pharmacology- inhalational agents Flashcards
What class of agents are desflurane and sevoflurane?
fluronated ethers.
The fluorination increases potency and decreases the substances flammability.
what is the meyer overton principle?
increased lipid solubility is associated with increased potency.
This was originally described as its ability to dissolve in olive oil.
What is the mechanism of inhaled anesthetic agents?
The Majority theory is that inhaled agents exert their effect by binding directly to ion channels, this action varies depending on the channel that is bound.
1) enhance inhibitory ion channels (GABA, glycine) (more chloride ions influx)
2) block the function of excitatroy ion channels (NMDA) (less sodium and calcium influx)
3) also augments the release of neurotransmitters
what is a MAC?
what are some its variants.
minimum alveolar concentration. - different percentages of partial pressures for different agents depending on their potency.
1.0 MAC= 50% of people will not respond to a surgical stimulus via a skin incision.
MAC awake- 0.33 MAC= 50% of p[eople will not wake to their name being called.
AD 95- 1.3 MAC= 95% of people will not
MAC BAR- (block adrenergic response) - 1.5 MAC
What is the vapour pressure, blood gas solubility and % of metabolites for sevoflurane?
What is the vapour pressure, blood gas solubility and % of metabolites for desflurane?
What are some of the factors that effect MAC?
no effect- gender, ethnicity, duration, decerebarate.
Decrease MAC- co administration of anaesthetics.
pregnancy
chronic amphetamine use, acute alcohol
hypothermia
metabolic acidosis, hyponatraemia.
Increase MAC
chronic alcohol
acute amphetamine use
hyperthermia
MAOId
hypernatraemia
what would happen to an sevoflurane vaporiser at 6000 feet altitude.
vapour pressure = 157 mmHg
at sea level pressure =760 at 6000 feet altiture atmosphertic pressure= 610mmHg
157/760= 21%
157/610 = 26%
If the dial was at 2.1% - 1/10 of vaporiser gas being delivered. so 2.1% delivered at sea level, this means the same setting would deliver 2.6% sevo at altitude. but this is a partial pressure,
so the actual amount delivered is 2.6% x 610mmhg = 15.86mmHG
vs 2.1% x 760 mmHG= 15.96mmHG.
what would happen to an desflurane vaporiser at 6000 feet altitude.
desflurane vaporizers deliver the dialed in percent adjusted to the atmospheric pressure.
so at 6000 feet- atmospheric is 610mmhG, so a dial at 10% will give 61mmHG of des vs at sea level it will deliver 76mmHg.
