Hello, everybody, and thanks again to Soettis for inviting me to speak tonight. So, the title I was given was, Is there such thing as perfect feline anaesthesia? And we're gonna try and answer some of those questions tonight.
So, the outline of tonight's presentation, I'm gonna talk a little bit about premedication and alternatives to the things that we would usually, go for. Again, alternatives to what we would usually go for for induction agents, analgesia focusing on the cat, pain scales that have been validated in cats. And things that sometimes people find difficult, so maintaining an airway in a cat.
And with the newly licenced Siva fluorine, I'm gonna be looking at isoflurane and Siva fluorine, comparing the two, and then a few tips on specific monitoring parameters in cats as well. So I always like to think, is there more to it than ACP and bettergesic? And is there more to it than 0.1 mL per 10 kg of dormitory and tragegezic?
And I always like to think there is, because otherwise, what is the point of all the other drugs on the shelf? And I'd try and get you guys to have a think about what you're picking up and why you're doing it. So, what I always start with when I'm thinking about a pre-anesthetic medication for a patient is I generally start with an opioid, and I pick that opioid based on how much pain I feel the animal may experience or is already in.
So, starting from drug that provides least analgesia to drug that provides the most analgesia, we have Borphenol, which, if we remember back to our opioid receptors, is a kappa receptor agonist and a new antagonist. So this traditionally will provide very good sedation, but minimal analgesia. We then have methadone, which probably provides the most analgesia out of all of them, as is a, is a full agonist at the new receptor.
We then have buprenorphine, which is a partial agonist, but remember in cats that some cats actually do better on buprenorphine than methadone. And that isn't drug related, it's individually related. So some cats, whereas traditionally, methadone, you're think in dogs, yeah, methadone, that's gonna be the best analgesia, buprenorphine.
Actually might be the better analgesia in cats. So what I tend to do, is if I think it's gonna be a painful procedure, I'd give the methadone to start with, and then swap on to buprenorphine, if that's not providing the analgesia that I need in the recovery period. And then work with the nursing team to assess the patient to decide which the patient is responding best to.
And then I add in other drugs, depending on the temperament of the patient, whether I can get an IV cannula beforehand or not. And for me, quite a lot of cats when they come into the hospital environment, are quite stressed. And I like minimal handling in cats.
And I find that if you give an IM sedation, and there's lots of other drugs that we can use that are much more cardiovascular friendly than our traditional alpha 2 agonists. Then you can obtain IV access really easily. So, talking about our opioids again, we've said methadone, but also think about what the licenced doses of the Comtan that we have.
So, in cats, the licence dose on the data sheet is 0.3 to 0.6 milligrammes per kilo.
And again, if you compare that to dogs, the licence dose on the data sheet is 0.5 to 1 milligrammes per kilo, and they're probably much higher than most people use in clinical practise. So normally for a cat, I'd probably go 0.2 to 0.3 milligrammes per kilo.
The other benefit of the methadone, other than acting on the new receptors, is that it's an NMDA receptor antagonist. And remember that that receptor is implicated in chronic pain states. So that is another very useful additive of when you're using methadone.
Buprenorphine and cats. One of my take home messages with this is, even if you administer this drug intravenously, the onset's time is still approximately 30 minutes. So that's something to think about.
If you're giving an IV pre-med, and then you're anaesthetizing the patient and then performing your surgical procedure, it's still gonna take 30 minutes for that drug to work. It's not the plasma concentrations, because it's present in the plasma, but it's the amount of time it takes to bind to the receptor. So it's very slow and it's time to bind.
And buprenorphine can provide very good analgesia in cats. The other thing that lots of studies have shown recently is that the duration of action is not necessarily as long as we think it is. And they've shown that the duration can be anything between 3 to 7 hours.
So I often see buprenorphine being written down to be given every Q8. And actually in some cats, you might be leaving it too long and they might be hitting their threshold of pain before you repeat the next dose. So just bear that in mind that actually buprenorphine in cats may be better off given Q6.
And if we can't give this drug intravenously or intramuscularly, then we do have another alternative route, and that is orotransmucosa in cats. And remember that is cats only, not dogs, and it's due to the different pH of their saliva, means that in cats, actually, that if you give it, under the tongue or into the gum, it does render it very active and it absorbs, nicely. Borphenol, I still think is an excellent drug, but it provides very negligible pain relief.
So if you need to give a drug for analgesia, then borphrenol is not the drug to choose. You need to be choosing methadone or buprenorphine. But you can use it in your patients if you want to sedate them, and you don't require analgesia.
And there are other benefits to this. It's very short acting, and you have the suppression of the cough reflex, which in some situations can be very useful. So after you've chosen your opioid, what other alternatives are there?
So traditionally, we could use meatomidine or dexametomidine, the alpha 2 agonists, Aceromazine, ketamine, and midazolam. And all of these drugs we know do have adverse effects. The alpha 2 agonists can decrease the heart rate.
