Titration of Inhalational Agents

air · Nov 6, 2004

Oldsalt - I'm only in my first semester and haven't gotten to inhaled anesthetics ... I understand what MAC is, but would you mind defining MAC BAR for me? Thanks in advance.
Kat

Kat

MAC-BAR

For blocking adrenegic response usually about 1.5 MAC.

When I am with a not recent graduate (less than 7years) they usually prefer to get to MAC-BAR before first incision even with hemodynamics at 20-25% below baseline. I noticed hemos come back up with that first cut. I have been wondering if that has something to do with inadequate narcs onboard. We usually load with Fent. upfront.

athomas91 · Nov 6, 2004

i also like the high narc up front and titrated in at the end - but as far as gases - i would love to run them lower - however if you are not using nitrous (and i am picky who i use it with) then IF recall occurs you are up a creek.....it is i suppose the ART of anesthesia for a reason... :)

i was however just reading that with peds especially if you don't see that characteristic increase in HR with incision than perhaps they are too deep to the point of OD...i wonder if this is the case w/ adults as well...

i work w/ one anesthesiologist who feels that you should use narcs, low dose gas and beta blockers to take care of the ANS response... it actually works well - especially with older people.

keep teaching me guys!!!!!

Oldsalt · Nov 6, 2004

i also like the high narc up front and titrated in at the end - but as far as gases - i would love to run them lower - however if you are not using nitrous (and i am picky who i use it with) then IF recall occurs you are up a creek.....it is i suppose the ART of anesthesia for a reason... :)
i was however just reading that with peds especially if you don't see that characteristic increase in HR with incision than perhaps they are too deep to the point of OD...i wonder if this is the case w/ adults as well...
i work w/ one anesthesiologist who feels that you should use narcs, low dose gas and beta blockers to take care of the ANS response... it actually works well - especially with older people.
keep teaching me guys!!!!!

Thank you for your post.

In peds, with no changes in HR - I dont associate "OD" with that situation...Take for example a Normal Mask induction with Sevo - at which the child eventually becomes apneic, HR and BP decreases - This is not too deep - for peds - being too light and having a noxious stim (IV poke) can cause laryngospasm -Deep here is good -the End point is Not so much shooting for amnestic levels (whcih are always acheived) - we just want the tyke to stay still and stable.

IF ET % remains high where HR/BP continues to drop - than - yes - maybe a bit too much gas might be on board. Let off the gas a bit would be called for...

In the case for adults, again its finding where their own individual MAC BAR level is - for if you are over it - not only will get no response but you'll be treating that pressure and will continue to be an issue if you remain over it....

In regards to the previous question asked- MAC BAR, when described, should always be emphasized that it falls greater than normal MAC levels where 95% of the population does not respond to surgical stimuli (ie 1.2).

Additionally, Mac levels of 1.2 generally accepted in maintaining a patient in Stage 3

So the take away point here is (excluding the aforementioned cases in previous posts - trauma, emergent C-section, OH, etc..) that you are Over amnestic levels at MAC BAR. In other words - if their pressure is in the floor - they are most likely asleep/amnestic...

Well - what about the elderly who seem to just look at the vaporizer and get hypotensive...Lets look at this - Many of you who have been doing this have also seen what I am describing - minimal ET gases ( like .2 of Iso) =/- N20 and minimal Narcotics (ie. .25 - 1 mcg/kg Fentanyl) and still they require vasopressor support...A rule of thumb I follow is that MAC requirements decrease 10% for every decade after 60. Narcotics also decrease MAC requirements and significantly decrease MAC BAR by up to 50%.

So if you have an 80 y.o. - and you use 1 mcg/Fentanyl (up front) + N20 - You have a 70% reduction in surgical MAC - which for Iso is about an ET of .39 - and yes I have seen this many times

That's, Hence when you drive the ET up on these folks - well ephedrine, neo, epi gtt - you get the picture.

The use of Beta blockade is an excellent adjunct for the cardiac patients but can also play further havoc on you levels you are trying to maintain.

If I am overly concerned about possible recall d/t labile hemodynamics in a large blood case or similiar case - background propofol mixed with etomidate or versed , etc....can be added ....=/-the use of a BIS monitor.

In closing, this is an art - absolutely - wonderful isnt it?

