Pharmacology of Inhaled Anesthetics Flashcards
(42 cards)
ideal inhaled ansthetic
- stable shelf life without preservatives
- compatible with existing equipment
- inexpensive, non flammable and easy to vaporize
- low blood solubility
- high potency
- minimal CV and resp depression
- good muscle relaxation
common inhaled anesthetics
- isoflurane
- sevoflurane
- desflurane
all are ethers
important physical properties of inhaled anesthetics
VAPORS, not gasses. 1 exception is nitrous oxide: it is a gas at standard temp and pressure
- saturated vapor pressure: amount total, constant for each individual liquid (mmHg)
- boiling point: temp of liquid where all of it will get converted into a gas
there is some amount of agent floating above the liquid
what is the exception to inhaled anesthetics being vapors and not gasses?
nitrous oxide: N2O: it is a gas at standard temp and pressure
why is desflurane less commonly used?
it boils at room temp! need to keep it at a temp above boiling point to give a constant amount
what inhaled anesthetic has the highest partition coefficient?
isoflurane: 1.4 compared to others which are 0.45
what is a partition coefficient?
ratio that describes how a drug distributes itself between two phases (usually gas and a tissue/fluid) at equilibrium
common is blood/gas partition coefficient: How soluble the anesthetic is in blood compared to alveolar gas
what does a low partition coefficient mean?
= low solubility in blood = less uptake by blood and tissues. doesn’t want to hang out in blood: goes in faster and comes out faster; meaning faster induction and recovery
what inhaled anesthetic has a high partition coefficient?
isoflurane: 1.4. = 1.4x as much in blood than in gaseous state
compared to desflurane: 0.45: fast onset and recovery
which inhaled anesthetic has the lowest partition coefficient?
desflurane
why should a patient with kidney disease or at risk of kidney disease not get sevoflurane as an inhaled anesthetic?
because it is heavily metabolized/recovered as metabolites: 3% of it is. it has all these little fluorane groups that have to come off and get metabolized. not good to have F ions floating around
interacts with baralyme and forms Compound A, which makes the kidneys sad
what does sevoflurane get turned into that is the reason why it is avoided in KD pts?
Compund A: has many metabolites (F ions) that come off and need to get metabolized. Compound A makes kidneys sad
use iso instead! 0.17% metabolized compared to sevofluranes 3%
how do you dose inhalant anesthetics?
- volume percent (dose) ex 2% isoflurane (# on dial: amount getting delivered)
- pressure (ex 45mmHg sevoflurane): what the body “sees”
2% isoflurane = 2% of the total pressure
T/F: because of differences in barometric pressure, vaporizers in fort collins vs sea level will have different pressures administered to the patients
false: modern vaporizers are temperature and pressure compensated for sea level. even tho barometric pressure is lower at foco will still calibrate it to be the same as sea level
what is MAC?
minimum alveolar concentration to prevent gross purposeful movement in 50% of subjects exposed to a supramaximal noxious stimulus: 1/2 patients need MORE. this is just a starting point. allows us to compare across different inhaled anesthetics
- these are in VOLUME PERCENT
what is the MAC of isoflurane in the cat?
1.63
what is the MAC of isoflurane in the dog?
1.30
what is the MAC of isoflurane in the horse?
1.31
what is the MAC of isoflurane in humans?
1.15
what is the MAC of sevoflurane in cats?
2.58
what is the MAC of sevoflurane in dogs?
2.36
what is the MAC of sevoflurane in horses?
2.31
what is the MAC of sevoflurane in humans?
2.05
what drugs have a low MAC? what does this mean?
low MAC = high potency = need less drug to get desired effect.
Isoflurane, Sevoflurane have low MACs