They're also pro arrhythmic. They cause a vasoconstriction, and that in turn can decrease renal blood flow, which, as we're talking about feline anaesthesia, a lot of our cat population, especially geriatric cats, do suffer from chronic, kidney disease, and that's something we need to think about. That doesn't mean you can't use alpha 2 agonists in cats with chronic kidney disease.
It just means you need to be a bit careful with the dose. Aceromazine, again, all of these drugs have positive and negative effects. It's, I don't think Aceromazine in combination with an opioid is a great sedative for cats.
I think you give it to them, their third eyelid goes across, but they still look like they're awake. And then you can get a vasodilation, which can in turn if you then anaesthetize them, make the blood pressure lower than it would be if you hadn't given it. And it's long acting, so you can't reverse it.
Once it's in, you can't get rid of it. What's our next option if we need to sedate the animal? So we can use ketamine, and we can use ketamine in two ways.
We can use it at very low doses, just for its sedative effects, or we can use it in higher doses for its anaesthetic effects. But we still have to remember it's pro arrhythmic. It's renally excreted, unchanged in the cat, so it's not metabolised before they have to excrete it by the kidneys.
And traditionally, people think of ketamine as being used as, quote, cardiovascular stable. But ketamine does have direct, myocardial depressant effects, which means that if you give it to a shocked patient, you uncover these myocardial depressant effects and you can drop your cardiac output and blood pressure. It also stings IM.
And sometimes in our fractious animals, even giving a very small amount, they do not appreciate. So that is something to take into consideration. And then we can use midazolam, which we can give IM, but remember, midazolam is not licenced.
You can use it IV again, but in fairly healthy and well patients, it can cause excitation. So it's almost much better to use midazolam in combination with other drugs. Even simply, if you're thinking of a geriatric cat, you could use opioids with midazolam.
So thinking about alternatives, so they're the traditional drugs that we go for as our pre-medication, but there are other things that we can potentially use. They are off licence, so we're gonna be using these via the Cascade. Alfaxolone, there is a lot of studies reported using alfaxolone in combination with an opioid.
So either mainly be tophenol, but you could use it with methadone if you needed the analgesia from the methadone. And they've reported giving it intramuscularly at 1 to 2 milligrammes per kilo or subcutaneously at 2 to 3 milligrammes per kilo. They've had studies performed in cats with HCM.
And then they've echoed them, which shows good stability, and minimal effects on alterations in heart parameters. It can take up to 30 minutes for full effects, but normally, it probably takes 5 to 10 minutes. I, this is one of my favourite sedations in a cat, where you've gone through all your comorbidities and your patient and you think, well, I don't want to use ketamine for this reason.
I don't want to use meatomidine for this reason. You still need to sedate the patient because of their temperament. And a stressful environment that brings, bringing them into a hospital.
This I feel is a great drug, but remember we're using it off licence by the Cascade. Another alternative, of which there's been a bit of chat about lately, is oral gabapentin. Again, gabapentin is not licenced in, cats and dogs, but there are reports of people using this orally, and I've used it a few times recently and cats are not amenable to, being restrained, even for an IM or subcutaneous injection.
And the oral gabapentin, Which we traditionally, we know, we all we use as an analgesic, binds the alpha 2Delta1 subunit of voltage gated calcium channels in the spinal cord. And that's how it produces its analgesia, but it also produces some sedation with that. So we're going to take the benefit of those sedative properties and use it in these cats.
So you can use up to 20 mg per cake orally. Recently, I had a cat that was about 4.5 kgs, and we gave it 100 milligrammes.
The cat wasn't eating, but we had an esophagostomy tube in. We put it in the esophagostomy tube. And it can take up to 2 hours, but that allows us to get a blood sample from a cat, which otherwise we were unable, unable to get.
There's also reports, I know an anaesthetist who has their own cat who, gave their cat or gabapentin because the cat does not travel well and would get too stressed, and they report this works brilliantly. So again, off licence, anecdotal reports, but appears to be working very well in some cats. So our next thing is to think about what induction agent choices we could have.
So we really are limited to 3 induction agents, ketamine, propofol alfaxolone. Ah, now, it's working better. Hurrah.
So, ketamine, again, everything has got these positive and negative effects. Ketamine, dissociative anaesthesia, but this really beneficial effect of NMDA receptor antagonism, so analgesia, which has been shown, even using it as an induction agent does provide some analgesic effect. Minimal respiratory depression is always quoted, however, I do beg to differ with that, because I use ketamine in anaesthetized patients as a very effective respiratory depressant.
So, as an induction agent, maybe, but if you're giving it to a patient that's already anaesthetized, be prepared for some respiratory depression. And I find it very useful for co-induction, and what that means is giving two drugs together as an induction agent. Ketamine, you would traditionally combine with midazolam, but there are reports of combining ketamine with propofol.
