Anaesthetic scavenging

Re: Anaesthetic scavenging

Anthony Todd — Sun, 28 Oct 2012 20:18:28 GMT

[quote user="robloxley"]what, with the cost of iso and oxygen...[/quote]

So where does the 100cc [or so] of O2 go when you've got a 5 Kg cat or dog??

Re: Anaesthetic scavenging

Rob Loxley — Sun, 28 Oct 2012 14:44:32 GMT

[quote user="Anthony Todd"]So you'd have to run a spill for anything under about 10Kg? [Not that that, in itself is such a disadvantage][/quote]

what, with the cost of iso and oxygen...

Re: Anaesthetic scavenging

Anthony Todd — Sat, 27 Oct 2012 15:51:51 GMT

[quote user="robloxley"]Our Penlon Sigma Delta is rated down to 200ml/minute[/quote]

So you'd have to run a spill for anything under about 10Kg? [Not that that, in itself is such a disadvantage]

Best I've heard of, but the Stephens will go down to less than 20ml/min. so you never need to run a spill.

Re: Anaesthetic scavenging

Rob Loxley — Sat, 27 Oct 2012 15:35:58 GMT

[quote user="Anthony Todd"] other vaporisers wouldn't produce stable [or any] vapour at such low flow rates!![/quote]

Our Penlon Sigma Delta is rated down to 200ml/minute

Re: Anaesthetic scavenging

Michael Woodhouse — Tue, 23 Oct 2012 21:54:48 GMT

[quote user="Anthony Todd"]

[quote user="Michael Woodhouse"]

RVC has a veterinary museum.....................

[/quote]

I'm trying not to take this personally with little success....

[/quote]

Wasn't meant personally. I'm not condemning them, I just don't understand them.

Re: Anaesthetic scavenging

Ian Mostyn — Tue, 23 Oct 2012 19:51:39 GMT

[quote user="Bob Russell"]Despite this we find it a brilliant circuit (semi) closed or otherwise![/quote]

No argument from me there. We only use the ADE or a Modified T-piece.

Re: Anaesthetic scavenging

Anthony Todd — Tue, 23 Oct 2012 14:16:54 GMT

[quote user="Evelyn Barbour-Hill"]You were taught wrong.[/quote]

'cos the teachers were taught that [probably] and they've never looked at it critically.

And it's too too simple and easy

[quote user="Evelyn Barbour-Hill"]anything a Stephens machine could possibly be useful for[/quote]

Just use it for safe, fool-proof anaesthesia would be a suggestion.

Re: Anaesthetic scavenging

Anthony Todd — Tue, 23 Oct 2012 14:09:58 GMT

[quote user="Hannah Wynne Richards"]That's a debate I'm more than happy to submit to a DVA holder for a ruling[/quote]

Me too, hope one jumps in.

I'll give a few Heads of Argument to give him or her a starting point.

1. The vaporiser is marked in 1/8 divisions not percentages of anaesthetic concentration.

This is always cited as some sort of indication that the vaporiser is not accurate and was done deliberately because, with a vaporiser in the circuit it is the minute volume that determines the anaesthetic mass entering the animal. If the vaporiser is out of the circuit then the %age is important as you must run a spill or the animal will explode!

The Stephens vaporiser delivers very constant percentages at very low flow rates [respiratory, of the patient!!]. This is a concept that anaesthetists find hard to grasp!!

2. The anaesthetists don't credit the low resistance of 2cms of water in the circle and can't credit you can get satisfactory concentrations of agent at such low flow rates.

And, of course, ask the many users who all say, if they used it for any length of time, that it was fine.

Sure, aesthetics not good, although the latest versions have fewer joints and pipes etc.

Very sensitive to leaks [if the patient is waking up then there's usually a leak] [no bad thing really...]

And you have to visibly check the soda lime by opening the canister, a good thing because of gas tracking with the sodalime looking fine 'cos the gas tracks out of sight and can mask an expired canister.

Are there any users out there with a long history of use who have adverse things to say about its use and function apart from it ain't cool in 2012??

Re: Anaesthetic scavenging

Bob Russell — Tue, 23 Oct 2012 13:51:33 GMT

[quote user="Gillian Mostyn"]

[quote user="Bob Russell"]If I suggested it was a truly closed system I was being inaccurate![/quote]

hahaha - alternatively you could describe yourself as being wrong. But you are a man, after all!

[/quote]

The (admittedly old) flow rate chart on the wall describes the ADE being used as a semi-closed (for under 10Kg) and closed for those over 10Kg. we use it as a semi-closed system much of the time but the manufacturers seem happy to call it a closed system!

If I was wrong so are the makers of the system! Despite this we find it a brilliant circuit (semi) closed or otherwise!

