Protective effects of volatile agents against methacholine-induced bronchoconstriction in rats

Background: The protective properties of common volatile agents against gen eralized lung constriction have previously been addressed only via estimati ons of parameters that combine airway and tissue mechanics. Their effective ness in preventing airway constriction have not been compared systematicall y. Therefore, the authors investigated the abilities of halothane, isoflura ne, sevoflurane, and desflurane to provide protection against airway constr iction induced by methacholine. Methods: Low-frequency pulmonary impedance data were collected in open-ches t rats under baseline conditions and during three consecutive intravenous i nfusions of methacholine (32 mug.kg(-1).min(-1)) while the animals were ane sthetized with intravenous pentobarbital (control group). Methacholine chal lenges were performed in four other groups of rats, first during intravenou s anesthesia and then repeated during the inhalation of halothane, isoflura ne, sevoflurane, or desflurane at concentrations of 1 and 2 minimum alveola r concentration (MAC). Airway resistance and inertance, parenchymal damping , and elastance were estimated from the impedance data by model fitting. Results: The methacholine-induced increases in airway resistance during int ravenous pentobarbital anesthesia (204 +/- 53%) were markedly and significa ntly (P < 0.005) reduced by 1-MAC doses of halothane (80 +/- 48%), isoflura ne (112 +/- 59%), sevoflurane (68 +/- 34%), and desflurane (96 +/- 34%), wi th no significant difference between the gases applied. Increasing the conc entration to 2 MAC did not lead to any significant further protection again st the increase in airway resistance, Conclusions: These data demonstrate that isoflurane, sevoflurane, and desfl urane are as effective as the widely accepted halothane in protecting again st methacholine-induced air-way constriction.