Cheers

Athlein1 · Nov 6, 2004

Just my 2 cents. Turn off the poison gas and use more narcotics..You do not need a lot of inhalational agent/Nitrous for amnesia. Try using high narcotics (7-10 mics/kg of Fentanyl) even for a 30 minute case.

On the other hand, #1 - the one group of drugs that certainly cause PONV is opioids. Studies show that patients would rather experience pain than PONV. #2 - there is emerging evidence that high-dose narcotics, especially fentanyl and remifentanil, can induce a state called opioid-induced hyperalgesia. Just returned from the ASA meeting in Vegas, where it was in heavy discussion in some of the circles in which I eavesdropped. Several of these providers are using very low-dose narcotic (if any) on induction and titrating morphine at the end of the case with excellent results. Some of these providers also have a pre-emptive analgesia plan in place in their pre-op clinic (i.e. patient gets a cox-2 or NSAID, ultram, and decadron on AM of surgery). Others are using low-dose ketamine for pre-emptive analgesia (about 0.5mg/kg prior to incision). Very interesting. Expect more to emerge on this topic, as the evidence is striking, apparently.

WntrMute2 · Nov 6, 2004

On the other hand, #1 - the one group of drugs that certainly cause PONV is opioids. Studies show that patients would rather experience pain than PONV. #2 - there is emerging evidence that high-dose narcotics, especially fentanyl and remifentanil, can induce a state called opioid-induced hyperalgesia. Just returned from the ASA meeting in Vegas, where it was in heavy discussion in some of the circles in which I eavesdropped. Several of these providers are using very low-dose narcotic (if any) on induction and titrating morphine at the end of the case with excellent results. Some of these providers also have a pre-emptive analgesia plan in place in their pre-op clinic (i.e. patient gets a cox-2 or NSAID, ultram, and decadron on AM of surgery). Others are using low-dose ketamine for pre-emptive analgesia (about 0.5mg/kg prior to incision). Very interesting. Expect more to emerge on this topic, as the evidence is striking, apparently.

Correct me if I'm wrong, but I was taught that it is the initial exposure to opiods that cause N/V. In other words, once any narcotic is used, the amount doesn't really effect the incidence of PONV. Since somewhere along the way, most patients will recieve some opiod, I don't hold back. Anecdotally, I use way more fentanyl/Sufena/morphine than most of my collegues, and if anything my patients are puking less not more. Maybe because I didn't poison them with the purple gas. I also use N2O less frequently than most. When I give breaks I frequently see young women having GYN surgery, maybe a TAH with 100ug fentanyl, Iso @ 1.5% with 50% N20. No decadron, no Zofran. I'm throwing up just writing about it. If this were my case, I'd probably have 500 ug fentanyl, no N2O and 0.8% or so Iso. Decadron with induction and Zofran prior to closing. Morphine titrated in as respiratory rate is assessed. Many ways to skin the same cat.

snakebitten · Nov 6, 2004

You and I think alike, but again thats whats great about our job--we can do what we want

By the way are we ever going to get droperidol off the list and back on our carts

Correct me if I'm wrong, but I was taught that it is the initial exposure to opiods that cause N/V. In other words, once any narcotic is used, the amount doesn't really effect the incidence of PONV. Since somewhere along the way, most patients will recieve some opiod, I don't hold back. Anecdotally, I use way more fentanyl/Sufena/morphine than most of my collegues, and if anything my patients are puking less not more. Maybe because I didn't poison them with the purple gas. I also use N2O less frequently than most. When I give breaks I frequently see young women having GYN surgery, maybe a TAH with 100ug fentanyl, Iso @ 1.5% with 50% N20. No decadron, no Zofran. I'm throwing up just writing about it. If this were my case, I'd probably have 500 ug fentanyl, no N2O and 0.8% or so Iso. Decadron with induction and Zofran prior to closing. Morphine titrated in as respiratory rate is assessed. Many ways to skin the same cat.

