Anaesthetics, inhalational halogenated

The correlation between anaesthetic potency and lipid solubility shown in Fig. 2.10 is valid for most inhaled anaesthetics and the product MAC X oil/gas partition coefficient (which should of course be a constant) varies by only a factor of 2 or 3 for potencies ranging over 100 000-fold. This constancy implies that inhaled anaesthetics act in the same manner at a specific hydrophobic site (the so-called unitary theory of anaesthesia). This has been challenged by more recent work that has identified compounds, including alkanes and poly-halogenated and perfluorinated compounds, which do not obey the Meyer- Overton hypothesis. It has been suggested that a contributory cause of deviation from this hypothesis may be the choice of lipid to represent the anaesthetic site of action of these compounds, implying that there may be multiple sites of action for inhaled anaesthetics. 

Gases of interest are nitrous oxide and the inhalation vapours (or volatile halogenated anaesthetics) such as halothane (CF3CHBrCl), isoflurane (CHF2OCHCICF3) and enflurane (CHCIFCF2OCHF2). In this section electrochemical studies on nitrous oxide, halothane and isoflurane will be discussed. 

Halogenated inhalational anaesthetics Miscellaneous inhalational anaesthetics Barbiturate parenteral anaesthetics Miscellaneous parenteral anaesthetics... 

The early members of the homologous series of ethers are low boiling, flammable liquids. Diethylether was an early anaesthetic but it is little used now, having been replaced with non-flammable inhalation anaesthetics such as enflurane, which is a halogenated ether (Fig. 5.21). Such anaesthetics act via a non-spedlic mechanism where they dissolve in lipid membranes and, in the case of anaesthesia, they dissolve in neurological membranes, thus preventing them from functioning properly. 

The presence of ethers in the atmosphere is almost entirely the result of direct emissions from anthropogenic sources (e.g., Arif et al., 1997 Intergovernmental Panel on Climate Change, 2001 Johnson and Andino, 2001 http //en.wikipedia.org/wiki/Ethers and references therein). These sources can be quite varied and species dependent for example, many ethers are commonly used as industrial solvents many are formed as combustion intermediates and in the burning of biomass various branched ethers (e.g., methyl tert-butyl ether) are (or have been) used as fuel additives to increase octane number and reduce CO emissions dimethyl ether has being proposed as an alternative diesel fuel many fluorinated species have been manufactured, evaluated and used as possible chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) replacement compounds some halogenated species are used as inhalation anaesthetics or as chlorofluorocarbon replacements and polybrominated diphenyl ethers (PBDEs) are used as flame retardants. There are no major routes to ether formation in the atmosphere itself. 

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