Tangent anaesthetic monitoring: pulse oximetry

RE: Tangent anaesthetic monitoring: pulse oximetry

Arlo Guthrie — Mon, 27 Jul 2020 15:39:16 GMT

Just back from staycation, and great to see the newly tweaked tangent button being used to discuss a point raised in the Expert Help Forums. Thanks Michael Woodhouse - I owe you a bottle for that. If you'd rather something other than champagne, then send me a PM.

My impression as a non-vet is that it works quite well doing things this way (anyone raise your hand if you disagree!). What I mean is that this looks like quite an interesting and useful discussion to have, and it also shows how the expert help forums can be a source of interesting discussions ...

I think I just now need to make it clear on the Expert Help Forum that that's what the tangent button is for (unless you are not in an expert forum, when its for just going off on a tangent in the same forum).

RE: Tanget on anaesthetic monitoring

Bob Russell — Sun, 26 Jul 2020 13:21:56 GMT

We use a capnograph for almost every procedure. We have an ancient Datex monitor that cost about £100 on ebay years ago. We have an all singing, all dancing one that talks to a computer. We have taken it out of its box but I like the old machine and watch it out of the corner of my eye. Beeps and alarms only when things seem not right.

Six anaesthetic machines, six capnographs IMO!

RE: Tanget on anaesthetic monitoring

Glen McIntosh — Sat, 25 Jul 2020 14:36:57 GMT

[quote userid="7232" url="~/001/veterinary-clinical/small-animal/anaesthesia/f/discussions/29247/tanget-on-anaesthetic-monitoring/224531#224531"]The problem is many of these guidelines are produced in Ivory towers. They’re not always practically useful on the front line. [/quote]

In many instances I would agree with you, but not in this case.

The recover guidelines are eminently implementable and practical for day to day practice.

I am very much “front line”, as it were, and in my current role I am often performing CPR several times a week. I will admit to being quite a bit skeptical when I first heard about the RECOVER guidelines (CPR is a bit like driving, we all think we are fantastic drivers and everybody else drives like a numpty, and that certainly there isn't anything anybody can teach us about driving), and tbh I wasn’t overly impressed when I was trying to read them. But then I was fortunate enough to be able to attend a RECOVER certification course. It was an eye opener and extremely useful and practical, and backed up by the best clinical evidence that is available to us in veterinary medicine, along with sound theoretical principles. It is one of the very few CPD courses that I have ever attended that has made a demonstrable difference to the way I practice and a demonstrable difference to the outcomes of that practice.

I recommend the RECOVER certification course as essential CPD for all vets in small animal practice, and go so far as to say that if you haven't done it then, no matter what you might think or how experienced you might be, you are probably not providing the best CPR for your patients that you potentially could be.

My experiences with CPR are mostly limited to emergency patients and very sick in patients. For me, though, an otherwise healthy patient arresting during anaesthesia for a routine or elective procedure would be a situation that is even more dire than the types of CPR cases I routinely deal with, so I wouldn’t have any qualms in getting someone from one of the other concurrently running GA’s to grab the ETCO2 machine.

But better still, invest in at least one good multi parameter monitor with ETCO2. If you’ve got 6 anaesthetic stations then you should be able to afford it?

And go do the RECOVER certification course, and I am certain you will “get” what I am banging on about. And then get all your staff (including all the nurses) to do it as well.

RE: Tanget on anaesthetic monitoring

Mark Holmes — Sat, 25 Jul 2020 13:42:45 GMT

[quote userid="3585" url="~/001/veterinary-clinical/small-animal/anaesthesia/f/discussions/29247/tanget-on-anaesthetic-monitoring/224525#224525"]Pulse oximetry is not advocated as a useful monitoring tool during the actual CPR since motion artefact makes pulse oximetry readings inconsistent and misleading, and the length of time in between rounds of chest compressions are usually not long enough for the pulse ox to start giving accurate readings (unlike ecg), even if there was a spontaneous return of circulation.[/quote]

That’s all ok if you have a capnograph. We don’t we also have 6 anaesthetic stations and may have several anaesthetics running concurrently and with limited “hands” I wouldn’t be sending someone to disconnect the capon and reconnect it during an emergency.

