Stephens anaesthetic apparatus

RE: Stephens anaesthetic apparatus

Evelyn Barbour-Hill — Sat, 15 Dec 2018 22:28:11 GMT

[quote user="Anthony Todd"]I'd like to understand the fixation on irrelevant agent %ages unless, as happened in the early days, the "experts" fixated on vapouriser %age until the relevancy was re -explained.[/quote]

The concentration in the inspired gas in the alveoli determines the concentration in the blood which determines the depth of anaesthesia.

That is the relevance.

You are quite right in that it is unnecessary to know that concentration as a number. It's also true that respiratory rate is another factor.

[quote user="Anthony Todd"]

All I know is that we tried to euthanise a patient by putting the vapouriser on full.

All that happened was the respiration rate slowed right down and the patient just remained very anaesthetised.....!!

[/quote]

Agreed.

RE: Stephens anaesthetic apparatus

Evelyn Barbour-Hill — Sat, 15 Dec 2018 17:03:45 GMT

[quote user="Michael Woodhouse"]I can have a wall mounted conventional anaesthetic machine, recon vaporiser in use for around £800. The semi disposable circuits are ~£15 and last us around 6 months. When I looked (admittedly 5+ years ago) in circuit systems were vastly more expensive and then spares (like tubing) similarly dear.[/quote]

Oh. OK. Though it may be a matter of comparing quality, rather than comparing type – I don't know. I reckoned that my anaesthesia apparatus was a fundamental necessity and was going to last a very long time so I would get what I considered best.

[quote user="Michael Woodhouse"]I looked at pictures and the machines seemed mucg bigger than the wall mounted ones? [/quote]

No. What takes up space is what it's mounted on, not the apparatus itself. You can easily wall mount a Komesaroff or a Stephens (Komesaroff is very compact indeed, and lightweight) and you don't have the 'tec vaporiser taking up space.

RE: Stephens anaesthetic apparatus

Anthony Todd — Sat, 15 Dec 2018 15:56:59 GMT

[quote user="robloxley"]Yes, at the vapouriser. Using low-flow techniques and rebreathing systems, which was what I was referring to, then the %age at the patient can be very different from the vapouriser setting.[/quote]

True of course, but the in-circle vapourisers are designed to allow for that; I suppose you could put a sensor just before the tube.

In fact I think Stephens did a lot of work with a Hook and Tucker and halothane to get the %ages he wanted.

And again, the same principle would apply unless you knew the tidal volume, so the result is meaningless.

I'd like to understand the fixation on irrelevant agent %ages unless, as happened in the early days, the "experts" fixated on vapouriser %age until the relevancy was re -explained.

All I know is that we tried to euthanise a patient by putting the vapouriser on full.

All that happened was the respiration rate slowed right down and the patient just remained very anaesthetised.....!!

RE: Stephens anaesthetic apparatus

Rob Loxley — Sat, 15 Dec 2018 14:30:31 GMT

[quote user="Anthony Todd"]Of course the patient is rebreathing the exhaled agent as well so your value will be lower than the actual intake anyway.[/quote]

I'm talking about using a capnograph that continuously samples the gas throughout the inspiratory cycle, at the ET tube connector

[quote user="Anthony Todd"]most [all?] vapourisers give an accurate %age anyway[/quote]

Yes, at the vapouriser. Using low-flow techniques and rebreathing systems, which was what I was referring to, then the %age at the patient can be very different from the vapouriser setting.

RE: Stephens anaesthetic apparatus

Anthony Todd — Sat, 15 Dec 2018 09:59:06 GMT

[quote user="robloxley"]If your monitor measures volatile agent than you can get an instant readout of exactly what % inspired iso/sevo the patient is getting - vapouriser in or out of circuit[/quote]

But that is meaningless if the animal isn't breathing, or hyperventilating/panting/gasping/ breathing fast [you know what I mean] and most [all?] vapourisers give an accurate %age anyway.

Of course the patient is rebreathing the exhaled agent as well so your value will be lower than the actual intake anyway.

https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular.../halothane

In people, the rate of metabolism of halothane is 20–25%. In other words, 75–80% of the inspired halothane is exhaled unchanged.

