IN circle anaesthetic systems

RE: IN circle anaesthetic systems

vs0u — Mon, 15 Jan 2018 11:10:41 GMT

[quote user="Anthony Todd"]

[quote user="Edward Jones"]but the rate of metabolism of isoflurane is practically zero (if not actually zero?!)[/quote]

Er, they breathe it out and then they wake up....

They require a constant inspiration of agent or they'll wake up!

[quote user="Edward Jones"]Inhalation agent is not consumed. What goes in the patient must come out.[/quote]

Exactly, which is why they're connected to a supply of agent constantly or they'll wake up

[quote user="Edward Jones"]Once at a steady state, the net movement of agent in/out of the patient is zero. [/quote].

Then how and why do they wake up; ever??

[/quote]

They wake up when you turn off the iso because it keeps coming out but no more goes in!

As long as the iso is on, they keep breathing it in at eg. 2% (and out at 2%) so a steady plane of anaesthesia is maintained. Whatever you put in gets breathed out at the same rate - they equalise, whether that's 0% or 5%

Breathing it out does not mean it's been metabolised

RE: IN circle anaesthetic systems

Beats — Wed, 10 Jan 2018 17:17:45 GMT

[quote user="Carl Gorman"]A recent paper also demonstrated that the Komessarofs were temperature resistant which allows them to comply the Practice Standards requirements.[/quote]

Maybe that's why the PSS inspectors never mentioned our Komie being an issue.

I could re-commission it and hang a large sign round it saying "practice standards scheme compliant" in time for the next inspection - if eye-catching, the ensuing conversation of enlightenment might distract from poking through some other aspect in too much detail

RE: IN circle anaesthetic systems

Carl Gorman — Wed, 10 Jan 2018 09:42:12 GMT

I do enjoy seeing vets discuss thinns. Always entertainingand often enlightening.

We use Mini Kim’s and ADEs. Because I wrote a review of the ADE many years ago, Prof Humphrey (yes, Saint Humphrey of ADE) came to my practice with much clever kit to determine how low a flow rate could be used safely in a range of animals. His tech measured all parameters including gaseous agents in great detail. NOt only did he demonstrate that the ADE was safe at very low flow rates, he also confirmed that the Komessarofs were safe and effective in our hands.

A recent paper also demonstrated that the Komessarofs were temperature resistant which allows them to comply the Practice Standards requirements.

RE: IN circle anaesthetic systems

Anthony Todd — Mon, 08 Jan 2018 15:07:37 GMT

[quote user="Evelyn Barbour-Hill"]Komesaroff for about 28 years;[/quote]

Sorry, I should have specified the Stephens, where the vapouriser setting is the same for any patient from a chihuahua to a horse although the O2 input will be obviously much different.....

RE: IN circle anaesthetic systems

Evelyn Barbour-Hill — Mon, 08 Jan 2018 14:30:57 GMT

[quote user="Anthony Todd"] the vapouriser setting is the same for a 1Kg cat as a great dane or a horse,[/quote]

Well, sorry, Anthony, I used a Stephens on and off for years but I have been exclusively Komesaroff for about 28 years; I can assure you that in the Komesaroff the smaller animal needs a higher setting. Maybe I confused matters by mentioning tidal volume. The smaller the animal, the less the rate of flow of gas over the surface of the volatile agent at the time of inspiration at a given setting, so the setting (which is a flow-partitioner) needs to be increased to send a greater proportion of the gas over the volatile agent.

[quote user="Anthony Todd"]The hard thing was to stop anyone increasing the vapouriser setting if the animal hyperventilated as, by increasing minute volume, a greater mass of anaesthetic was absorbed.[/quote]

Indeed so. But they soon get the hang of it, as with any unfamiliar piece of equipment.

RE: IN circle anaesthetic systems

Anthony Todd — Mon, 08 Jan 2018 13:13:27 GMT

As an aside, once as a student I [among others] inhaled ether and nearly passed out...

Trouble was as I recovered the ether was breathed out and everyone could smell what I'd been up to!!

Emphasises the principle i was desperately trying to get across!

RE: IN circle anaesthetic systems

Anthony Todd — Mon, 08 Jan 2018 12:55:16 GMT

[quote user="Edward Jones"]but the rate of metabolism of isoflurane is practically zero (if not actually zero?!)[/quote]

Er, they breathe it out and then they wake up....

They require a constant inspiration of agent or they'll wake up!

