Anaesthetic concentrations of enflurane and methoxyflurane in rat brain in-vivo and in-vitro
Bazil, C.W.; Minneman, K.P.
Journal of Pharmacy and Pharmacology 41(12): 835-839
1989
ISSN/ISBN: 0022-3573 PMID: 2576445 Document Number: 344006
We measured concentrations of enflurance and methoxyflurane in brains of anaesthetized rats and established conditions for reproducing these concentrations in brain tissue in-vitro. Despite a 12-fold difference in inspired potency, brain concentrations resulting in anesthesia were similar for both compounds. However, substantially lower concentrations in the equilibrating gas were necessary to achieve similar tissue concentrations in-vitro, probably because anaesthetic-induced respiratory depression or changes in cardiac output causes incomplete equilibration in-vivo. These studies provide direct evidence that brain concentrations associated with anaesthesia are similar for anaesthetics with different inspired potencies. They also suggest that lower concentrations in the equilibrating gas should be used in-vitro to reproduce clinically relevant tissue concentrations that are necessary to cause anaesthesia in-vivo.