All I can attest to is that the in-circle vapouriser we used for many years with many operators gave trouble free anaesthesia over a vast number of different patients from tiny to huge at minimal cost, trouble and maintenance.

RE: Stephens anaesthetic apparatus

Michael Woodhouse — Sat, 15 Dec 2018 09:45:03 GMT

[quote user="Evelyn Barbour-Hill"]But cost?[/quote]

I can have a wall mounted conventional anaesthetic machine, recon vaporiser in use for around £800. The semi disposable circuits are ~£15 and last us around 6 months. When I looked (admittedly 5+ years ago) in circuit systems were vastly more expensive and then spares (like tubing) similarly dear.

[quote user="Evelyn Barbour-Hill"]And what do you mean by bulk?[/quote]

I looked at pictures and the machines seemed mucg bigger than the wall mounted ones? At the time we were in a tiny surgery and space was an absolute premium.

RE: Stephens anaesthetic apparatus

Rob Loxley — Fri, 14 Dec 2018 20:05:56 GMT

[quote user="Anthony Todd"]Minimum O2 requirement for a dog/cat is 6.6ml/kg/min. Therefore, it's recommended to use at least double, or 15ml/kg/min. for a totoal rebreathing system. If using a partial rebreathing system, 25ml/kg.min. (minimum setting should be 500 ml/min[/quote]

I'll happily go lower than 500ml/minute; most decent vapourisers are accurate down to about 200ml/minute and you can get low-flow rotameters for accurately setting a low flow rate.
What I wouldn't forget is that some sidestream sampling capnographs take a fair about of gas per minute - but then if you're using a capnograph you can keep a watch for rebreathing of CO2.

If your monitor measures volatile agent than you can get an instant readout of exactly what % inspired iso/sevo the patient is getting - vapouriser in or out of circuit

RE: Stephens anaesthetic apparatus

Anthony Todd — Fri, 14 Dec 2018 15:51:19 GMT

[quote user="bevs2251"]one vet (older than me, did a locum for him) as he was trying to tell me to run it at 1 Litre that it was a low flow machine and should hardly ever have to use it at more than 100mls flow rate, even for big dogs ! [/quote]

This helped me:

Minimum O2 requirement for a dog/cat is 6.6ml/kg/min. Therefore, it's recommended to use at least double, or 15ml/kg/min. for a totoal rebreathing system. If using a partial rebreathing system, 25ml/kg.min. (minimum setting should be 500 ml/min.)

The tidal volume is calculated at 10 to 20 mL/kg of body weight. ... Donna Knitter (philadelphia)

You get a guide anyway when the bag gets full [or empty....]

RE: Stephens anaesthetic apparatus

Anthony Todd — Fri, 14 Dec 2018 10:03:42 GMT

A friend had a major bowel resection and had a spinal tap and constant adjustable spinal pain relief with a syringe pump while recovering for 3-4 days and lying on the spine.

Routine, apparently, and the surgeon said the op could have been done just with a spinal.....

[I would have thought the risk on infection was high] but the post op pain was zero!!

RE: Stephens anaesthetic apparatus

Evelyn Barbour-Hill — Thu, 13 Dec 2018 23:38:31 GMT

[quote user="Michael Woodhouse"] Iso is very cheap so using a bit more of that (when you can get it) makes no appreciable difference to cost.[/quote]

We in-circle vaporisers are having a quiet chuckle presently at the plight of the isoflurane-wasters.......

[quote user="Michael Woodhouse"]The in circle systems seem to rely on the principal cause pain, breath more, go deeper.[/quote]

Well, I suppose one could use it that way,but I prefer to use it steady...... If something's going to be painful, we set a deeper steady state. More seriously, the point is that if the plane for any reason deepens too much, or for any other reason the patient slows its breathing too much or even ceases breathing, addition of the volatile agent to the inspired gas immediately reduces or ceases, instead of volatile agent constantly being further pumped in with the fresh gas flow.......

[quote user="Michael Woodhouse"]Cost. Familiarity. Bulk.[/quote]

Familiarity, of course. But cost? And what do you mean by bulk?