The pulse ox is easy to find easy to set up and if you see SPO2 increase from 70% to 98% it’s a good thing. It cannot be a bad thing.

The accuracy is very questionable but a good number is a good sign. They tend to be intermittent but read low.

The problem is many of these guidelines are produced in Ivory towers. They’re not always practically useful on the front line.

RE: Tanget on anaesthetic monitoring

Glen McIntosh — Sat, 25 Jul 2020 11:57:51 GMT

[quote userid="7232" url="~/001/veterinary-clinical/small-animal/anaesthesia/f/discussions/29247/tanget-on-anaesthetic-monitoring/224502#224502"] only really rate them for resuscitations. If the pulse ox can find a pulse, get a reading and it’s anywhere near 100% then the resus must be going ok. They are so shit that a decent score is a very very good sign. [/quote]

Just to mention, the current RECOVER guidelines for small animal CPR advocate ETCO2 as the primary and best method of assessing the efficacy of CPR, and in particular the efficacy of chest compressions. ETCO2 gives real time feedback about how effective your chest compressions are, and as soon as there is any spontaneous circulation ETCO2 spikes dramatically.

ECG is also advocated as an adjunct that can help identify rhythm disturbances which might point to a need to defibrillation in certain cases, but can only really be assessed in between rounds of chest compressions because of motion artefact. And even when you are getting accurate ECG free from motion artefact, the presence of QRST wave forms on the trace often does not indicate CPR success, given that pulse-less electrical activity is a very common finding following following cardiopulmonary arrest.

Pulse oximetry is not advocated as a useful monitoring tool during the actual CPR since motion artefact makes pulse oximetry readings inconsistent and misleading, and the length of time in between rounds of chest compressions are usually not long enough for the pulse ox to start giving accurate readings (unlike ecg), even if there was a spontaneous return of circulation.

So they suggest to hook up ETCO2 immediately once intubated, then ECG when you can, but the final and best arbiter of your CPR success will not be a machine, it will be your index finger, when you feel a femoral pulse, which confirms return of spontaneous circulation.

RE: Tanget on anaesthetic monitoring

Gwen Covey-Crump — Sat, 25 Jul 2020 11:39:25 GMT

In addition to comments below, patients in referral practice are frequently having long complex procedures and may be very sick or compromised. Furthermore, they are generally entirely covered with drapes or inaccessible for the holy grail direct monitoring (eyes, ears and fingertips). Therefore monitors become very useful when used with an understanding of their limitations, even by specialists (if you want to compare to the human care by consultants concept). I agree completely with the comments about obsessing with monitors whilst ignoring the patient - has caused me difficulties on many occasions.

RE: Tanget on anaesthetic monitoring

Clive Ansell — Sat, 25 Jul 2020 10:18:04 GMT

I don't think anyone is suggesting that we shouldn't monitor anaesthetics at all, just questioning how useful a simple pulse oximeter actually is. I'm all for a capnograph with most GA's if it's available.

I'm not sure how useful comparing human with veterinary anaesthesia is going to be, completely different entities.

I don't know whether it is still the case, but we were taught that anaesthetic deaths in our patients were 1 in 800, whereas in the human field it was 1 in 10000 ?

Many human procedures are much longer, with dire consequences if things go wrong of course.
As Mark points out they use more more relaxants and paralysing agents.
many of our procedures in first opinion work are very quick, neuters etc - it takes less time to castrate a cat than set up all the machines that go ping (or at least it should)
they have a fully trained medic, and anaesthetist at hand. We get a VN/RVN if we're lucky, if we're not we get an untrained assistant, that's it.
The problem I have seen in some low cost clinics with a very high through put of cases, is although patients are monitored throughout a GA and procedure, post op they are sometimes left unmonitored in a cage or their basket because of insufficient staff - and this is where some of the post op/ga deaths have occurred.

RE: Tanget on anaesthetic monitoring

Mark Holmes — Sat, 25 Jul 2020 09:55:26 GMT

Human anaesthesia requires muscle relaxants which requires a higher degree of monitoring but also I think it’s also a question of safety and human error. Anaesthetics can take hours which requires a level of concentration beyond which is safe.