Oldsalt · Nov 7, 2004

Correct me if I'm wrong, but I was taught that it is the initial exposure to opiods that cause N/V. In other words, once any narcotic is used, the amount doesn't really effect the incidence of PONV. Since somewhere along the way, most patients will recieve some opiod, I don't hold back. Anecdotally, I use way more fentanyl/Sufena/morphine than most of my collegues, and if anything my patients are puking less not more. Maybe because I didn't poison them with the purple gas. I also use N2O less frequently than most. When I give breaks I frequently see young women having GYN surgery, maybe a TAH with 100ug fentanyl, Iso @ 1.5% with 50% N20. No decadron, no Zofran. I'm throwing up just writing about it. If this were my case, I'd probably have 500 ug fentanyl, no N2O and 0.8% or so Iso. Decadron with induction and Zofran prior to closing. Morphine titrated in as respiratory rate is assessed. Many ways to skin the same cat.

Hi!

On this note....I am curious, if you could stratify the highest to lowest n/v triggers from personal experience - what would they be? And on that note if you could stratify the CTZ receptor in terms of what you think is the most important to least? I know the research - I am just curious what you think since you mentioned it in your post....

Regards

WntrMute2 · Nov 7, 2004

Hi!
On this note....I am curious, if you could stratify the highest to lowest n/v triggers from personal experience - what would they be? And on that note if you could stratify the CTZ receptor in terms of what you think is the most important to least? I know the research - I am just curious what you think since you mentioned it in your post....
Regards

It would be vary hard for me to say. I get almost no PONV except for open hearts where they are ofter somewat nauseated the next day. Young women getting GYN or breast surgery raises a big flag for me and I may add some benadryl early and 10 mg of propofol at the end. 5HT I believe is the most important with histamine being the least. Since I don't know the site of action of either propofol or decadron, I'm shooting at ghosts with those.

athomas91 · Nov 7, 2004

In peds, with no changes in HR - I dont associate "OD" with that situation...Take for example a Normal Mask induction with Sevo - at which the child eventually becomes apneic, HR and BP decreases - This is not too deep - for peds - being too light and having a noxious stim (IV poke) can cause laryngospasm -Deep here is good -the End point is Not so much shooting for amnestic levels (whcih are always acheived) - we just want the tyke to stay still and

ok - you need to correct me if i am wrong

but.... a normal mask induction the child becomes apneic in stage two - but rhythmic return of respirations is associated with the progress into stage 3 ... yes BP decreases but a HR decrease is associated with very bad things in peds because they are HR dependent for stroke volume and cardiac output as their sympathetic system is undeveloped and they are largely parasympathetic... so that a noxious stimuli like incision absolutely should cause an increase in HR and that IF that is blunted to the point of no response it is too much for them. ?!?! as well ...if muscle relaxant is utilized than movement should not be an issue after they are placed in stage 3 and an IV is secured during intubation... just my thoughts....

Oldsalt · Nov 7, 2004

It would be vary hard for me to say. I get almost no PONV except for open hearts where they are ofter somewat nauseated the next day. Young women getting GYN or breast surgery raises a big flag for me and I may add some benadryl early and 10 mg of propofol at the end. 5HT I believe is the most important with histamine being the least. Since I don't know the site of action of either propofol or decadron, I'm shooting at ghosts with those.

Thanks for your response.

Actually, N/V does have a link with the ANS hence our original discussion..but first the specifics so that we are all on the same sheet of music

I was fortunate to be the lead researcher, when in private practice, to do an in-house ongoing prospective study tracking the triggers and rates of N/V in an outpatient surgery center. After 1 year - we has complied over information on over 1200 patients, both genders, adult and peds - in cases ranging from ortho, ENT, GEN, and GYN.

While obtain and tracking the information (including.. but not restricted to: Case type, age, gender, NPO status, time in recovery, pretreatment, treatment after s/s, extended time for treatment r/t n/v, narcotic doses and time admin, voiding patterns, previous history, anesthesia tech., etc....)

In sharing this information with my group - we agreed to try differing methods to see its effect over a month and then rethink the approach the next based on the effect or ineffectiveness of our actions....We were all VERY familiar with all the research - but knowing that personal practice is 99% anecdotal and 1% research (i.e. you do only what you know and works)- we decided to do this approach...

What we found was we started with a rate of 30% (corresponding w/ the national average at the time - mid 90's) by the time we ended a year later the rate had dropped to less than 4% - Very impressive...

How did we do this? We ended up addressing very basic concepts in anesthetic approaches from the core understanding of the physiologic changes that N/V induces in the body.

Question: why do our patients have issues with n/v especially with inhalation agents (disregard case type and other qualifiers)? Because when looking at the changes that occurs w/ n/v (which has both a parasympathetic and sympathetic component) General anesthetic actually mimics these changes do they not (hence our discussion regarding MAC BAR)?

