Titration of Inhalational Agents

Oldsalt -

I have used but most regularly do not have a BIS monitor at my disposal - I go according to MAC but tailor it according to my patient and the needs that they display. I have worked with those who love it and those who feel it gives a false sense of security - I have seen the studies by BIS ....but who knows...:) IMHO

Oldsalt -

I have used but most regularly do not have a BIS monitor at my disposal - I go according to MAC but tailor it according to my patient and the needs that they display. I have worked with those who love it and those who feel it gives a false sense of security - I have seen the studies by BIS ....but who knows...:) IMHO

Thanks for your post.

The use of the BIS is not the qualifier but .....what MAC BAR levels for the inhalational agents are you seeing when you "Tailor it"? Hence what are you being taught the value of MACBAR vs. MAC when maintaining intraop. anesthetic levels using strictly inhalational agents (no backgroung propofol gtt - ie nv prevention) =/- N20 (hence always having ephedrine ready post induction / preincision)....or further ....what ranges would you expect to see ( or are being taught) with the addition of narcotics in the afermentioned example? Is this more of a academic question or one that has actual clincial value?

Finally, what is you technique in adjusting your vaporizer setting? I find that there is really no common "techinque" per se....many just turn on the vaporizers - shooting for MAC - or at least .8 - Hyptotension and mutiple doses of Ephedrine be damned

I am very curious what other peoples views are on this...

Thank you for your post and time.

regards

We do not have BIS monitors but have a couple PSA 4000 which is close to the same thing. I have only used it a couple times since we run way more rooms than have PSA monitors. I am still in school so I don't know everything but I try to run at least 1 MAC based on the patients age. If blood pressure does not tolerate it I either run Nitrous to compensate then run O2 N2O flows 50/50 or I use Neo or Ephedrine. I have never had to use multi vials of ephedrine. Usually with fluids, neo and ephedrine the pressure runs fine or at least how I feel comfortable. I do see some old farts just turning down the gas if hypotension occurs and sometimes I don't feel comfortable going that far down on the gas. They have been at it a while so possibly know more than I. All what you feel comfortable with

We do not have BIS monitors but have a couple PSA 4000 which is close to the same thing. I have only used it a couple times since we run way more rooms than have PSA monitors. I am still in school so I don't know everything but I try to run at least 1 MAC based on the patients age. If blood pressure does not tolerate it I either run Nitrous to compensate then run O2 N2O flows 50/50 or I use Neo or Ephedrine. I have never had to use multi vials of ephedrine. Usually with fluids, neo and ephedrine the pressure runs fine or at least how I feel comfortable. I do see some old farts just turning down the gas if hypotension occurs and sometimes I don't feel comfortable going that far down on the gas. They have been at it a while so possibly know more than I. All what you feel comfortable with

Thank you for your post...

What you are describing is very close to what I have been hearing from all the students I have queried about this....

And indeed, Age MAC variations are listed for Sevo, and maintaining MAC levels are important in ensuring an amnestic anesthetic.

Plainly speaking ..I am curious on what your views (or your current instructions )on MAC BAR vs MAC and its use in the clincial setting both from an amnestic and ANS control point of view.

Thanks for your time

the problem i have is according to who i am with -

i look at inhaled/exhaled values and not the dial - (because i find the differences to be great)

i have been with providers that are very honest about telling you to run MAC no matter what (BP sacrificing ... and use vasoactive drugs) because if they have recall YOU as the provider have NO excuse

then i am with others who -if BP falls) have be turn my agents well below MAC which makes me very nervous....i don't know if this helps?!?!

this is taking into account the differing MAC between ages.

the problem i have is according to who i am with -

i look at inhaled/exhaled values and not the dial - (because i find the differences to be great)

i have been with providers that are very honest about telling you to run MAC no matter what (BP sacrificing ... and use vasoactive drugs) because if they have recall YOU as the provider have NO excuse

then i am with others who -if BP falls) have be turn my agents well below MAC which makes me very nervous....i don't know if this helps?!?!

this is taking into account the differing MAC between ages.

Thanks for your Post

This is the quandary isn't it? How "low can you go?" w/o sacrificing the amnesia?

MAC levels are points, provided by research (an in some articles by plaintiffs case reports), which try to be all inclusive - but leave many searching for the best level w/o sacrificing patients stability and amnesia.