[quote user="Edward Jones"]Inhalation agent is not consumed. What goes in the patient must come out.[/quote]

Exactly, which is why they're connected to a supply of agent constantly or they'll wake up

[quote user="Edward Jones"]Once at a steady state, the net movement of agent in/out of the patient is zero. [/quote].

Then how and why do they wake up; ever??

RE: IN circle anaesthetic systems

Edward Jones — Mon, 08 Jan 2018 08:42:07 GMT

[quote user="Anthony Todd"]

You said:

[quote user="Gillian Mostyn"]The animal is breathing out anaesthetic at the SAME RATE as it is breathing it in. [/quote]

And I a bit too harshly, but, I thought, correctly said

"Oh dear, in that case why does it go to sleep??" [you did SHOUT...]

Because the animal would breathe out anaesthetic minus the mass of anaesthetic it absorbed, so it would breathe out less than it breathed in.

[/quote]

What??? Inhalation agent is not consumed. What goes in the patient must come out. Whilst it is in the patient, and if at a sufficient concentration the patient is anaesthetised. Once at a steady state, the net movement of agent in/out of the patient is zero. It's not like we're topping up with a injectable, in which case the agent is actually 'consumed' (or rather, metabolised into a non-active form) - but the rate of metabolism of isoflurane is practically zero (if not actually zero?!)

RE: IN circle anaesthetic systems

Anthony Todd — Sun, 07 Jan 2018 22:35:14 GMT

[quote user="Evelyn Barbour-Hill"]the smaller the animal, the smaller the tidal volume so the higher the setting required for the same vapour concentration).[/quote]

No, sorry ithe vapour concentration will be the same independent of tidal volume [if you like]. The animal will absorb the same mass of anaesthetic per body weight which is why the vapouriser setting is the same for a 1Kg cat as a great dane or a horse, although the minute tidal volume will be, obviously, vastly different!

We never had to adjust the vapouriser setting provided the animal was anaesthetised; adjustment was only ever made in very high or very low ambient temperatures, and then only occasionally.

The animal made some adjustment itself by varying tidal volume eg when pressure on the ovarian ligament or after a period of apnoea.

The hard thing was to stop anyone increasing the vapouriser setting if the animal hyperventilated as, by increasing minute volume, a greater mass of anaesthetic was absorbed.

Not another one star, please, it just shows you can't understand.

RE: IN circle anaesthetic systems

Anthony Todd — Sun, 07 Jan 2018 22:17:32 GMT

[quote user="Evelyn Barbour-Hill"]Ah, the Komesaroff doesn't have such a thing. When I had a Stephens, I always understood that that was there for use with ether.[/quote]

No the sleeve could be used, when fully down, to mask induce but I only ever used it thus very occasionally.

RE: IN circle anaesthetic systems

Evelyn Barbour-Hill — Sun, 07 Jan 2018 21:26:03 GMT

[quote user="Edward Jones"]Don't you find that the majority of patients have an adequate plane of anaesthesia on 1.75-2% iso?[/quote]

I find that the vast majority of patients, after initial induction, are steady on the required plane of anaesthesia on the 1/4, 1/2 or 3/4 mark. (Which mark, depends on the plane required and on the size of animal: the smaller the animal, the smaller the tidal volume so the higher the setting required for the same vapour concentration). If they are not, due to individual variation, the setting has to be turned up or turned down, just as it would be with a fresh-gas-flow vaporiser system. Before we take it to be due to individual variation, yes of course we check for any malfunction or fault or miscalculation, just as you would with any other system. If we want to deepen the plane or lighten it for certain parts of the procedure, we turn the setting up or down, just as you would....

We don't monitor minute volume but we do monitor respiratory rate, just like we all do I presume.

[quote user="Anthony Todd"] in-circle machines have been misunderstood since their first introduction [/quote][quote user="Anthony Todd"]they are just so sensible easy cheap and reliable and foolproof, if used correctly.[/quote]

Yep. Well, not sure about fool-proof. The fool can kill a patient with just about any system if they try hard enough.

[quote user="Anthony Todd"]The sleeve on the vapouriser can, over time or inadvertently, slip down and should be checked, and pushed right up, each time more agent is added.[/quote]

Ah, the Komesaroff doesn't have such a thing. When I had a Stephens, I always understood that that was there for use with ether. I never used that. I used the bottle marked "halothane" which of course had no sleeve. I've used ether quite a lot in the past, and methoxyflurane at vet school (never saw it anywhere in practice); and chloroform once or twice, but that's another story.

