Sevoflurane Flashcards
What is sevoflurane?
A prolyfluorinated isopropyl methy ether.
Achiral (unlike the other volatile agents)
Storage of sevoflurane
During storage where the concentration of added water is below 100ppm it is susceptible to attack by Lewis acids at its ether and halogen bonds, releasing the highly toxic hydrofluoric acid.
Lewis acid = a substance that accepts an electron pair. Includes many metal oxides but also H+- glass is a source.
HF acid errodes glass exposing sevo to further Lewis acids.
Sevo is therefore formulated with 300ppm of water (a Lewis acid inhibitor).
Stored in polythene napthalate bottles
Manufacture of sevoflurane
One-pot method: all ingredients mixed then water added to 300ppm.
Chloro-fluoro method: the basic molecular architecture is manufactured but with chlorine attached. This is then substituted with Flourine to produce sevo.
Respiratory effects
Pleasant odour. Depresses ventilation with a reduction in minute volume and rise in Pa CO2.
Cardiovascular effects
SVR falls and heart rate remains unchanged which leads to a fall in BP.
Cardiac contractility is unaffected and the heart is not sensitised to catecholamines.
Vascular resistance to both cerebral and coronary circulations is decreased.
CNS effects
Compared with halothane, there is evidence that children exhibit a higher incidence of post op agitation and delirium, which may extend beyond the initial recovery period.
How is sevo metabolised?
Cytochrome P450 (isoform 2E1) to a greater extent than the others apart from halothane.
Hexafluoroisopropanol and inorganic F- (renal toxic) are produced. F levels above 50 don’t show renal toxicity unlike in methoxyflurane as no renal metabolism.
Toxicity of sevo
Compounds A-E identified when sevo used with CO2 absorbents.
A and B are detectable and less toxic.
Formation favoured by potassium hydroxide > sodium hydroxide based absorbents particularly when dry. Reaction produces heat and consumes sevo.
Nephrotoxic level of compound A is 150-200ppm.
Molecular weight
200.1
Boiling point
58.5
SVP at 20 degrees (kPa)
22.7
MAC %
1.80
Blood: gas partition coefficient
0.70
Oil: gas partition coefficient
80
Odour
Non-irritant
