Anaesthetics

RE: Anaesthetics

catsrule — Fri, 22 May 2015 11:32:39 GMT

Thanks everyone some great ideas we will definitely put some of your advise into practice. The soda lime was changed a week ago and we have checked the circuit tubes. Will keep a check on the ET tubes and definitely try get some refresher training on this machine. We use fluosorbers-they are kept out of the bag and weighted weekly. The Labrador has since been seen at a referral practice and had a successfully anaesthetics that went with no complications.

RE: Anaesthetics

fairy — Fri, 22 May 2015 09:30:54 GMT

Just a thought... are you checking how far the ET tube is going? It may be going a little too far down.

Pulling it out slightly and checking dead space may help.

RE: Anaesthetics

David Beattie — Fri, 22 May 2015 09:19:28 GMT

Hi Catsrule - below are some rambling thoughts I had on reading your post that may or may not be worth reading As you've been at this for quite some time, I suspect that you have probably thought about all these points already, but I can't think of anything else more helpful...

[quote user="catsrule"]circle circuit[/quote]

What brand/type?

Definitely leak-proof?

[quote user="catsrule"]initially just oxygen for a few minutes depending on how deep they are[/quote]

Part of your problem may relate to excessive propofol given too fast - but it sounds like that is not the case - as you are aware, if propofol is given too fast can cause apnoea (having an iv cannula in place generally stops vets giving propofol too fast in my experience). I wouldn't generally want a patient to be induced with propofol so deep that it was then placed only on to oxygen ONLY - this may also cause a problem as the propofol will start to wear off and the patient won't have been receiving isoflurane (which takes some time to reach effective brain concentrations from when you start breathing it), at which stage it will then become "light", "sense" the isoflurane and "breath-hold" much as if you were trying to gas it down with a mask.

If I was to suggest trying a single change it would be to put the patient on to approx 2% isoflurane from the start, giving time for the isoflurane to be breathed in and reach effective brain concentrations before the propofol wears off to avoid the sort of "see-saw" effect you seem to be experiencing at this stage if I've understood correctly. If light and hyperventilating with shallow-breaths, I'd bag the patient with deep breaths every 6 to 10 secs for a couple of minutes while assessing its depth.

If the patient is not breathing after propofol (or is not breathing enough), then bag them as otherwise not only will they not be getting oxygen, but they will not be getting isoflurane. Approx one "breath" every 10-15 secs is usually sufficient at this stage.

[quote user="catsrule"]We start on 4 l/min oxygen reduce it to 1-2 l/min.[/quote]

These levels may be excessive depending on you set-up, but unlikely to be the cause of your problems. It may be important to make sure that when you change the dial for iso percentage that you empty the bag and let if refill by turning the flow up if required so that the percentage in the bag that the patient is breathing is actually the same as the percentage on the dial - especially if using a 2L bag. AVOID the oxygen flush valve to fill the bag up unless you want pure oxygen (you likely do, but I've seen some nurses use this mistakenly on a new machine thinking that it simply speeds up the FGF while it is actually bypassing the isoflurane...)

[quote user="catsrule"]On nearly every anaesthetic the dogs start to hyperventilate then breath hold for a while till we can stabilise them .[/quote]

[quote user="catsrule"]On two other occasions both during dentals on elderly dogs they were stable, breathing fine until we turn them over then they start hyperventilating, turned blue and then breath hold before eventually settling down.[/quote]

I'm guessing these are 2 different problems. With the first one, see above where my guess is you are probably not getting the iso on board before the propofol wears off, but a cannister leak or other equipment issue is certainly possible.

On the second one: turning patients during dentals causes massive physiological changes and is a good reminder why it's always super-important to check a patient thoroughly after repositioning or moving them under anaesthesia. They may just have been a little "light" and the stimulation of turning them caused them to wake-up a bit, but "turning blue" would make me think this was not the whole picture. The "bottom" lung in a patient under anaesthesia will collapse from air as time passes -> this leads to less oxygen in it -> leads to a reduction in blood perfusion by the clever lungs that realise this -> you flip the patient over and then what was the top lung that was keeping the patient oxygenated now gets squashed at the bottom before the new top one has a chance to expand with air and figure out that it now needs to majorly switch around the blood perfusion of the lungs -> these are big physiological changes and in an elderly patient that may have underlying heart/lung/other pathology the effects can be exacerbated. I would "bag" such a case with a breath every 6 secs or so if this happened until settled down. Also make sure that are disconnecting the ET tuibe from machine before turning so that not rubbing round the trachea or getting kinked etc. Also watch to turn in such a manner that fluid does not run down throat (and use a throat-pack to stop this etc).

[quote user="catsrule"]We usually pre med with acp and buprenodale and induce with propofol.[/quote]

Obviously fine, but some issues can occur in some patients - may be relevant in the odd elderly dental with pre-existant pathology:

ACP will cause clinically-relevant peripheral vasodilatation which means that more of the blood supply is going round the skin (which is not particularly important and doesn't need the extra blood, indeed this can just speed up heat loss from the patient) and this can make it harder to maintain blood pressure - if you measure blood pressure in anaesthetised patients you will see this and can give a fluid bolus, otherwise you could be missing it on occasions. I'd swop the ACP for midazolam in an otherwise calm older patient (as older patients are more likely to have pathology) or one with known relevant disease.

Buprenorphine takes a good 20-40mins to reach full pain-relief effects, so make sure not being given too little (or too much) time between adminstration and start of something painful under GA. For more painful things, use of local anaesthetics in addition and/or use of stonrger opioid such as methadone might be considered (but note that methadone can cause reduced breathing and heart rate if you're unfamiliar with it)

Swithcing propofol to alfaxan would cost a LOT more but might give you smoother indcutions with less hypreventilation and breath-holding. Given you've been at this a long time and only recently experienced problems, I doubt this is the fix you need.