RE: Stephens anaesthetic apparatus

Oliver Morrison — Thu, 13 Dec 2018 12:14:20 GMT

talking of using local blocks - has anyone tried lumbosacral epidurals for abdominal surgery in dogs and cats. I use them for hindlimb surgery to great effect, lidocaine combined with an opioid. And very easy to do. Very nice and stable anaesthetic. I have used them for sheep caesarians. Lidocaine only last 60-90 mins, so animal is up and walking shortly after surgery. The opioid provides longer painrelief, and the local provides absolute analgesia during surgery. I have read about people using them for abdominal surgery in dogs and cats, but not yet tried it. Considering how cheap the drugs are, they are certainly worth considering. Yes there are risks, but if you are careful, and considering we do them all the time in cattle and sheep in dirty environments, in conscious animals, and get good results. In a clean clinic with an aneasthetised patient, that risk is considerably reduced surely.

RE: Stephens anaesthetic apparatus

Anthony Todd — Thu, 13 Dec 2018 10:11:35 GMT

[quote user="Michael Woodhouse"]Better idea of what your patient is getting (we don't have a circle for similar reasons).[/quote]

This is the old mistake and just shows a lack of logic but was propounded embarrassingly by anaesthetic experts too. "In-circle" machines deliver a reliable %age of O2 but unless you know the tidal or minute volume the %age is irrelevant; bit like drinking overproof rum while your mate drinks draught beer; depends on 'ow much and 'ow often...

[quote user="Michael Woodhouse"]We run O2 concentrators[/quote]

Fair point, but your use of anaesthetic agent, unused and finally collected, must be much more with out of circle vapourisers. The O2 flow rate, certainly with Fluotecs is unnecessarily high and way over metabolic needs also they need, or used to, servicing and recalibration every year?

PS we had great difficulty persuading staff to have one collection/delivery for 4 empties rather than a delivery/collection as each one was empty!!

[quote user="Michael Woodhouse"]I'd also rather keep the animal's pain managed [/quote]

This is the main unarguable point which I can't defend but can easily be nullified by pre-medication; many of these pain-relief drugs are only recently available and may be used. Pain during anaesthesia was not really considered BITD. But why don't the human surgeons propose it?

PS I Googled "pain relief during surgery" and ALL the links were for pain relief AFTER surgery, in humans anyway.

Surely human surgeons must have realised this concept UNLESS "an-aesthetic" does mean just that?

I wonder if users of in-circle vapourisers still get this raised tidal volume with pre-op pain-relief when the ovarian ligament is pulled?

[ Actually, despite many painful periods in many procedures, eg molar removal this only occurs when that ligament is pulled, ??]

Is it just some sort of reflex?

[quote user="Michael Woodhouse"]I like steady.[/quote]

This could mean that, most of the time the patient is deeper than necessary which the proponents of local anaesthesia in dentistry constantly expound.

If these in-circle systems are not satisfactory I am surprised that at least two pretty smart contributors on here are still proponents.

RE: Stephens anaesthetic apparatus

Michael Woodhouse — Thu, 13 Dec 2018 09:54:31 GMT

[quote user="Anthony Todd"]As an aside why do you think in-circle vapourisers like the Stephens and its successors aren't more popular as they, to me and a few others [on here] who I respect, are a rare breed and most vets use a Fluotec with all it's disadvantages?[/quote]

Cost. Familiarity. Bulk. Better idea of what your patient is getting (we don't have a circle for similar reasons).

We run O2 concentrators so there is no difference in oxygen cost whatever the flow rate (rural so cylinder delivery stupidly expensive). Iso is very cheap so using a bit more of that (when you can get it) makes no appreciable difference to cost.

We have 2 anaesthetic machines but at a guess we'd use both at once maybe 6 times a year. Not wirth the investment in 2.

I'd also rather keep the animal's pain managed with good analgesia and pre-med. I don't see the panting when pulling on ovaries in most animals, in the good old days with ACP pre-med they all did it. Medetomidine, pre-op NSAID seems to help massively.

The in circle systems seem to rely on the principal cause pain, breath more, go deeper. That's not how I like an anesthetic to go really. I like steady.

