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Contents:
Basic pharmacologic overviews of the volatile agents are available at anaesthetist.com. Also the WFSA site has a good general overview. Drs. Nickalls and Mapleson have published a set of graphs showing iso-MAC values for the common anaesthetic agents with and without nitrous for patients of different ages (pdf here). MAC 0.7. Predisposes to arrhythmias with high levels of circulating catecholamines and nodal rhythms in children. Profoundly impairs autoregulation of cerebral blood flow. Can initiate malignant hyperthermia.
Mac 1.68. Less soluble than halothane (more rapid onset and offset), fewer arrhythmias and much less chance of MH. Impairs cerebral blood flow autoregulation but to a lesser extent than halothane, can infrequently trigger seizure activity, is metabolised to fluoride in levels that infrequently are significant. Product information from NZ Govt Medsafe, also Wikipedia, FRCA Mediweb and MetroHealth.
Mac 1.14. Similar to enflurane but less soluble (more rapid again) and much less metabolism, can be used in closed circuit. Less effect on cerebral blood flow autoregulation than Enflurane of Halothane. More irritant than Sevoflurane Compared to isoflurane, is less irritant and has more rapid onset and offset, but is metabolised to a greater extent. Mac approx. 2.6 for adults. Excellent for mask induction. Sevoflurane would be ideal for long cases except that it is more expensive than isoflurane and that concerns exist about potential dose and time dependent nephrotoxicity, so that low flows cannot be used for extended periods. Sevoflurane is metabolised to fluoride ion in a dose*time dependent fashion. Additionally, potentially nephrotoxic by-products (compound A etc.) are formed when exposed to warm moist soda lime. Rate of production is increased with baralyme, low flows, high CO2's and long MAC*hr exposures. Fluoride and compound A etc. are not produced to any significant extent if Amsorb is used instead of ordinary soda lime. Current US recommendations are to not use flows less than 1 litre/minute, and to not exceed 2 MAC*hours exposures at flows less than 2 litres/minute with standard soda lime.
The most insoluble volatile agent with fastest onset and offset, causes sympathetic activation with rapid increases in inhaled levels, irritates airways, requires special electronic vapouriser.
Malignant Hyperthermia and volatile anesthetics
CNS effects
Apparatus
Miscellaneous
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