Contents:

• Basic pharmacology
  • Halothane
  • Enflurane
  • Isoflurane
  • Sevoflurane
  • Desflurane
• Fluoride and Renal Function
• Malignant Hyperthermia
• CNS effects
• Apparatus
• Miscellaneous

Basic Pharmacology

Basic pharmacologic overviews of the volatile agents are available at anaesthetist.com. Also the WFSA site has a good general overview.

Halothane

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.

• Summary from WSFA, Metrohealth, Wikipedia
• Hepatotoxicity of inhaled agents
• 1996 report of liver damage from NZ

Enflurane

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.

Isoflurane

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

• Product information from NZ Govt Medsafe, also from Wikipedia, MetroHealth

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.

• US FDA information and regulation (see warnings)
• Basic pharmacology from NZ Govt MedSafe Wikipedia and MetroHealth RxList.
• Pub Med abstract of Amsorb in reducing compound A production. PubMed abstract showing in clinical use 1.0 l/min FGF seems OK.
• Brief abstract of Fluoride toxicity

Desflurane

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.

• Basic profiles from MedSafe NZ, MetroHealth Wikipedia Mediweb
• Effect on SEF95, BIS. MF

Fluoride and Renal Function

• Fluoride production with isoflurane vs. sevoflurane - an abstract

Malignant Hyperthermia and volatile anesthetics

• Malignant Hyperthermia by A.Urwyler. (4K)
• Altered sodium current response to intracellular fatty acids in halothane-hypersensitive skeletal muscle. Wieland, Steven J., Qi-Hua Gong, Jeffrey E, (2K)
• basic info from Wikipedia
• Link to other MH info in this textbook

CNS effects

• WFSA notes (start at part 1 if you prefer)
• EEG effects of desflurane - lowers spectral edge like all the others
• The details will be in the full SNACC bibliography on epilepsy and anaesthesia
• Effects of halothane, hypocapnia and hypercapnia on cerebrocortical laser-doppler flow oscillations following inhibition of nitric oxide synthase.

Apparatus

• See the equipment chapter

Miscellaneous

• Yale veterinary anesthesia notes