RE: IN circle anaesthetic systems

Anthony Todd — Sun, 07 Jan 2018 18:03:59 GMT

You said:

[quote user="Gillian Mostyn"]The animal is breathing out anaesthetic at the SAME RATE as it is breathing it in. [/quote]

And I a bit too harshly, but, I thought, correctly said

"Oh dear, in that case why does it go to sleep??" [you did SHOUT...]

Because the animal would breathe out anaesthetic minus the mass of anaesthetic it absorbed, so it would breathe out less than it breathed in.

I can't think of any other understanding of what you said and what I said, not having a go for fun or malice, but in-circle machines have been misunderstood since their first introduction and even now, it seems.

Sad because in my, and other hands, they are just so sensible easy cheap and reliable and foolproof, if used correctly.

[One of my ex-colleagues said to me rather dolefully after he set up on his own that "the Stephens wasn't so bad". He's got some sort of fluotec machine....

RE: IN circle anaesthetic systems

Gillian Mostyn — Sun, 07 Jan 2018 17:48:24 GMT

[quote user="Anthony Todd"]Oh dear, in that case why does it go to sleep??[/quote]

Are you actually serious?

I give up.

RE: IN circle anaesthetic systems

Anthony Todd — Sun, 07 Jan 2018 17:25:17 GMT

Gee. I wish one-star person would explain where I'm wrong otherwise I'll just go on in ignorance and the rest of you will never get it right!

Arlo. I'm quite happy to be one-starred if I'm rude or offensive!

Mind you, as was always the case, and the reason why incircle vapourisers were condemned as unsafe even, amazingly, given the two large shiny CO2 adsorbers, that CO2 would build up, was that most people just couldn't understand the principle of circle systems.

RE: IN circle anaesthetic systems

Anthony Todd — Sun, 07 Jan 2018 16:55:35 GMT

[quote user="Gillian Mostyn"]The animal is breathing out anaesthetic at the SAME RATE as it is breathing it in. [/quote]

Oh dear, in that case why does it go to sleep??

[quote user="Gillian Mostyn"]In a rebreathing circuit the anaesthetic levels will be difficult to quantify[/quote]

You could easily measure the percentage of agent inspired but the point missing is you don't know the volume of inspired gas plus agent unless you know the tidal or minute volume in exactly the same way as my lager and gin analogy....

RE: IN circle anaesthetic systems

Gillian Mostyn — Sun, 07 Jan 2018 16:27:33 GMT

[quote user="Anthony Todd"]

So if you overventilate an animal, but only at the maintenance %age of say iso, the animal will not be in any danger and will not deepen beyond that "maintenance %age of agent via a vaporiser?

Is that what you're saying ie an animal cannot absorb a greater mass of anaesthetic agent than the %age ofagent being delivered no matter what the minute volume of agent plus O2 etc via excessive ventilation??

If you are your patient will be in trouble sooner or later......!

[/quote]

You are using your knowledge of your rebreathing circuit to extrapolate to others, which is not going to work.

Most of us use a non-rebreathing or semi rebreathing circuit. The animal is breathing out anaesthetic at the SAME RATE as it is breathing it in. Therefore hyperventilation will simply reduce the time it takes for the level to be reached. After that, it will equalise.

(If anything, it is likely to be going lighter because it isn't respiring properly and the dead space gases will be a higher percentage of the inhaled gas!!)

In a rebreathing circuit the anaesthetic levels will be difficult to quantify, as, like you said, the expired anaesthetic gases are almost all kept in the system. Thus I can understand your point about marking % on the dial being pointless.

RE: IN circle anaesthetic systems

Anthony Todd — Sun, 07 Jan 2018 11:52:15 GMT

PS One thing which is important and hasn't been mentioned yet:

The sleeve on the vapouriser can, over time or inadvertently, slip down and should be checked, and pushed right up, each time more agent is added.

RE: IN circle anaesthetic systems

Anthony Todd — Sun, 07 Jan 2018 11:34:29 GMT

Trouble is, with a closed circle,[like Stephens] the patient is rebreathing the expired air containing expired anaesthetic, but minus CO2, and because the tidal volume [minute volume] varies and is unquantified knowing the %age is meaningless, and I never bothered about it.

On 3/8 on the vapouriser would keep the patient nicely in a surgical plane for as long as you like without change, once surgical plane had been reached, but MA can probably tell you what that %age that was, 'cos I think his vapouriser has the %age marked.

Certainly, if there is even a small leak in the circuit they would wake up....... [usually a leak in the cuff on the tube!!]