And using a small amount of ketamine and then continuing the propofol to effect until you can intubate. And this is providing the analgesia from the ketamine as well, reducing your induction agent of the propofol or alfaxolone. But again, as I said before, we have these negative effects which aren't always desirable.
But remember, these are all dose dependent. So if you're using the ketamine at lower doses as a co-induction agent or as a sedative, you're gonna have much fewer of these negative effects compared to if you used it by itself as an induction agent. Onto propofol.
So, remembering that propofol doesn't have any preservative in, and it's got various things in it that bugs like to grow in. So we need to discard it fairly quickly. We've got the propofol plus formulation, which lasts for 28 days, but we need to be careful using that in cats.
The preservative in it contains a benzyl alcohol, which is fine if you're using it on one-off doses. But if you're multiply giving it to a cat, the benzoyl alcohol can accumulate, and it has been shown to be toxic. So if you're using it for a CRI and a cat, do not use the propofol plus formulation, you must use the regular propofol without preservative.
Positive effects. We always say exopathic roots of metabolism. So if an animal has any sort of liver dysfunction, then the lungs and the kidneys can metabolise some of the propofol for us.
And it's shown to be cerebroprotective. So a decrease in renal blood flow, and thus not increasing our intracranial pressure, which can be beneficial to patients with raised intracranial pressure, such as head trauma. Other drugs do also do this, so including alfaxolone and the volatile anaesthetic agents.
But again, we can have problems with propofol. We've all seen this Propofol purple, as we call, you know, most people call it. And so no matter how careful you are, and you've given it really, really slowly, there's a proportion of patients who always become a sort of nasty cyanotic colour and you have to intubate them pretty quickly.
Other adverse effects that may be in some patients, we don't want to have. So, our other option is alfaxolone. And as I said in the pre-med section, it's very useful at as a sedative sub-anesthetic doses, but remembering in the UK that is off licence.
And there are some other countries where it is licenced, but obviously for our purposes, we're in the UK. You can keep it for 24 hours, and you definitely get minimal excitation on induction. The report suggests that you get the same dose dependent effects as propofol, but reports also suggest, and there is literature to say, your heart rate is better maintained compared to Propofol, where it can drop after induction.
You have less apnea, less cyanosis, less respiratory depressant, but remember they're all. Dose dependent effects. So you need to give this drug very slowly.
The data sheet for propofol says, give propofol over about 30 to 40 seconds. Alfaxol alone says 60 seconds. So, 60 seconds when you're inducing a patient is a very long time.
So, do it with a clock. Make sure you're giving it really slowly. If you give it really slowly, you will see those better effects that have been reported.
So going on to updates and analgesia in in cats. Whenever we're thinking about providing pain relief to our patient, we need to go back to our basic sciences and think about which receptors we're blocking along the pain pathway. So we start with the, primary affluent nerve, and we have damage to tissues.
The nerve is then activated, so that's transduction. Up to the spinal cord is transmission. The signal is then modulated within the spinal cord, and then it's perceived in the brain.
And we can think of all the different receptors that act in these different locations and by providing drugs that act on those receptors, we can provide analgesia to our patients. So thinking about transduction in the periphery, what local anaesthetics that will work there, opioids, alpha 2 agonists, and non-steroidals. Thinking about transmission along the nerve, we've got sodium channels that are propagating the action potentials, and we can block those sodium channels using local anaesthetics.
We can modulate the transmission of the signal in the spinal cord by a variety of drugs, including the NMDA agonists, where those receptors are in the spinal cord, Tramadol, selective serotonin reuptake inhibitors and things like gabapentin. And then we can. And then we have to remember that.
Pain is perceived in the brain, so it's whatever that patient thinks it is. And there are descending pathways which modulate how we perceive that pain, and they include serotonin and noradrenaline, as some of their . What's the word?
Some of the molecules that act on those receptors and various things that we do to our patients and various drugs that we give them can alter the way they perceive that pain. This is quite a good way to think about how you're gonna give analgesics to your patients, but probably a lot of you can already see here, maybe there are some fundamental flaws in this Noland pea analogy for cats. And there are, because the difficulties in cats are, we can't give them paracetamol.
So, while paracetamol can be a great drug for humans and for dogs, Cats cannot metabolise it, so they're at high risk of, oxidative damage and causing hemoglobinemia. So paracetamol is not to be given to cats. Local anaesthetics, great, we can provide local analgesia to these animals, but we must be very careful that we've calculated our doses, because cats are more susceptible to the toxic effects of the local anaesthetics compared to dogs.
And if we were to start doing things like CRIs and drugs, one drug that I try and avoid in cats is lidocaine CRI. Again, because, not just because that you have to be careful with your local anaesthetic doses, but because studies have shown that you get excessive cardiovascular depression. So you get a significant drop in blood pressure when you put a cat on a lidocaine CRI as compared to a dog.
