Flashcards in Inhalational Agents Deck (26)
Potency is directly related to ________.
What is the Meyer-Overton Rule?
an increase in solubility = an increase in potency
What provides a "quantitative" measurement of lipid solubility?
the oil (olive): gas partition coefficient
What is the definition of a MAC?
the minimum alveolar concentration of an inhalational agent at which 50% of patients do not move in response to skin incision or similar noxious stimulus
MAC is inversely related to ________.
_______ is another way of representing lipid solubility, and therefore potency.
oil:gas partition coefficent
SO DO NOT GET CONFUSED---> SPEED OF UPTAKE is most represented by the _______ coefficient, and POTENCY is most represented by the ________ coefficient.
What agent has the highest blood:gas coefficient? What agent has the highest oil:gas coefficient?
HALOTHANE for BOTH
In regards to cardiovascular effects, what two IA's are primarily the same?
isoflurane and desflurane
both have slightly more decrease in BP and SVR than Sevo
What volatile anesthetic has no change in SVR?
What volatile anesthetic can produce none to a 20% increase in HR?
Isoflurane and Desflurane
What VA causes a sensitization to catecholamines?
Which VA has the least effect on BP and SVR?
The solubility of gas in a liquid ______ as temperature increases.
decreases (opposite of solids)
**More inhalational agent will dissolve if the patient is hypothermic--> LeChatelier's law
What determines the speed at which partial pressure of an agent builds up in the blood and subsequently the brain, and also determines the speed the agent is eliminated from the blood and the brain?
blood solubility, blood:gas partition coefficient
______ = blood solubility
______ = lipid solubility
The _____ the ventilation, the faster the uptake.
The ______ the cardiac output, the faster the uptake. (within limits)
Easy way to remember the Solubility graph for inhalational agents.
the graph represents the % that the agent is equilibrated after 30 minutes
*remember that Halothane was invented in the 50's.... then each IA for the next decade... 60's.... 70s... etc.
Don't forget that Enflurane will probably not be on the graph, but you must still use it for this to work!!
HE IS Doing Nothing
Halothane is 58% equilibrated after 30 min
Isoflurane is 73% equilibrated after 30 min
Sevoflurane is 85% equilibrated after 30 min
Desflurane is 91% equilibrated after 30 min
N2O is 99% equilibrated after 30 min
N2 is _____ times LESS soluble in blood than N2O.
34 times less
Compared with N2O, the carrying capacity of the blood for N2 is _____.
N2= 0.014 and N2O= 0.470
b\c of this difference, gas spaces change pressure or volume when N2O is turned on and off
*so normally the amount of N2 leaving the blood to the alveoli is the same that enter the blood from the alveoli, but since N2O is more soluble in blood, more can enter, thus more spaces distend
The rate of diffusion of gas into or out of the blood is proportional to its blood solubility. Who's law explains this?
Ficks law of diffusion
What law explains why gas bubbles distend when N2O is turned on or collapse when N2O is turned off?
Fick's law of diffusion
Explain the concentration effect.
With N2O turned on, the N2O diffuses into the blood quicker than N2 normal would, so the alveoli shrink in size thus permitting a more rapid uptake of N2O by the blood---> explained by FICK
Explain the second gas effect.
two anesthetics with varying onset speeds are given together--> a high concentration of a fast (N2O) with a slower second anesthetic gas.... the second gas achieves anesthetic levels more quickly than if it had been given alone