Q&A MAC calculations

  1. What concentration of Sevoflurane would you deliver to ensure surgical MAC if administering 50%N2O?



    BTW, are we starting new threads for each new topic or just identifying the new topic under this thread?
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  2. 12 Comments

  3. by   nilepoc
    I never heard back from anyone on this, but I vote for seperate threads for each topic.

    What do you all think?

    50% No2 is about .5 MAC, (actually .48) and the MAC 1 of Sevo is 2%. So assuming you are going for a MAC of 1 (50% of the population does not respond to surgical stimulus at MAC 1) a delivery of 1% sevo would be appropriate, as MAC is addititive.

    Craig
  4. by   nilepoc
    I accidentally fill a halothane vaporizer with isoflurane,

    I decide to do my case without knowing about the error, and set my output at 1.1% for a MAC of 1.5 of halothane. What MAC of isoflurane am I actually delivering?

    Other than using the wrong agent, would I still be safe, and why or why not?
  5. by   TexasCRNA
    Nile, not sure about the mixing of gases in the wrong container cuz the only three we use is iso, sevo, des and there is no way to mess up putting the wrong one in another container but I have switched gases in the middle of a case and will have both on the patient at the same time w/o problems except you have to remember that the two toegather are combined and you have to adjust or titrate to the patient response. The mac of iso is 1.15 so if you filled your contanier with only iso and set your dial to 1.1% then you are at mac.

    I like the idea that you suggest on Q&A title, to keep each topic seperate. We could cover the different topics and those with strengths in one area can help others and visa versa.

    There is so much to learn, review is always good.

    Lee
  6. by   TexasCRNA
    Also I think another good section would be to put things in a type of format labeled Clin Exp: title. As I do cases day in and day out I pick up little tid bits that help me learn and usually as a class we share these things to help others who may not of had a certain type of case or experience so that when they do have that type of case they will know what to expect and or some tip to make their life easier during the case.

    I don't know maybe this sounds like too much work cause we all have to keep up with our studies, classes, care plans and whatever else they deem students need to do.

    Lee
  7. by   WntrMute2
    Iso and halothane have very similar VPs so the output should be close. Too early for the math. You can cross fill any vaporizer except Des easily. Just fill a iso bottle with sevo for instance. Must be done on purpose but it can be done.
  8. by   nilepoc
    This is the kind of question my instructor loves. She practices in undeveloped countries a fair bit, and insists that we are proficient in figuring this kind of thing out.

    You are all correct in stating that the VP is similar, the MAC delivered though would be about 1 of isoflurane because its 1.2% for a MAC of 1. So now your patient would be recieving "less" anexthetic. We all know that we need to take into account Solubility and otherr factors to truly decide if less anesthetic is being given.

    Craig
  9. by   AL bug
    Very good nilepoc...you did not overdose your patient on Sevo. I had a test on the uptake and distribution of inhalation agents today. Did well. Getting ready for the 1st CV test on Monday.
  10. by   ufmatt
    hey guys. speaking of learning, what is MAC?

    by the way, i am a practicing RN in an open-heart ICU. I have only that silly little gre between me and CRNA school. Thanks,

    Matt
  11. by   WntrMute2
    Minimal Alveolar Concentration. It is the concentration of volatile agent required to keep 50% of the patients from moving with surgical stimulus. BTW guys, if MAC is ED50, what is ED 95 of agents? Also what is the procedure with the greatest requirement of agent to prevent moving?
  12. by   nilepoc
    ED50 is the effective dose for 50% of the population, I.e. MAC concentration, the ED95%
    is then 1.8 times the MAC.

    So a MAC of 2 would be 3.8% for ED95.

    And on the last bit, I will have to guess, Thoracic surgery?

    Craig
  13. by   WntrMute2
    hey Craig, we learned 1.6 MAC, but it wasn't a calculated number. So you may well be right. On the second part, laryngoscopy with intubation is considered more stimulating than surgical stimuli. Patients need the deepest level of hypnosis at that point.
  14. by   AL bug
    we learned surgical MAC (ED95) is 1.2-1.4MAC, but concentration depends on the agent of course.

    and with intubation, we were taught that MAC-bar (blocking adrenergic response to intubation) is 1.5MAC (but that is supposedly barring response for 99%-100% of patients)

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