Sevoflurane Flashcards
What is the MAC of sevoflurane?
2.0
What is the oil:gas partition coefficient for sevoflurane?
80
What is the blood:gas partition coeffcient for sevoflurane?
0.6
What is a partition coefficient?
The ratio of the amount of substance in one phase to the amount of it in another at a stated temperature.
When the 2 phases are in equilibrium and of equal volumes and pressures.
What is the blood:gas coefficient?
It’s a measure of the solubility of a substance in the blood and influences anaesthetic onset and offset times
How does solubility of volatile relate to it’s onset and offset?
The more soluble the volatile is, the slower it’s onset and offset.
This is because the effects depend on the partial pressure in blood and not the amount dissolved in blood.
What are the most soluble volatiles?
Halothane and isoflurane (low partial pressures in blood - therefore need more molecules required to saturate the liquid phase)
What are the least soluble volatiles?
Desflurane and sevoflurane.
Alveolar concentrations rise rapidly towards inspired concentrations, achieving higher partial pressures in alveoli, blood and brain, and onset of anaesthesia is more rapid.
What is the oil:gas coefficient?
Measure of lipid solubility. An indicator of potency.
It’s inversely related to MAC. So highly soluble agents are more potent and a lower MAC is needed
What is sevoflurane?
All the volatiles (except halothane and nitrous oxide) are halogenated ethers. An ether is a link between two carbon-containing compounds.
Sevo is a polyfluorinated isopropyl methyl ether (MW = 200). It has 7 fluorine atoms.
Ethers are lipid but not water soluble.
A halogen is a member of group 7 on the periodic table - fluorine, chlorine and bromine. Fluorine, being the lightest of the 3. The lighter the MW - the more blood soluble and less potent.
How are inhaled anaesthetic agents metabolised?
They undergo metabolism in the liver via the cytochrome P450 system.
The carbon-halogen bond releases the halogen ion which is potentially nephrotoxic.
The C-F bond is more stable and minimally metabolised.
The C-Cl and C-Br bonds are more easily metabolised.
What % of sevoflurane is metabolised?
3-5 % - into inorganic and organic fluorides
What CVS SEs will sevoflurane have?
- decreased SVR
- decreased MAP
- decreased HR
- CO maintained
- decreased myocardial contractility at high doses
- decreased myocardial work and O2 consumption
- is NOT dysrhythmogenic
- coronary steal is possible
What is the boiling point of sevoflurane?
58.5 degrees C
What is the SVP at 20 degrees celcius of sevoflurane?
22.7 kPa