So then another mainstay of our analgesia is non-steroidals. And the question always is, what, when do I give them? In an ideal world, we'll give it prior to the anaesthesia, so thinking about preventative analgesia.
Putting the drug in before the insult and continuing it after the insult. And there are definitely studies to show that giving non-steroidals before the event is better than after. And I remember, when there was a new, meloxicam product launched that had a slightly different data sheet, you just have to be careful when new drugs come out, and it's the same drug, but a different, Company has made it because the data sheets will alter.
So I always try and read the data sheets of the drugs. And there was on one particular data sheet, there was difficulties giving IV and then switching to oral. So we tried in a few cats to give them oral on recovery.
Well, I would never do that again, and these were cat spays, by the way. They recovered the worst I've ever seen catspays recover, and after 3 cats, we said, stop. They all need to have some meloxicam in their pre-med.
So I definitely think there are studies to back that up, and from my personal experience, that is also true. But there are cases that I wouldn't give non-steroidals prior to anaesthesia. And they are, if there's a risk of hypotension during the surgery or the anaesthetic, so haemorrhage, hypovolemia, and if they have pre-existing renal disease.
Remember what our non-steroidals do. They're COX inhibitors, they reduce our normal prostaglandin production, and the prostaglandins are essential to maintain renal blood flow at times of hypotension. So what I would do in that case is you can still give the non-steroidal, but I would wait till the end of the anaesthetic when all of those risk factors have gone.
And the question I'm commonly asked is, we've done pre-J bloods and the ALP or the ALT is mildly elevated. Can I still give a non-steroidal? So it's just remembering the difference between renal enzymes and, sorry, liver enzymes and liver function tests.
Having elevated liver enzymes does not mean the liver is not functioning properly. Obviously, if they're markedly elevated or there's other clinical signs that the patient, you might want to investigate that further, but it does not preclude giving non-steroidals. And what we're trying to do with our non-steroidals is avoid this, so your inflammatory soup at the nerve ending.
And when would we definitely avoid non-steroidals? So concurrent steroids in cats and dogs is a big no because there's a huge risk of GI ulceration, vomiting and diarrhoea for the same reason, a risk of hypotension if the patient's already dehydrated. However, you don't always have to not give them.
You could just reduce the dose. So, if the patient's hyperprotemic, maybe want to reduce the dose because it's highly protein bound. If they have liver dysfunction, maybe you can still give them but at a lower dose and concurrent ACE inhibitors.
Or you might want to give it at the end of the anaesthetic. As I described before, risk of hypotension, dehydrated patient. Concurrent ACE inhibitors could render them at risk of hypotension, chronic kidney disease, and trauma, obviously, from the risk of shock.
So non-steroidals and chronic kidney disease in cats. Again, I'm commonly asked, can we give cats non-steroidals or the cat's renal enzymes, it's iris stage 2. And there is lots of evidence that has been, that is out there for us.
And what the evidence to date has shown is that there aren't any contraindications for long-term oral use in clinically stable CKDAs. And I think they're the important take-home messages from all this data that's been collected. It's long term oral use, so it's not necessarily giving IV where you're gonna have a higher peak plasma concentration, and they're clinically stable animals.
They're not, acute renal dysfunction. They're stable. But what it does show is that you want to try and give the lowest effective dose.
If the risk of acute kidney failure is low, monitoring the patient. And having stable chronic kidney disease should not be a reason for withholding analgesic therapy when it is indicated. So painful, having a painful cat and not giving it on steroidals, is not a great idea.
But, and that you can use them safely, but at judicious doses. So remember, try tapering the dose down to the lowest effective, dose that you can in that patient. And then this is the question, which happens to me all the time.
What if NSAIs are truly contraindicated? What am I left to give this cat? Which does become a problem, practically.
Because you don't want to leave the cat in pain, but then you're stuck not having very many things left in your basket to play with. So, opioids, methadone, or buprenorphine, great, tick, we can do that. What else can we do?
Well, I always think local anaesthetic. So, can I nerve block it? Or can I put some local anaesthetic somewhere?
And lidocaine plasters is a method that you can use, which I'll talk about in a minute. Both of those are fairly easy, then we could go down the routes of CRIs, bit more complicated. You need to know what the dose rates are, you need to be able to do a little bit of maths, and you then need to have a syringe driver, so equipment needs to be available.
And then as I said lastly, we could use gabapentin. Problem with this is in a patient that's potentially needing anaesthesia or surgery is it's oral only. So why should we use local anaesthesia?
So as I said, this is the mainstay of preventative analgesia. And what we need is knowledge. So we need anatomical knowledge which as vets we should all have.
There are huge benefits in all species of using local anaesthesia. And there are studies, and I, and I read one recently, which was from an intern who I worked with at Cambridge, who had done some nerve blocks on dental patients, and they showed a variety of things, including reducing the Mac that you need. And remember, the Mac is your minimum alveolar concentration.