Re: Anaesthetic scavenging

Hannah Wynne Richards — Tue, 23 Oct 2012 13:44:34 GMT

That's a debate I'm more than happy tosubmit to a DVA holder for a ruling

Wynne

Re: Anaesthetic scavenging

Evelyn Barbour-Hill — Tue, 23 Oct 2012 12:33:20 GMT

[quote user="Hannah Wynne Richards"]

I've been racking my brains to think of anything a Stephens machine could possibly be useful for-I mean it's not just current new grads who think it's dangerous-we were taught that before some of them were born

Wynne

[/quote]

You were taught wrong.

Re: Anaesthetic scavenging

Hannah Wynne Richards — Tue, 23 Oct 2012 12:10:07 GMT

Wynne

Re: Anaesthetic scavenging

Anthony Todd — Tue, 23 Oct 2012 11:17:04 GMT

[quote user="Michael Woodhouse"]

[quote user="Evelyn Barbour-Hill"]By the way I still have the Stephens in a cupboard........ just in case, it may come in handy one day........ [/quote]

RVC has a veterinary museum.....................

[/quote]

I'm trying not to take this personally with little success....

Re: Anaesthetic scavenging

Michael Woodhouse — Tue, 23 Oct 2012 00:55:23 GMT

[quote user="Evelyn Barbour-Hill"]By the way I still have the Stephens in a cupboard........ just in case, it may come in handy one day........ [/quote]

RVC has a veterinary museum.....................

Re: Anaesthetic scavenging

Evelyn Barbour-Hill — Tue, 23 Oct 2012 00:44:01 GMT

[quote user="Anthony Todd"]Why is your vaporiser smarter?[/quote]

I meant smarter in appearance! And it certainly doesn't leak!

It's essentially the same as the Stephens but smoother and slicker and cooler-looking

I gather that strictly speaking I'm using it semi-closed. Well, OK, so it's semi-closed. I'd call it almost-closed. Is that an official term? I'm sure you could run it fully closed if you wanted to.

For me too the respiration flow is to all intents and purposes the flow rate over the vaporiser.

By the way I still have the Stephens in a cupboard........ just in case, it may come in handy one day........

Re: Anaesthetic scavenging

Anthony Todd — Tue, 23 Oct 2012 00:01:39 GMT

Evelyn, I'm still not clear.

Why is your vaporiser smarter? Except that the system allows for leaks which doesn't sound smart to me. Yours is therefore a semi-closed system.

We never run any "flow rate", certainly not in cats; the circuit is fully closed until the cat comes off iso and goes onto oxygen when the circuit is flushed.

We actually use the animal's respiration as our flow rate over the vaporiser and just add O2 to the circuit to keep the bag semi full as the O2 is metabolised.

There is a "trickle valve" which some of us use with big dogs really out of laziness as it means you don't have to add O2 all the time via the "flush valve".

I don't think we change the plastic circuit tubing very often or at all, [unless it's damaged], but I don't recall we've ever had any post anaesthesia respiratory infections.

Anyway we've certainly nailed an absorber to every iso or fluothane machine in the country, I hope!!

Re: Anaesthetic scavenging

Evelyn Barbour-Hill — Mon, 22 Oct 2012 22:05:40 GMT

[quote user="Anthony Todd"]Evelyn, can you run the Komsaroff at "respiratory "flow rates? Is the vaporizer in the circle??[/quote]

The vaporiser is in the circle, just like a Stephens (but smarter). In fact there are two vaporisers – I think the original idea was that you might want halothane in one and isoflurane in the other (not to be used both at once of course!) – but we have only ever used one.

What are "respiratory" flow rates? We use a minimal oxygen flow rate – we never go as low as 5ml/kg/minute though, always twice that at least, as a safety buffer. So, cats, 100ml/minute. Twenty pound dog, 100-200 ml/minute. Forty pound dog, 300-500 ml/minute. And so on. Maximum possible is 5l per minute, so there's more than enough for any patient.

There is no flowmeter, only a flow control. I expect that will bring down on me the wrath of those who are still dedicated to Boyle's machine.

The sodalime container seems adequately well designed. The circuit tubing is semi-disposable – at first I thought it a disadvantage, needing to buy new circuits periodically, but I soon came to see it as an advantage. The machine tubing must be a rich source of respiratory cross-infections in veterinary practice!

Re: Anaesthetic scavenging

Anthony Todd — Mon, 22 Oct 2012 20:11:59 GMT

http://www.anaequip.com/documents/Fresh%20gas%20flow%20table%20for%20The%20Humphrey%20ADE-circle.pdf

Minimum flow recommended is 300 ml/min. This allows for small leaks; in addition

some vaporizers become inaccurate below this flow.

