Inhalation Anesthetics Question

[mersault]

Question regarding inhalation anesthetics. On page 155 in Lange, it says: "the greater the uptake of anesthetic agent, the greater the difference between inspired and alveolar concentrations, and the slower the rate of induction."

This I find counter intuitive. Basically it's saying that if the blood takes up the gas quickly, it won't reach the brain, and we'll have a slower induction. How else can it get to the brain then through the blood? So does this mean, that if something has close to zero uptake by the blood then it will induce anesthesia faster (but it can't float through the neck/sinuses, etc up to the brain...the gas has to go through the blood).

Any help on this is appreciated.

-Mersault.

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[deleted9493]

There are multiple ways to think of this...

If you think about it at the compartmental level, you have a lung reservoir, a blood reservoir and a CNS reservoir. If you're using an agent that is more soluble in the intermediary blood reservoir, induction will be slower (the agent has a relative predilection to remain in the circulation). If, on the other hand, you are using an insoluble agent, the faster you can create a gradient between lung and CNS reservoirs and the faster your induction will be.

Another way of thinking of it is that blood soluble agents will be relatively diluted by the intermediary reservoir...(the blood because that is where it wants to stay). Again, if you can force a bigger gradient between the alveoli and the brain, the faster your induction will be...and that means using a drug that doesn't want to stay in the circulation.