So it's the amount of isoflurane or sevoflurane you need, avoiding additional drug requirements, and a faster time to return to eating in these dental patients. Also, other things that can help is improve recovery, reduce the hospital stay, which from the client is a reduced cost, from the patient is reduced comorbidities, decreased stress response, and they're easier to handle because they're part of their body does no longer hurt. So in cats, we said we need to be careful because of the toxicity of local anaesthetics.
So what we are going to do is some maths, and we need to calculate our toxic doses. And if we are heading towards needing too much, then what we need to do is work out our toxic dose, don't exceed that, and then dilute it with saline to make it up to the volume we need. Remember what are the clinical signs of toxicity and local anaesthetics.
They're blocking sodium channels. The first clinical signs that you see are neurological. The second are cardiovascular.
And remember, two most common local anaesthetics that we'll use is lidocaine and buppivocaine, but buppivocaine should never be administered IV. Always need to remember to aspirate back before you inject your local anaesthetic, and if you get any blood and you're using buppivocaine, you definitely need to pull your needle out, replace with a new needle, and double check that you're not getting, any blood and you're not at risk of intravenous injection. So the problem is, if we anaesthetize these patients and render them unconscious, we're not gonna see the neurological effects, which start off as twitching, and progress to confusion, becoming comatose and seizures.
We're not gonna see those, which is why we need to calculate our toxic doses. What you will see is you will see the cardiovascular effects first, which is probably then going to start scaring us all. So important to calculate the toxic dose.
And avoid exceeding it. And this little chart here will hopefully help. So on the first, the middle column here, we have lidocaine, and 2%, which is 20 milligrammes per mL.
And then next week, we have the pivocaine 0.5%, which is 5 milligramme per mL concentration of solution. And you can see the difference between the two.
Lidocaine, it's faster onset, but, shorter duration of action. So that would be very useful in things like dentals. Where you want to provide analgesia when you're removing a tooth.
And for the person doing the dental, anaesthetizing the patient, in my experience, can be quite horrific because they don't always appreciate their teeth being removed. And actually, doing a, a, a local block can make the anaesthetic so much more pleasurable, because they can't feel their tooth. The other thing, if you're gonna be using local analgesia for other regions of the body, then they, and you want it to last a lot longer, then buppivocaine might be your drug of choice.
They have different maximum doses that we can give the patient based on the toxicity effects. And at the very bottom, you can see the toxic doses. So what we do is we say, we're going to give a maximum to that patient of half the toxic dose.
So for lidocaine, the CNS toxic dose is about 12 milligrammes per kilo. So I wouldn't exceed 6 milligrammes per kilo in a cat. And for buppivocaine, the toxic dose is about 4 milligrammes per kilo, so we don't exceed 2.
Using the concentration stated here, you can see how many mLs per kilo you have. So if you had a 4 kg cat, and you were going to give it 4 milligrammes per kilo of lidocaine, that is only 0.8 of a mL.
So you can see the importance that 0.8 of a mil doesn't look like very much, but actually that's the most you want to be giving that cat in total. Also remember that you're giving local anaesthetic in other forms.
So you have in bees, and each spray contains 2 to 4 milligrammes of lidocaine. So just being careful that we don't get overexcited by the intrabe spray and excessively spray the larynx. And think that you could use the local in other forms, maybe you've already put end the cream on the cat, maybe you've put some topical local anaesthetic in its eye.
So taking into account that we're not gonna end up in a short space of time giving the patient too much local anaesthetic. Other things that we can do that are fairly simple is infiltrate local anaesthetic or splash it places. So we can infiltrate it into the skin, or we can splash it into the subcutaneous tissues while we're closing, and that can provide very good analgesia.
If you're doing something like an amputation before you transect the nerves, chopping a nerve in half will cause neuropathic pain. And applying local anaesthetic before you do that could be very useful. I've got a little photo here of something called Nikita, which we don't have in the UK at the moment, but I just put it on there out of interest because it's launched in the US.
It's a slow release formulation of pivocaine that reportedly lasts at least 4, 24 hours, which is very interesting, and maybe we need to look out and see if it eventually emerges in this country. It can be very useful for for a lot of our patients here. And if we're doing things like mammary strips in cats, that can be a fairly painful procedure.
So something very simple that you can do is deposit local anaesthetic into the tissues as you're closing it. We can also put it into spaces, we can put it into the intrapleural space, we can put it into joints, and we can put it into the abdomen. And there is evidence for putting local anaesthetic into all of these areas.
There have been some concerns over putting buppivocaine into joints that it can cause cartilage damage, but all of the studies that show that were only in vitro studies. They were not in vivo, and they were not clinically relevant. Also, people that are bipedal is always my argument.
They always put buppivocaine in your joint, and we can still walk on two legs, without having huge cartilage damage. We can also put it into the abdomen for closure, or if we've got an abdominal draining, we can put it like that. And we can put it into the thorax if we have a chest drain, remembering to do those calculations so we don't exceed the amount we're gonna give.