And its connection is here is in neurochemical control of vomiting. Mechanism of action is still being researched, peripheral neuroreceptors and the (CTZ - which have afferents are serotonergic, histaminic, dopaminergic, acetylcholine/muscurinic, Psychological, other suggest also opioids, and numerous other endogenous neurotransmitters) Where is the connection?

Acetylcholine/muscurinic ...which is connected to...the Vagus -

We noticed that by addressing issue of adequate fluid administration (i.e. patient voiding with first hour in recovery) - this is cannot to be overlooked, allowing for higher SNS tone (anticholinergics or in some cases IM Ephedrine of 25 mg generally blocking vagal response), good pain control, Selecting antiemetic with large CTZ covering (more later) and good education of pacu staff ( i.e.. no early increases in HOB or sudden movements - if patient becomes dizzy or nauseated - head down and a small fluid bolus) - generally really focusing blocking vagal responses.

For example - You mentioned Benadryl and decadron - well both work at Histaminic sites - but Benadryl also address other receptors - Muscurinic ( hence tachycardia, dry mouth, and increased SNS tone) and Psychological - sedative effects - so that combination works at 3 sites

Multiple coverage (in terms of sites) we found works the best - but after addressing the Vagal connection issue ( as mentioned above).

Well what about the sexy and expensive 5HTs? Well we didn't really use them unless really needed. My opinion is that we tend to be swayed a great deal to these reps telling us the this is the only route - which is not true. None of them that I have spoken with have any idea of what I just shared with you - nor will they share it if they did - why ? $$$$ Yes they work - but why do you have break through n/v with even these drugs? See above....

Take away point - stratify based on what we understand and are doing to the patient - areas that can be quantified and qualified - and treat them accordingly.

I Offer the following.....higher ANS tone in regards to watching MAC BAR - especially in emergence and recovery offers actually has more to offer than just intraoperative adjustments, amnesia, and haemodynamic control

Regards...

Cheers

BTW - this study was not published... unfortunately

Oldsalt · Nov 7, 2004

ok - you need to correct me if i am wrong
but.... a normal mask induction the child becomes apneic in stage two - but rhythmic return of respirations is associated with the progress into stage 3 ... yes BP decreases but a HR decrease is associated with very bad things in peds because they are HR dependent for stroke volume and cardiac output as their sympathetic system is undeveloped and they are largely parasympathetic... so that a noxious stimuli like incision absolutely should cause an increase in HR and that IF that is blunted to the point of no response it is too much for them. ?!?! as well ...if muscle relaxant is utilized than movement should not be an issue after they are placed in stage 3 and an IV is secured during intubation... just my thoughts....

Thanks for your question

In my explanation I was describing an induction -prior to IV placement- not maintainece of a peds patient (child) - not neo or infant. And absolutely - SV is fixed in those latter cases- but then age determinations must come into consideration in any patient --yes?---- Cook book anesthesia is not my fote.....But in a Allowing a Peds (Child) patient to breath them selves down to apnea is fine as long as it is not maintained - and this can occur in those vigorously crying patients frequently..IV placement prior to induction is ideal but not realisitic in many OP peds cases ----On a side note - Ive been in facilities where I had to both manage the airway w/ one hand and start a IV with the other - also not ideal - so a good supportive RN staff is very much apprecaited...I digress...

Lets go over this briefly:

Anesthesia is sometimes divided into stages and some of the stages are

further divided into planes.

Stage 1 =the period between administration of an anesthetic

and loss of consciousness.

Stage 2 or Delirium = the period after loss of conciousness. Characterized by :uncontrolled movement, delirium, breath holding, irregular respiration. Passing thru in induction and emergence is advised to as quick as possible ( hence my previous post)...Laryngospasm can occur at this stage on both induction or emergence

Stage 3 anesthesia is the level at which surgery can be performed.

Dividided into 4 planes...

Plane 1...Light anesthesia : blink reflexes and

swallowing reflexes are present and regular respiration with good chest motion.

Plane 2 : No blink reflexes, the fixed pupils, respirations regular

Plane 3: Respiration is shallow and adominal in nature- this is the "Surgical level" - which is maintained for control of pain

Plane 4 Breathing has stopped...

Stage 4:Crisis... too deep