We did try, on cases that were PTS because of exlap findings, to euthanase by putting the vapouriser on full but, surprisingly, these animals just kept breathing [although not as often....]!!

That gave me, and others, enormous faith in the safety of the Stephens because quite often nurses, and even vets, had not the most basic understanding of the machine or it's principle.

Similarly drip pumps and X-ray machines!!

RE: IN circle anaesthetic systems

Edward Jones — Sun, 07 Jan 2018 11:16:02 GMT

[quote user="Evelyn Barbour-Hill"]

[quote user="Edward Jones"]There's a great deal of point in knowing the percentage because that's the steady state the patient will end up at.[/quote]

What's important is the steady plane of anaesthesia the patient will end up at. By all means set your fresh-gas-supply vaporiser to 1.7598342% if that's what it "should" be, but you will still have to turn it up if the anaesthesia is too light or down if it's too deep.

[/quote]

Indeed, the percentage has to be individually tailored to the patient and situation, but 1) you have to have a preconceived notion as to what percentage will be required, and 2) if the required percentage seems to be particularly far from what you expect, I would ensure I am able to properly explain the reason for this (e.g. to ensure there isn't a malfunction or circuit fault).

Don't you find that the majority of patients have an adequate plane of anaesthesia on 1.75-2% iso? If I need something significantly outside of this for prolonged periods I'm trying to find out why, and 4 times out of 5 there's a good reason (that either needs correcting, or taking into account in future decisions).

[quote user="Anthony Todd"]The analogy is fine![/quote]

No, it's not - because when you imbibe, you're not also immediately excreting - at least, the rate of excretion is vastly lower than the rate ingestion. Alcohol excretion mechanisms are quickly overwhelmed such that the excretion rate of alcohol is constant regardless of the level in the blood. Drink twice as much and it'll take twice as long to be excreted. Inhaled agent, on the other hand, if there is adequate ventilation, is constantly exchanging, and the rate of exchange depends on the concentration gradient.

If minute volume is so critical presumably you monitor/calculate it constantly? How do you do this? I was never taught it to be necessary and I've never met an anaesthetist who thinks it is.

RE: IN circle anaesthetic systems

Anthony Todd — Fri, 05 Jan 2018 18:17:51 GMT

[quote user="Edward Jones"]There's a great deal of point in knowing the percentage because that's the steady state the patient will end up at. [/quote]

Just so I'm sure I understand you....

So if you overventilate an animal, but only at the maintenance %age of say iso, the animal will not be in any danger and will not deepen beyond that "maintenance %age of agent via a vaporiser?

If you are your patient will be in trouble sooner or later......!

[added when no answer to my questions]

And a PS You keep drinking your low alcohol draught beer pint by pint and I'll just have a few sips of my spirit and I'll walk out and even drive.

The analogy is fine!

RE: IN circle anaesthetic systems

Evelyn Barbour-Hill — Fri, 05 Jan 2018 18:01:44 GMT

[quote user="Edward Jones"]There's a great deal of point in knowing the percentage because that's the steady state the patient will end up at.[/quote]

RE: IN circle anaesthetic systems

Edward Jones — Fri, 05 Jan 2018 14:03:03 GMT

[quote user="Anthony Todd"]

[quote user="Michael Woodhouse"]Agreed. I like to be in control. I like to know what % inhalational the patient is getting, how much oxygen.[/quote]

Ah, another favourite trotted out by those who, frankly, [sorry[, don't grasp the basics!

What is the point of knowing the % in the inspired agent if you don't know the minute volume of the inspired gases?

eg. I'll sip neat gin all night while you down 8 pints of lager. My alcohol percentage is 10x, yours is 1x, but you've had 10 pints and I've had 2 G&Ts.....

[/quote]

This analogy is flawed. Ingestion is not inhalation. The analogy only holds during the very early stages of starting inhalational anaesthesia (i.e. before any appreciable amount of agent has built up in the blood).

There's a great deal of point in knowing the percentage because that's the steady state the patient will end up at. Of course the minute volume is important - it affects how quickly this steady state is achieved - but if the respiration is sufficient, or with IPPV if the patient is hypopneic then it's not particularly relevant.

RE: IN circle anaesthetic systems

Anthony Todd — Fri, 05 Jan 2018 02:03:19 GMT

[quote user="Evelyn Barbour-Hill"]keep on oxygen till anaesthesia very light; but I'd rather remove the tube before the patient actually "bucks" it or coughs it![/quote]

Um, this happens when anaesthaeia is very light... only reason we left it in was [rarely happened, actually] if you'd forgotten a tooth or a stitch or a wart, you were still able to gas them down and if for some reason, the animal stopped breathing etc. you could easily blow up the cuff and oxygenate.