Putting it into a chest drain, buppivacaine can sting, that's the warning. So if I have a patient that's got a chest drain in, I will put the buppicaine in before they've recovered, so they don't notice it's gone in. Or you can give a little bit of lidocaine first, which reportedly stops the stinging and then the buppicaine.
And if we want to become a bit more advanced, and block an actual nerve, we can do that. So the two that I'm gonna talk to you about today is the maxillary nerve block and the mandibular nerve block, and I'll explain a little bit why. I tend to not do the infraorbital or the mental nerve blocks in cats because of the shape of their head.
So if we're talking about nerve blocks to the mandible, this nerve block that is demonstrated here is the mandibular nerve blocks. The mandibular nerve arrives, the picture on the right hand side where you can see the needle going on the medial aspect of the mandible, that it arrives out of that foramen, travels the law, and then comes out near the canine, as the mental nerve. In a cat, I find it extremely difficult to palpate a mental nerve, which is a tiny, tiny little hole by the canine.
So, I, if I want to do any local analgesia to the jaw, I just do the most caudal part of it, because I find in a cat, those holes on the most rostral part of the head are so tiny, I feel like I can never find them. So the mandibular nerve, where you're going to block it is located on the medial aspect of the vertical ramus of the mandible. So, the picture on the left demonstrates it in a cat.
So, if you have a cat, in lateral, you can palpate a little notch on the ventral border of the mandible. That's roughly where your needle will go. And if you look at where the eye is, you end up roughly in line with the lateral canvas of the eye.
You need to slide the needle up the medial aspect of the, mandible, draw aspirate to make sure there's no blood, and inject. To make the block more accurate, you can slide a finger, probably in a cat, you could just slide a little finger on, onto the inside of the mouth, and you can palpate that little notch on where your needle is under the, under the membranes. And then you can direct the needle closer to where you can feel the notch.
So that can be helpful. If you want to block the upper jaw, Again, there's two nerves. There's the maxillary nerve, which then becomes the infraorbital nerve.
This, again, in cats, this is my dog, by the way. Isn't she beautiful? But in a cat, I didn't have a picture of a cat, so do excuse me.
In a cat, you can see how long her nose is. In a cat, a cat has a skull, which is shaped like the picture on the left. The infraorbital foramen is almost nonexistent, and it's a couple of millimetres thick.
So I don't really fancy sticking a needle near there when the other side of the foramen is its eye or it's, globe. Because it scares me, the thought that I could, puncture it with my needle. So if I'm gonna block the, the, maxillary arcade, then I would just do a maxillary nerve block.
These are some little pictures to demonstrate what not to do. So you can see the bottom right, you can see how tiny and how thin that foramen is, which scares me a little bit. Some people also choose to block it by going up through the palette.
That also scares me because there's a, a globe there. And we need to remember to where we're directing the needle. So the picture on the dog here, you can see that you're palpating for the, zygomatic arch.
And if you go on the most crannial third of the zygomatic arch, perpendicular and stick your needle in, you will be going below the globe and directly towards the bones. There should be minimal risk of penetrating anything. Avoid redirecting your needle towards vital structures.
And then the last nerve block that I'll talk about is a retrovolver nerve block, which, again, this, this, I, learned when I went to the Natural History Museum, which is a fantastic place. And they had this great exhibition of lots of brains of animals. And what scared me was, how close the, globes are to the actual brain.
They're literally I know, you know, as a vet, we should probably know this, but actually, nobody has ever, I certainly didn't, a vet school, wasn't given a brain and some eyes. It's so close. So that scares me a little bit in cats, but we can still do it.
We just have to know what the risks are, and we just have to be careful. So you can Approach the retrolobal nerve block, dorsal media. It's the globe within the orbit.
We're going to get a needle that's curved, and we're just gonna simply slide it around the bony orbit. I would only do this if I was a nucleating a patient due to the risk of penetrating the globe, because we obviously want to, not damage it if we're keeping the eye. And remember how close that actually is to the brain.
So we're gonna aspirate. We don't want blood, we don't want CSF. If we're happy, we're going to inject.
And this is an excellent nerve block if you're removing an eye. The other thing you could do if you weren't confident doing a retroglobal nerve block is splash local anaesthetic into the socket at the end. And then I was gonna talk about lidocaine plasters, because I actually think these can be quite useful.
I find myself in situations with cats where I run out of drugs that I can give them for pain relief. So, we were talking about before, you can't give them paracetamol. We've given them opioids, but we know for multimodal analgesia, we need more than just an opioid.
We can't give them non-steroidal because the cats have got vomiting and diarrhoea, for example. So lidocaine plaster can be very useful. Again, they're not licenced, so we're using them off licence via the cascade.