Look at Veterinary Anaesthesia. How often are you both stood chatting away while working. Ideally everyone would be giving their job 100% focus 100% of time everytime but it’s unrealistic to expect that.

Monitors are useful in aiding where human concentration fails. I don’t believe they even need to be that accurate most of the time. They do need to catch things before you drop them. For instance the pulse ox machine - I have few problems with one reading low just as long as they don’t read high and you double check every low (ie don’t just assume it’s a dodgy reading). By understanding the limitations of your equipment you can get the most out of it without it having to be perfect.

RE: Tanget on anaesthetic monitoring

mel kavanagh — Sat, 25 Jul 2020 09:09:38 GMT

if people have general anaesthetics given by fully trained consultant anaesthetists why do they seem to need all the monitors? There must be something in it. Either they are deluding themselves or we are ? Can't both be right.

RE: Tanget on anaesthetic monitoring

Mark Holmes — Sat, 25 Jul 2020 09:05:00 GMT

I’m familiar with that exercise. I’m not sure I’ve ever had an overly optimistic pulse ox machine though. They’re usually like having a depressive friend. Useful in that good news is generally good news but don’t panic if they tell you the sky is falling in.

RE: Tanget on anaesthetic monitoring

Clive Ansell — Sat, 25 Jul 2020 08:58:35 GMT

I remember been shown, when I was a student, how capillary refill time was normal in a horse that had just died. The point was that the test in isolation is not helpful, but is just a small part of an overall assessment.

RE: Tanget on anaesthetic monitoring

Busybee — Sat, 25 Jul 2020 08:29:17 GMT

[quote userid="2675" url="~/001/veterinary-clinical/small-animal/anaesthesia/f/discussions/29247/tanget-on-anaesthetic-monitoring/224508#224508"]next time you have a pts on the table, have all the nurses to watch how long the machines start to register something has gone wrong - it can be quite a wake up call.[/quote]

This!

RE: Tanget on anaesthetic monitoring

Richard Carter — Sat, 25 Jul 2020 07:30:14 GMT

next time you have a pts on the table, have all the nurses to watch how long the machines start to register something has gone wrong - it can be quite a wake up call.

RE: Tanget on anaesthetic monitoring

Mark Holmes — Fri, 24 Jul 2020 17:38:47 GMT

I only really rate them for resuscitations. If the pulse ox can find a pulse, get a reading and it’s anywhere near 100% then the resus must be going ok. They are so shit that a decent score is a very very good sign.

RE: Tanget on anaesthetic monitoring

Clive Ansell — Fri, 24 Jul 2020 14:40:27 GMT

Most of the pulse oximeters I have come across and used seem more a nuisance than an asset. Ok when they work as an aid. I have come across too many inexperienced or trainee nurses that spend ages pratting around getting the things to work rather than looking at and monitoring the patient. I like a capnograph, but most places don't have one or don't use them for small routine ops.

There was trend a while ago to start using them in mountaineering circles on high altitude expeditions, where most of the people I've seen with them don't really understand them or what they do, or realise the limitations of them. I've seen mountaineering trips disrupted and delayed because of people becoming paranoid over readings.

RE: Tanget on anaesthetic monitoring

Kate Richardson — Fri, 24 Jul 2020 14:00:32 GMT

[quote userid="8991" url="~/001/veterinary-clinical/small-animal/anaesthesia/f/discussions/29247/tanget-on-anaesthetic-monitoring/224423#224423"]Peripheral blood pressure little correlation with central blood pressure, latter another inferential step to vital organ perfusion. Most often used under GA, where anaesthetic drugs will have an effect. Alpha 2s will give lower readings but are the only agents to maintain renal, cerebral and myocardial perfusion pressure.[/quote]

I have to say I don't notice a significant drop in peripheral BP with alpha 2's and use medetomidine in 99% of premeds in cats. Do you find it drops BP David Mills? At what doses? I use v low 0.01-0.02MLS/kg

We use a Doppler BP as I don't trust the oscillometric ones at all (not that we have one) and it's not a faff at all- we leave it on the foot/tail in place and constantly on, sometimes taped, sometimes it just sits nicely on the gel and therefore can constantly hear the pulse (and it's quite a soothing reassuring sound which I like) plus having it constantly in the background it (HR) gives me an rapid warning if the anaesthetic depth is too low when I start extractng a tooth for example as I may go from a very non stimulating part of the procedure to a highly stimulating quite quickly. I totally accept peripheral BP does not correlate necessarily with central BP but it does give you some indications if the anaesthetic is too deep, BP drops, so we can take measures to address this either by more analgesia/nerve blocks etc, so we manage to keep our iso levels as low as poss. So I don't think BP is a waste of time, and really shouldn't be a faff to do with the animal under GA, Its just becomes part of the 5 minute readings alongside hr and resp rate etc and isn't onerous at our clinic.