As I've said before the only drama was on induction and/or when someone had the vapouriser on full when the patient was well under with thio or propofol ie anaesthetic overdose.

RE: IN circle anaesthetic systems

Evelyn Barbour-Hill — Fri, 05 Jan 2018 01:41:38 GMT

[quote user="Beats"] running a patient on 100% O2 is not necessarily desirable[/quote]

Of course "medical oxygen" is not 100% O2 anyway..... (irrelevant aside, I know... )

[quote user="Beats"]Propofol (or indeed etomidate) doesn't last very long. Your patient will wake up if you don't give it time to get iso on board[/quote]

Plenty of time with propofol. We always start with vaporiser off.

[quote user="Anthony Todd"]Machine disconnect and breathing air when last stitch, cuff deflated.[/quote]

There we differ, I like to turn vaporiser off when approaching "last stitch" time, empty bag and refill with oxygen, keep on oxygen till anaesthesia very light; but I'd rather remove the tube before the patient actually "bucks" it or coughs it!

Pulse oximeters are like the films of Alfred Hitchcock. Wildly over-rated.

RE: IN circle anaesthetic systems

Evelyn Barbour-Hill — Fri, 05 Jan 2018 01:25:34 GMT

The dead space is the length of the trachea (can't help that) plus the length of tube beyond trachea (cut that short whatever system you are using) plus the adaptor and Thermovent (if you use one) and connection up to the end of the co-axial tubing. Hard to see how you could make that any smaller (except by going to a T-piece, grant you that).

IPPV: Well in most circumstances of apnoea you would have turned the isoflurane off and refilled the bag with oxygen, surely? Three ways of operating the APL valve: i) just keep it shut, ii) keep it open just a tiny bit, iii)alternately open and close it. The choice is yours and might depend on circumstances.

If you want to IPPV with vapour on, as in open chest surgery (I have done many diaphragmatic hernias, and a few other things) you have a little think and usually keep the vaporiser on the lowest setting, while carefully observing depth of anaesthesia (you'd be doing that anyway, surely?)

Saliva? There's something pretty wrong if you are getting saliva in the vaporiser! I top up every day. Sometimes between ops too.

Moving to another machine in another room: I don't know. I've never wanted to do that. I'd say that when you transfer, if you don't put more oxygen in the bag than necessary, it will only be a few breaths before everything is stabilised exactly as it was. Unless you take too long about the transferring, but then that would upset any system.

Masking: I don't understand you. Assuming the mask is well fitting, you can induce anaesthesia.

Tricky to keep a large patient on just oxygen? Again, I don't understand. At the end of the procedure you turn the vaporiser off, empty the bag and refill with oxygen. If the bag empties too quickly for your liking, turn the oxygen flow up and open the APL a bit. I don't see the difficulty.

"Most of your new staff will not be experienced with an in-circle vaporiser..."

Wouldn't you expect to train (either briefly or extensively, as necessary) new staff, on all your machinery, anyway? They might not be experienced with something else, either. They might not be experienced with anything.

"19 year old cat getting all its teeth and thyroid out" ()

And yet..... my ancient cats or overweight pugs having prolonged procedures.... do just fine. So it's preference and familiarity but I'd abandon them if they brought adverse effects.

The Komesaroff has very little resistance to respiration. Granted, a total-non-rebreathing system has less than anything which has a CO2 absorber.

To increase rapidly the inhaled vapour concentration: Turn vaporiser up, empty bag, put the minimum of oxygen back into it. For slightly less rapid effect, just turn the vaporiser up.

Using intermediate settings on the Komesaroff vaporiser: You could if you wanted. I've never found a need. Sometimes we switch at intervals between, say, the first mark and the second mark. Works fine for us. Your nurse should be monitoring depth of anaesthesia all the time anyway and fine-adjusting, sorry, asking permission to fine-adjust, as necessary. Don't you do that with any system? A safety factor is that if anaesthesia becomes too deep then respiration is depressed so vaporisation is reduced, in contrast to the vaporiser in the fresh gas flow that continues to pump vapour in.

Denitrogenation? Yes you can, very easily. We do it every time before starting. It combines very well with leak-testing. Unless I've misunderstood what you mean by denitrogenation.