane ou 0,74 ± 0,04 pour cent (0,53 MAC) d’halothane (mesurés en fin d’expiration) de façon à obtenir une pression arterielle moyenne de depart semblable (64,3 ± 3,1 vs 67,2 ± 2,0 mmHg; moyenne ± erreur-type), nous avons mesuré le débit sanguin cérébral (DSC) par injection de microsphères radioactives. Nous avons ensuite répété cette mesure quatre fois sous perfusion de phényléphrine alors que la pression artérielle s’élevait à 120, 140, 160 et 180 pour cent de sa valeur de base. Au départ, le DSC global était plus faible avec l’isoflurane (0,68 ± 0,03 vs 0,86± 0,05ml· g-1 · min-1) tout comme le DSC hémisphérique (0,64 ± 0,03 vs 0,96 ± 0,06) tandis que le DSC de la fosse postérieure était semblable dans les deux groupes (0,79 ± 0,06 vs 0,75 ± 0,04). On du utiliser plus de phényléphrine pour augmenter la pression sous halothane que sous isoflurane. Pour chaque groupe, nous avons pu établir la pente et l’origine moyennes des courbes pression-débit générées par régression curvilinéaire. Ces courbes nous ont permis de constater que dans les deux groupes, l’autorégulation était moins altérée dans les structures de la fosse postérieure (cervelet et tronc cérébral) que dans celles des hémisphères (P < 0,05). Parailleurs, dans toutes les structures étudiées, et aux doses employées, l’auto-régulation cérébrovasculaire était mieux conservée avec l’isoflurane qu’avec l’halothane.
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Supported by a grant to Dr. Mutch from the Medical Research Council of Canada.
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Mutch, W.A.C., Patel, P.M. & Ruta, T.S. A comparison of the cerebral pressure-flow relationship for halothane and isoflurane at haemodynamically equivalent end-tidal concentrations in the rabbit. Can J Anaesth 37, 223–230 (1990). https://doi.org/10.1007/BF03005474
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DOI: https://doi.org/10.1007/BF03005474