MAC BAR, on the other hand, is well supported - remembering that MAC BAR>MAC 1.2>MAC.

Relating again that Shangri-La is to maintain Stage 3. This to can be dangerous if applied exclusively (i.e. open hearts, emergent C Sections, and Trauma) where haemodynamic and dilutional variables equal very low anesthetic levels and possible recall/awareness.

But, those situations aside, try to notice at what level you are blocking ANS (remembering that volatile agents will decrease ANS output - hence leaving dials at the stops at high flows usually = OR high jinks ...lights flashing, chests thumpin, drugs pushing, and such)

What I tell my students, is that close monitoring of ET gases postinduction/preincision and noticing where ANS changes occurs gives them an idea of where the lower range of MAC BAR falls for that particular patient. Mac BAR is not static - added the increase Sympathetic tone with noxious stim- will increase it. Keep in mind that MAC BAR is ABOVE MAC (critical point)

Carefully applied increases in Agent (+/- narcotics) will then give one an idea of upper MAC BAR range.

There is no gestalt in the method that we use to titrate. But in close monitoring plus clear understand of what we administering - hemodynamics rarely change greater than 10%- hence the use of vasopressors is very low.

The surprising thing is the large range that is required (or not required) for the various patients that you see.

Again, this is just a loose rule - but clear understanding of it and clinical application provides one a very stable anesthetic course in many instances. No I dont advocate running people on .02 ISO - but in those low MAC instances - one must adjust to other non BP changing agents to maintain amnesia -

Cheers

Thanks for your Post

This is the quandary isn't it? How "low can you go?" w/o sacrificing the amnesia?

MAC levels are points, provided by research (an in some articles by plaintiffs case reports), which try to be all inclusive - but leave many searching for the best level w/o sacrificing patients stability and amnesia.

MAC BAR, on the other hand, is well supported - remembering that MAC BAR>MAC 1.2>MAC.

Relating again that Shangri-La is to maintain Stage 3. This to can be dangerous if applied exclusively (i.e. open hearts, emergent C Sections, and Trauma) where haemodynamic and dilutional variables equal very low anesthetic levels and possible recall/awareness.

But, those situations aside, try to notice at what level you are blocking ANS (remembering that volatile agents will decrease ANS output - hence leaving dials at the stops at high flows usually = OR high jinks ...lights flashing, chests thumpin, drugs pushing, and such)

What I tell my students, is that close monitoring of ET gases postinduction/preincision and noticing where ANS changes occurs gives them an idea of where the lower range of MAC BAR falls for that particular patient. Mac BAR is not static - added the increase Sympathetic tone with noxious stim- will increase it. Keep in mind that MAC BAR is ABOVE MAC (critical point)

Carefully applied increases in Agent (+/- narcotics) will then give one an idea of upper MAC BAR range.

There is no gestalt in the method that we use to titrate. But in close monitoring plus clear understand of what we administering - hemodynamics rarely change greater than 10%- hence the use of vasopressors is very low.

The surprising thing is the large range that is required (or not required) for the various patients that you see.

Again, this is just a loose rule - but clear understanding of it and clinical application provides one a very stable anesthetic course in many instances. No I dont advocate running people on .02 ISO - but in those low MAC instances - one must adjust to other non BP changing agents to maintain amnesia -

Cheers

One thing i try to do is have enough agent to maintain amnesia, usually between 0.6-0.8 MAC and have enough narcotic on board to blunt those pesky ANS responses. That way patients wake quickly as the volatile level drops but they remain comfortable. I start with 5 mcg/kg for all but the shortest cases or those who are very old. I do not hesitate to load a lot more narcotic early but don't gas them to death in that event. Works for me.

Sorta new to this board, but here is my two cents. We have 2 PSA 4000 monitors that rarely get used. Our experience is that you can get to the magical "amnestic number" and have them move on you. Until they can monitor analgesia I find it useless. Our department favors high narcotic doses and less poison gas, but with the 50/50nitrous/at least 1/4 MAC gas, the studies show that recall is rare.

Thanks for your Post

This is the quandary isn't it? How "low can you go?" w/o sacrificing the amnesia?