RE: Stephens anaesthetic apparatus

bevs2251 — Thu, 13 Dec 2018 03:10:38 GMT

Hated Stephens machine initially, especially with halothane (woudn't keep animals under 10kg asleep). Learnt to use it properly with isoflurane after watching a DVD on it. Loved it after that - think it's 4mls/kg flow rate. Had the large animal flow meter so think 50mls was lowest we could keep flow, even for ferrets. Worked great. Used hardly any gas with the low flow rate. Dead space is the issue - must have close fitting mask if masking down or keeping on a mask (rabbits for example). Had to explain to one vet (older than me, did a locum for him) as he was trying to tell me to run it at 1 Litre that it was a low flow machine and should hardly ever have to use it at more than 100mls flow rate, even for big dogs !

RE: Stephens anaesthetic apparatus

Anthony Todd — Wed, 12 Dec 2018 23:39:48 GMT

[quote user="Beats"]panting can involve only rapid, shallow, superficial "breaths" where air is going into anatomical dead-space such as trachea rather than alveoli. [/quote]

True, it does depend on the definition of "panting", taking yours, you are correct and long endotubes would add to it. My recollection is though that shall we call it the "pain reaction" panting when tugging on the ovarian ligament was deep enough, indeed it must have been, 'cos the patient deepened within a few breaths.

We used to cut the endotubes shorter as often, in the early days, a long one could end up only in one bronchi.....

As an aside why do you think in-circle vapourisers like the Stephens and its successors aren't more popular as they, to me and a few others [on here] who I respect, are a rare breed and most vets use a Fluotec with all it's disadvantages?

I have heard it said that it is because you don't know how much anaesthetic agent the patient is getting [nonsense of course, 'cos you don't know the minute volume even if you do know the %age in the O2].

We had a locum who wanted me to sign a disclaimer saying that, if using the Stephens, he could not be held responsible for anything untoward, so the perception was there.

RE: Stephens anaesthetic apparatus

Beats — Wed, 12 Dec 2018 22:40:16 GMT

[quote user="Anthony Todd"]

[quote user="Beats"]A panting patient can have, on occasions, less inhalant uptake.[/quote]

But this "panting" only happens [with me anyway] with tension on the ovarian ligaments ie before you have put your local in, I think?

Assuming the patient is tubed, the cuff is inflated and the vapouriser is not bypassed please tell me how it can have less inhalant uptake??

And assuming minute volume is increased, of course.

[/quote]

panting can involve only rapid, shallow, superficial "breaths" where air is going into anatomical dead-space such as trachea rather than alveoli. This is an effective means of evaporative cooling without causing hypocapnia in the awake and hot patient. [I'm not sure whether "panting" as I meant it, short and shallow, is the resp pattern one gets from tugging ovarian lig? it may be deeper, rapid breaths. Hence my qualification about "panting" and on occasions intended as more general comment]

If you increase minute volume by making a very large increase in respiratory rate, while decreasing the tidal volume to a point where the patient is "panting" (by this I mean taking very shallow, rapid breaths where the air inspired is not reaching the gas-exchange parts of the lungs such as alveoli), then the concentration of isoflurane reaching the blood may decrease. If you stick a long ET tube on and add significantly to the apparatus (and thus total) dead space, then the effect would be amplified. If you are using a vapourizer-out-of-circle device (as arguably most UK vets do?), then the concentration of inhaled isoflurane will not be increasing in the inhaled gas mixture with the increased respriration, so only the decreased effective gas exchange will be occurring (unless you increase the %iso on vapourizer); if you are using a VIC, such as Stephen's, then the concentration inhaled will increase and this may offset any decrease in effective ventilation of alveoli etc?

RE: Stephens anaesthetic apparatus

Anthony Todd — Wed, 12 Dec 2018 22:21:04 GMT

[quote user="Beats"]A panting patient can have, on occasions, less inhalant uptake.[/quote]

But this "panting" only happens [with me anyway] with tension on the ovarian ligaments ie before you have put your local in, I think?

Assuming the patient is tubed, the cuff is inflated and the vapouriser is not bypassed please tell me how it can have less inhalant uptake??

And assuming minute volume is increased, of course.

RE: Stephens anaesthetic apparatus

Beats — Wed, 12 Dec 2018 17:55:33 GMT

[quote user="Anthony Todd"]

Oh sure, I just wonder whether the obvious, what I called hyperventilation, actually did what you believe your lidocaine did?

This would happen with any inhaled anaesthetic, so your lidocaine effect is actually down to the anaesthetic's increased uptake, and therefore effect.