Echo the thought though that if a machine is being a pain, it get's turned off!!! Otherwise you waste far too much time trying to sort it out and forget the patient!

RE: Tanget on anaesthetic monitoring

Bob Russell — Fri, 24 Jul 2020 08:20:18 GMT

i find it is an irritation for dentals but you are far better at them than I am.

The monitoring nurse can access the heart for readings very easily as there are no drapes etc in the way.

Just a choice as is whether the nurse uses an amplifier or an ear piece!

RE: Tanget on anaesthetic monitoring

Evelyn Barbour-Hill — Thu, 23 Jul 2020 21:04:03 GMT

[quote userid="6550" url="~/001/veterinary-clinical/small-animal/anaesthesia/f/discussions/29247/tanget-on-anaesthetic-monitoring/224441#224441"]

We use an oesophageal stethoscope where it does not get in the way

[/quote]

I'm intrigued as to when it might get in the way! I consider the oesophageal stethoscope, with amplifier, a sine qua non. It doesn't get in the way in any dental procedure.

Our very expensive (I was an early adopter) pulse oximeter lives in the white elephant cupboard.

RE: Tanget on anaesthetic monitoring

Joyce Whitehead — Thu, 23 Jul 2020 19:47:05 GMT

I’m also of the opinion that the pulse ox is my least favourite part of the multi parameter machine, and we often take it off as it alarms at regular intervals, falls off the tongue etc. We always have nurse doing pulse and resp rate and the capnograph is so much more useful. I’m very cautious of nurses getting too caught up in messing around trying to get a machine to work when eyes and ears can be more useful.

RE: Tanget on anaesthetic monitoring

Bob Russell — Thu, 23 Jul 2020 10:07:43 GMT

Very surprised to hear much that is positive about using a pulse ox during anaesthesia. I believe it is of very limited value and is one more beeping object to distract. Perhaps some use as a patient wakes up

We use an oesophageal stethoscope where it does not get in the way but most importantly a capnograph. A lot can be read from the trace and thankfully ours stays mute unless there are issues.

Even this machine does get switched off if it is more trouble than it is worth.

RE: Tanget on anaesthetic monitoring

Evelyn Barbour-Hill — Thu, 23 Jul 2020 09:25:48 GMT

[quote userid="8991" url="~/001/veterinary-clinical/small-animal/anaesthesia/f/discussions/29247/tanget-on-anaesthetic-monitoring/224423#224423"]Add to that time pissing around getting a reading (oscillometrics are a bit like BUN strips - pick your number and cross your fingers) whilst not monitoring the vital signs of the animal...[/quote]

Well said.

RE: Tanget on anaesthetic monitoring

Rob Loxley — Thu, 23 Jul 2020 07:19:18 GMT

Put the cuff on, press auto and it pings a reading every 5 minutes?

RE: Tanget on anaesthetic monitoring

David Mills — Wed, 22 Jul 2020 22:49:16 GMT

Yeah, not sure they are well understood. SpO2 is oxygen saturation, tells you little if hypoxic or not, just how saturated the Hb is in RBCs, So it's a measure of the effectiveness of alveolar transfer of oxygen, nothing more really.

Peripheral blood pressure little correlation with central blood pressure, latter another inferential step to vital organ perfusion. Most often used under GA, where anaesthetic drugs will have an effect. Alpha 2s will give lower readings but are the only agents to maintain renal, cerebral and myocardial perfusion pressure. ACP will give normal readings (ish) but at the expense of central pressure a lot of the time. Add to that time pissing around getting a reading (oscillometrics are a bit like BUN strips - pick your number and cross your fingers) whilst not monitoring the vital signs of the animal...