I just finished my first week of CRNA school and I have a question from pharmacology.

On the machine, what value (and what is the abbreviation for it) do you monitor when trying to decide if the anesthetic agent is in equilibrium throughout the blood. I understand the concept of PA(alveolar partial pressure), Pa(arterial partial pressure), and Pbr(brain tissue parial pressure) needing to be in equilibrium. My other question is: is PA measured end tidal, or do you assume that PI(inspired partial pressure) is always equal to PA?

I know these questions are probably pretty basic for you guys, but bear with me I'm a newbie.
Thanks

p.s. this question is coming from Basics of Anesthesia by Stoelting Chapter 8