[/quote]

I have spayed bitches with and without lidocaine on ovarian pedicle. I have a personal preference for the latter.

A panting patient can have, on occasions, less inhalant uptake.

RE: Stephens anaesthetic apparatus

Anthony Todd — Wed, 12 Dec 2018 17:16:27 GMT

[quote user="Beats"]I appreciate there are many ways to spay a bitch[/quote]

Oh sure, I just wonder whether the obvious, what I called hyperventilation, actually did what you believe your lidocaine did?

This would happen with any inhaled anaesthetic, so your lidocaine effect is actually down to the anaesthetic's increased uptake, and therefore effect.

RE: Stephens anaesthetic apparatus

Beats — Wed, 12 Dec 2018 16:51:33 GMT

[quote user="Anthony Todd"]

[quote user="Beats"]I inject it into the ovarian pedicle with a 25G needle[/quote]

But the pain, or reaction, came when I pulled on the uterus/ovarian ligament to get to the ovary, or it did when I finally found the uterus ??

It was the stretching of the ligament which caused the bitch to breath "harder and faster" as it now should be referred to......

No reaction on ligating or cutting as I recall but, by then the bitch was deeper I guess; it seems like giving it after the pain has gone??

[/quote]

I follow.

If injecting with lidocaine, I lift it enough to give injection (and as you say can start to breathe faster doing that), then set down, do other one, come back to first and yank it out with force etc to do ligature etc.

You are quite correct that the pain comes on pulling the ovarian ligament, but if you don't pull it so far, give a quick injection and let go again it is much more brief and less severe than yanking it out to ligate it first time round.

It's my personal preference, I appreciate there are many ways to spay a bitch :-)

RE: Stephens anaesthetic apparatus

Anthony Todd — Wed, 12 Dec 2018 15:09:27 GMT

[quote user="Beats"]I inject it into the ovarian pedicle with a 25G needle[/quote]

But the pain, or reaction, came when I pulled on the uterus/ovarian ligament to get to the ovary, or it did when I finally found the uterus ??

It was the stretching of the ligament which caused the bitch to breath "harder and faster" as it now should be referred to......

No reaction on ligating or cutting as I recall but, by then the bitch was deeper I guess; it seems like giving it after the pain has gone??

RE: Stephens anaesthetic apparatus

Beats — Wed, 12 Dec 2018 14:50:57 GMT

[quote user="Anthony Todd"]Where and what do you do with the lidocaine and how much?[/quote]

Not more than 4mg/kg lidocaine in a dog total body dose if using.

I inject it into the ovarian pedicle with a 25G needle personally (be very happy with your spay technique and ligatures before doing), but you can squirt it on alternatively.

An alternative to deepening the level of general anesthesia.

RE: Stephens anaesthetic apparatus

Anthony Todd — Wed, 12 Dec 2018 13:52:52 GMT

[quote user="Evelyn Barbour-Hill"]Strictly speaking that's not hyperventilating, it's just breathing harder and faster[/quote]

So, of course, I googled "breathing faster and harder" and got on to sites that seemed to be restricted to adults, and had lots of large pictures of unusual views of people without clothes on.

Difficult, and a bit irrelevant, when under general anaesthetic I would imagine?

Ps I remember a client telling me that a skin lesion I was treating had "exhilerated".......

RE: Stephens anaesthetic apparatus

Anthony Todd — Wed, 12 Dec 2018 13:42:10 GMT

[quote user="Beats"]Not if you have the luxury of a few pence of lidocaine.[/quote]

Where and what do you do with the lidocaine and how much?

By the time I'd have put it where it goes respiration which became "faster and harder", therefore taking in a bit more agent, would have returned to normal...

PS Just realised this "faster and harder" breathing would happen with an out-of-circle open system too but I'll bet many twiddle with the vapouriser.....

RE: Stephens anaesthetic apparatus

Evelyn Barbour-Hill — Wed, 12 Dec 2018 12:58:07 GMT

Strictly speaking that's not hyperventilating, it's just breathing harder and faster.

I know, mere pedantry, but I had this morning yet another well-meaning owner saying the dog "keeps hyperventilating" – it was panting.

It's like "traumatic" and "haemorrhaging" and "in shock"..... they get it from ignorant journalists, I suppose.