From the above link. Why on earth would you have "small leaks", why any leaks at all....

And note the bit about "some vaporizers..." as I stated before.

Evelyn, can you run the Komsaroff at "respiratory "flow rates? Is the vaporizer in the circle??

Re: Anaesthetic scavenging

Gillian Mostyn — Mon, 22 Oct 2012 18:35:55 GMT

[quote user="Bob Russell"]If I suggested it was a truly closed system I was being inaccurate![/quote]

hahaha - alternatively you could describe yourself as being wrong. But you are a man, after all!

Re: Anaesthetic scavenging

Anthony Todd — Mon, 22 Oct 2012 17:12:04 GMT

[quote user="Bob Russell"]These were the figures given 10 years ago. things have moved on and most flow rates are 300ml.[/quote]

Depends solely on the ability of the vaporiser to produce a constant concentration of agent and I believe some require a higher flow than 300cc/min.??

One of the main reasons why the Stephens was knocked; other vaporisers wouldn't produce stable [or any] vapour at such low flow rates!!

Re: Anaesthetic scavenging

Bob Russell — Mon, 22 Oct 2012 09:47:51 GMT

[quote user="Gillian Mostyn"]

[quote user="Bob Russell"]with our ADE system (which we really like!) the gas flows can be unbelievably low.[/quote]

The manufacturers are pretty specific about what gas flows you should be using for your ADE. The minimum is about 500ml for a normal cat, going up to a max of 1l for a heathy large dog. This is a pretty low flow (which we are happily using - I love my ADEs) but is still significantly more than would be needed for a closed circuit such as the Stephens. (O2 requirement in a closed system is approx 5ml/kg! A cat is therefore likely only to need about 20ml!!!) I would be very surprised if you are using as little as this as the standard vaporisers don't work properly with such low flow rates. Also, like Wynne said, it would be very difficult to prevent your anaesthetic gas levels from getting far too high in a completely closed system.

Oh, and the ADE cannot be used as a closed circuit unless you have the peep valve screwed down - which you aren't ever supposed to do. The valve has been designed specifically to be used open - it is a very smart valve! Hence a semi-closed circuit!

[/quote]

These were the figures given 10 years ago. things have moved on and most flow rates are 300ml.

http://www.anaequip.com/documents/Fresh%20gas%20flow%20table%20for%20The%20Humphrey%20ADE-circle.pdf

If I suggested it was a truly closed system I was being inaccurate!

Re: Anaesthetic scavenging

Malcolm Ness — Sun, 21 Oct 2012 20:35:52 GMT

[quote user="Evelyn Barbour-Hill"]Anybody see the vicious circle here........................?[/quote]

We have used most circuits over the years but the "Vicious Circle" is a new one on me!

Re: Anaesthetic scavenging

Evelyn Barbour-Hill — Sun, 21 Oct 2012 16:48:01 GMT

[quote user="Michael Woodhouse"]

[quote user="Evelyn Barbour-Hill"]If new graduates have no working knowledge of in-circle vapouriser systems, that's a failing of the veterinary schools.[/quote]

I have never seen an in circuit vaporiser in the flesh. To be honest I wouldn't know where to start. That said with iso at less than £20/bottle and my cylinder rental costing more than the oxygen itself the cost of the O2 and iso actually very minimal in terms of our GA costs.

We manage quite nicely with a modified T piece and a parallel lack.

There is only so much that they can squeeze into the teaching at vet school. There's too much in the curriculum as it is. Simple fact is most vets in general practice don't use these circuits.

(Also afraid that is the case with dentistry - scale, polish and extract is about what happens in most practices. I still need to google what root planing actually is. I would have loved more cattle lectures at college, but appreciate there is just not the time.)

[/quote]

Ok, partial apology to the veterinary schools. Let me rephrase:

if new graduates think that in-circle vaporiser systems are dangerous rubbish, that's a failing of the veterinary schools.

[quote user="Michael Woodhouse"]Simple fact is most vets in general practice don't use these circuits.[/quote]

Anybody see the vicious circle here........................?

Re: Anaesthetic scavenging

Michael Woodhouse — Sun, 21 Oct 2012 16:08:44 GMT

[quote user="Evelyn Barbour-Hill"]If new graduates have no working knowledge of in-circle vapouriser systems, that's a failing of the veterinary schools.[/quote]

We manage quite nicely with a modified T piece and a parallel lack.

There is only so much that they can squeeze into the teaching at vet school. There's too much in the curriculum as it is. Simple fact is most vets in general practice don't use these circuits.

Re: Anaesthetic scavenging

Gillian Mostyn — Sun, 21 Oct 2012 15:33:43 GMT

[quote user="Mark Hedberg"]might[/quote]

or might not. Who knows.