What they have shown is they have done some studies where they've looked at how much lidocaine is absorbed by putting one patch on a cat. And what they have shown is that the lidocaine is absorbed into the skin, but then tends to stay there. So it's poor bioavailability and systemic uptake.
Much higher concentrations in the skin. So we're going to get local analgesia to the skin. I tend So if I was, putting it on for a midline incision, I would put the plaster, because they're quite sticky either side of the sutures, but as close to the incision site as I could.
Only because I don't, I think when I peel it off, I'm gonna peel it off with lots of sutures, and that might not be very pleasant. Some people do put it directly over the incision site. I would recommend cutting it and putting it either side.
Ben, if we're needing something else for our patient, we can think about constant rate infusions. And the most common ones that we think about are probably ketamine, and ketamine can be extremely useful. Remember we said it's got this NMDA receptor antagonistic effect.
So anti-hyperalgesia, anti-alludinic and preventative analgesic. So that is meaning it's trying to stop chronic pain developing. There's, I did a little recipe on here, to show you what, I tend to do.
The dose, the range is there, 2.5 to 10 mcg per kilo per minute. And the hardest thing I think people find hardest is, well, what concentration do I make it up to?
So, for a cat, I tend to make it up to 1 mg per mL only because you then, when you work out the amount, you get a sensible number. And for a dog, I might make it up to 2 or 4 migs per mL, depending on the size. You can also use fentanyl as a CRI.
If you find that your buprenorphine or your methadone is not providing the analgesia that you require, and you're getting peaks and troughs, fentanyl can be very useful as a CRI in cats. But we have another alternative, and we have Dexamedotomidine. And there's lots of evidence to show that the analgesia from Dexamedotomidine is very good.
But it, the side effect would be that it does to produce dose dependent sedation. But the doses we're using it for, using it as a CRI for analgesia are very, very low. So you can see there a 25 to 1/2 a microgram per kg per hour, so a really small amount for a cat.
And again, you can adjust the rate, depending on what your patient is doing. So if your patient appears overly sedated, you could reduce the amount. And there are lots and lots of positive effects, lots of research in humans using dexametdotoamine as well.
And there's just a little suggested . Concentration of how I make mine up if I was to administer it to a cat. So that's an alternative to using your ketamine and fentanyl, and obviously that's working on a different reception.
That's working on our alpha 2 receptor for analgesia. So again, another way of incorporating multimodal analgesia into into your patient's therapy. And then we need to think about how are we gonna assess them.
So, we've given our patient all these drugs, and we've written them up for all these things, but actually, we need to assess that what we're doing is working. We're not giving too much and making the patient sedated or, dysphoric. And we don't need to change what we're doing.
So, what has been validated in cats is the Glasgow pain scale. So, similar to that in dogs has now been validated in cats. And you have these pictures.
So say if you're used to using these in cats, dogs, sorry, it'll be fairly easy to use them in cats. My only comment is, for me personally, The ear picture, which is the first one I think is great, because cats in pain do do ears like that. But the second one, looking at the shape of the muzzle, I don't think necessarily depicts very for me very well personally.
But I think what needs to happen is you need to practise using them. Understand what a cat's facial expression is, and, do that in-house with with everybody that you work with, and then people will get used to using them and knowing what the muzzle expression will appear like. And then what we end up with is a score out of 20, and they suggest that 5 out of 20 is the level when you need intervention and you need to either adjust your analgesia protocol or give the cat more, because whatever you're doing is not perceived to be enough analgesia.
And this is a cat that I had in a few weeks ago, that had a really bad abdominal wall rupture. And I took the photo because I thought this cat's face depicted actually, how much pain this cat was in. And it just, the cat was obviously one of the loveliest cats, but it, .
It was sort of frozen in its tense body, and you can see the tension all across its eyes and the way its ears are flattened and the tension going up its nose into its muzzle. So I thought that was a very good picture depicting a cat in pain. So moving on from analgesia.
I know sometimes it is difficult to intubate cats, so I was going to go through intubating cats and some top tips and also some controversies that have come up over time. So, there are complications to endotracheal intubation. It's not an innocuous event.
And various things can go wrong. For a catch, probably the most important thing is that we know that their trachea can be very delicate. And what we don't want to do is stretch the tracheal wall and risk rupturing it.
And a question that I have been asked is, should you always intubate the trachea in a cat? Do you always need to do it? And there is some evidence in the literature from the SEPSAF study, which is the confidential inquiry into perioperative small animal fatalities.
And it's one of the only studies that we have in veterinary medicine where it's looking at a lot of animals and fatalities that occurred. I can't remember exactly how many cats it was, but I think it's something like 80,000 cats, were, . Included in the study.
And what this did show is that it increased the risk of death threefold by intubating cats for minor procedures. But, and this is the big but, when we read any study and we look at this one sentence by itself, we need to take it into context of what the author is trying to describe and also other things that that study showed. So that study also showed that anaesthetizing cats more than 6.