[quote user="catsrule"],we turned the isoflo up ,it had no effect[/quote]

See above about making sure that what is being breathed is what you have dialled, also if shallow panting breaths then will not be getting the isoflurane into the lungs and therefore will not be reaching brain etc - bagging the patient with deep breaths of maybe 4-5% isoflurane for a minute or less should usually be sufficient, but you then need to watch that doesn't get too deep. Having said that, for the patient waking up in front of you, nothing is quicker than a bolus of induction agent (administered under vet's direction only obviously) and is a great reason for having an iv cannula in place and the remainder of your induciton dose handy.

[quote user="catsrule"]My thoughts are it the anaesthetic machines.[/quote]

If there is a leak or the isoflrane vapourizer is not correctly calibrated, then this could certainly be the case. Equally, a leaking bag, capnograph, tubing, cannister, ET tube or anything else allowing room air to reach the lungs.

RE: Anaesthetics

catsrule — Thu, 21 May 2015 14:01:46 GMT

[quote user="lindsay clapham"] Do you have a capnograph? [/quote]

No unfortunately we do not have a capnograph.

RE: Anaesthetics

Nick Shackleton — Wed, 20 May 2015 21:27:31 GMT

Maybe keep your patients on a higher flow rate for a bit longer before reducing oxygen rate. Do you have access to capnograph as this will give you any idea of what's going on all. Also suggest that you get you vapourisers service/Calibrated. Also as others have suggested check circuits and soda lime. Also are your tubes well cuffed. Best way is to put an ear to the patients mouth and gentle give a breath. If you hear air you know your cuff ain't inflated enough. If they are breathing around the tube threat will dilute your already diluted fresh gas flow. I would definitely recommend some monitoring equipment that will give you a better idea of what's going on. Also remember that Hanoi disconnect ie turning over during dental treatment it's advisable to increase fresh gas flow back up a bit Until patient settles down again

RE: Anaesthetics

lindsay clapham — Wed, 20 May 2015 20:32:06 GMT

Without being there it is obviously difficult to say for sure but I would recommend checking your circuits/tubing thoroughly for cracks e.t.c. Also check the Isoflurane tech is sat on the back bar correctly as Isoflurane will not be delivered to the patient if it is not.

Concentrations of volatile agent will take time to build up in rebreathing systems so the concentration you set on the dial may not be what is being delivered to the patient. So your patients may be lighter than you think. Also if they are breath holding or apnoeic they are not receiving oxygen or volatile agent so that could explain the sudden waking up and cyanosis.

Following induction I start on 2L oxygen and set Iso to 1%. I check a pulse and check for spontaneous breathing. If apnoea has occurred I IPPV but continue to provide low amount of Iso unless as long as the patient has good peripheral pulse quality. This allows a smoother transition between induction and general anaesthesia. Once spontaneous breathing occurs I increase the Iso if required. Do you have a capnograph? Looking at chest/bag movement does not give us a great assessment of tidal volume and effective ventilation.

RE: Anaesthetics

Sarah Bolton — Wed, 20 May 2015 17:47:07 GMT

Perhaps it may be worth also ventilating them until they are breathing better? If they're hyperventilating they will not be getting sufficient o2 or iso delivery. Also worth doing if the patient is only taking a few breaths as the tidal volume may not be sufficient??

RE: Anaesthetics

James Colver Cert. Ed, RVN — Wed, 20 May 2015 14:23:46 GMT

Priming the circuits first is a good idea. Do you use fluosorbers or similar? If so, make sure that they are completely unwrapped from their plastic bag before use. Also, ensure that your scavenge tube doesn't rise above the height of the patient (just some thoughts since you mentioned the cyanosis) - it would be good to have a capnograph hooked up if you have one.

RE: Anaesthetics

Jill Macdonald — Wed, 20 May 2015 13:15:14 GMT

Hi there,

We were having very similar issues with our semi-closed system (Burtons - upright canister setup). We had the rep come over and go through things with us, and basically the issues were being caused by not 'priming' the system enough. You need to have, say, 2% iso (or whatever leve you need), and 4L of oxygen for at least 10 minutes in order to ensure that this is what is actually being delivered to the patient. Then the O2 can be reduced to 1L. She suggested using the valve on 'just off open'. Then of course, if you move from prep to theatre, and a different machine/system/circuit, you need to 're-prime' that circuit, and that's where our issues were occurring as we were getting them stable, and then moving to theatre, and with the added insult of starting surgery they were becoming light and waking up.

All the signs you have given (although the cyanosis is a litlle worrying) suggest to me that the patients are in too olight a plane of anaesthesia, and then painful stimuli are highlighting this. Apnoea (breatholding) can be a common result of this (which then means they don't take in iso and become even lighter!)

I would strongly advise that you ask whoever supplies your machine/circuits to come and give you a refresher on use of the systems.

I'd also suggest checking all the tubing (we were using co-axial and changed to parallel so that it's easier to detect if there's an issue), ensuring Iso levels are on 'full' on the machines, and getting the vaporisors checked/recalibrated, and as someone else has said, ensuring the soda-lime isn't exhausted.

It might be worth also making sure you have another 'backup' system to use of you're having probs, such as a lack or bain.

Hope this helps..

Jill

RE: Anaesthetics

alice456 — Wed, 20 May 2015 12:38:31 GMT

The only thing that I can think of is to look at when the soda lime in the circle cannister was last changed as if it is full it will cause rebreathing CO2, Hope this helps, sorry I can't help more.

Alice