MAC levels are points, provided by research (an in some articles by plaintiffs case reports), which try to be all inclusive - but leave many searching for the best level w/o sacrificing patients stability and amnesia.

MAC BAR, on the other hand, is well supported - remembering that MAC BAR>MAC 1.2>MAC.

Relating again that Shangri-La is to maintain Stage 3. This to can be dangerous if applied exclusively (i.e. open hearts, emergent C Sections, and Trauma) where haemodynamic and dilutional variables equal very low anesthetic levels and possible recall/awareness.

But, those situations aside, try to notice at what level you are blocking ANS (remembering that volatile agents will decrease ANS output - hence leaving dials at the stops at high flows usually = OR high jinks ...lights flashing, chests thumpin, drugs pushing, and such)

What I tell my students, is that close monitoring of ET gases postinduction/preincision and noticing where ANS changes occurs gives them an idea of where the lower range of MAC BAR falls for that particular patient. Mac BAR is not static - added the increase Sympathetic tone with noxious stim- will increase it. Keep in mind that MAC BAR is ABOVE MAC (critical point)

Carefully applied increases in Agent (+/- narcotics) will then give one an idea of upper MAC BAR range.

There is no gestalt in the method that we use to titrate. But in close monitoring plus clear understand of what we administering - hemodynamics rarely change greater than 10%- hence the use of vasopressors is very low.

The surprising thing is the large range that is required (or not required) for the various patients that you see.

Again, this is just a loose rule - but clear understanding of it and clinical application provides one a very stable anesthetic course in many instances. No I dont advocate running people on .02 ISO - but in those low MAC instances - one must adjust to other non BP changing agents to maintain amnesia -

Cheers

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. You will be surprised at how quickly and smoothly your patient emerges when you turn the poison off. Besides narcotics are less tramatic to your hemodynamics. Lastly, remember that Neo and/or ephedrine are NOT benign drugs. If your having to use Neo/ephedrine even in small doses, fix the problem first --usually its something simple.

Good luck

We do not have BIS monitors but have a couple PSA 4000 which is close to the same thing. I have only used it a couple times since we run way more rooms than have PSA monitors. I am still in school so I don't know everything but I try to run at least 1 MAC based on the patients age. If blood pressure does not tolerate it I either run Nitrous to compensate then run O2 N2O flows 50/50 or I use Neo or Ephedrine. I have never had to use multi vials of ephedrine. Usually with fluids, neo and ephedrine the pressure runs fine or at least how I feel comfortable. I do see some old farts just turning down the gas if hypotension occurs and sometimes I don't feel comfortable going that far down on the gas. They have been at it a while so possibly know more than I. All what you feel comfortable with

Sorta new to this board, but here is my two cents. We have 2 PSA 4000 monitors that rarely get used. Our experience is that you can get to the magical "amnestic number" and have them move on you. Until they can monitor analgesia I find it useless. Our department favors high narcotic doses and less poison gas, but with the 50/50nitrous/at least 1/4 MAC gas, the studies show that recall is rare.

Thanks for you reply.

What you are describing is the variability that most patients will present w/i a normal case - i.e. peaks and nadirs of IV narcotics and levels swing of noxious stim - the "magical number" does move I find - but by marking (I.e.. noting) the MAC BAR ranges - swings are mild and rarely moderate. I am not correlating BIS numbers w/ noxious stim - pain and amnesia are separate issues - but can have an effect - which I will mention later. The key is finding the BAR levels which generally are greater than MAC values. Hence recall is unlikely.

I agree that Narcotic use can narrow (and lower) the range (research shows decreases MAC BAR by up to 50% for Des and ISO- but doses greater than 3 mcg/kg of Fentanyl have no further effects) ....but large narcotic use also has proved to lessen antiemetic efficacy.

Furthermore, by monitoring these levels - crossing below MAC BAR levels allow increased hemodynamics on emergence (not hyperdynamic mind you) tending to shorten emergence - lending to the interesting fact of BIS levels also increases w/ increased hemodynamics - narcotics dampen this effect.

Yes, I do use Narcotics - but tend to limit its intraop use until emergence. Very loose in this description of practice...everything is individualized...

Am, I suggesting that this is the only best technique? NOT AT ALL - I am just trying to understand my peers and their rationale of practice methods and I appreciate your time and attention to this question.

Regards

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

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.