Kilos have an increased risk of death by 3 times. But does that mean we now don't anaesthetize cats that are more than 3 kg? And giving cats fluids had a 4 times increased risk of death.
So does that mean cats just don't have fluids anymore? Well, the answer is no. What it means is that we need to be careful.
And what it means is that we don't misinterpret it to say we don't intubate cats for short procedures. What it means is that we need to pay care and attention while selecting our tube, selecting the right size. We need to be careful when we move the patient, that we don't attach anything.
So I'm, everyone that I work with, we turn off all the volatile anaesthetic agent, make sure we detach, then we move the patient. There's no risk of twisting that ET tube within the trachea. And then we need to be very careful when we inflate the ET tube cuff if we do intubate with a cuff tube.
And we need to be careful during extubation as well. Excuse me. So cuff or uncuffed is the option in cats.
Now you can use either and I would not Say you have to use one or the other, think, all I would say is think about what you're doing. So if you're using an uncuffed tube, make sure you use the biggest size possible that you can get in there to stop contaminating yourself and your work colleagues. You can use different types of tubes.
So PVC tubes, the traditional, ones that are transparent. They have a, if you were to inflate the cuff, you can see that actually you can put quite a lot of volume in there before the cuff inflates very well. Compared to a silicon tube, which you only have to put a very small amount of air in before the cuff inflates.
So it's really important when you're intubating a patient to know what sort of cuff you have. So I would advocate practising in inflating your cuffs before you even put them in your patients, so you know, roughly how much, air you can put in it before you really, really expand the cuff. The other thing is that when you buy your ET tubes, you can buy cuffs of all different shapes and sizes.
And the one that is my favourite, if you look at the picture in the bottom right hand corner, you can see that there's this high volume low pressure cuff that's very square in size. When it's inflated. And what that's doing is putting even pressure over the trachea.
So that is very useful if you can find those. What I probably don't like is the red rubbery G tubes, and these are the reasons. They're opaic, so you can't see in them.
You can't see if there's dirt or anything stuck in it. They're very easy to kink. So when you bend them, you can occlude the airway.
And they have, because they're thicker rubber, they have a relatively small internal diameter. And the cuff is quite high pressure. So for a cat, this is definitely my least favourite tube.
I think if you intubate cats well and you do it using a laryngoscope, you can place a 4 to 5 cuff in most cats, and an uncuffed 4.5 to 5.5.
If you're placing any smaller tubes than that, then I would probably, and you're not using a laryngoscope, I would suggest that if you use a laryngoscope, you'd be able to get a bigger tube in and reduce contamination of the environment. If you're going to use a cuff tube, how do you inflate the cuff? So the gold standard would use a manometer, so you'd connect it to make sure the pressure in the cuff didn't exceed 12 centimetres of water.
But let's face it, that's not practical on a day to day basis. So what I would do is give a normal, gentle tidal volume breath. So, I would close the valve on the breathing system, look at the cat's chest, give a gentle squeeze on the bags.
The chest, has a normal ventilatory, normal ventilation. And only inflate the cuff until you can't hear a leak and don't inflate anymore. Squeezing the pilot balloon does not give an indication of how much pressure is on the trachea and if it feels OK.
So if you squeeze the pilot balloon, that does not tell you whether you've got a leak. What tells you whether you've got a leak is giving the patient a breath and hearing for a leak. And what are the alternatives to the endochial tubes.
So we do have something that has been made specifically for cats, and it's called the V gel. They've also been made for rabbits. And it's a supraglottic airway device.
You can, I would advise to always use it with a capnograph. There is still risk that it can twist and occlude the airway. So what this does is it does not go.
Through the glottis into the ka, it goes around the glottis and cuts it, so that then you, the patient ventilates through that device and through the glottis. What the manufacturer state is that you can ventilate them to 12 centimetres of water. So if you did need to hand ventilate the patient with a normal breath, you shouldn't get a leak with the V gels.
They've been developed specifically to the anatomy of cats and rabbits. You can put them in very, very quickly, avoid the risk of airway trauma because you're not putting anything into the trachea, which we know can be very delicate in cats. And you can re-auclave them to sterilise them.
The one thing I would say is it's really important to use it with a counter graph. You see the little pointy ends on them. That's going over the glottis, but theoretically, it can twist if you're moving the patient.
So you need to, again, be very careful when you're moving them. And if you have a catnograph, it's better because you will see straight away if you have any occlusion of the airway. And this is my big .
Advocate for using laryngoscopes. And one of the lovely nurses that I worked with said to me, a little while back, I can't intubate cats. I'm rubbish at intubating cats.
And I said, I bet you you're not rubbish at intubating cats. I bet you, you are just not using the correct laryngoscope. So, traditionally, although I work with quite a lot of left-handed people now, so you're gonna laugh when I say this, theoretically, most people in the population are right-handed.
Although I work with probably 50/50 lefties now. And the laryngoscopes that most people use are made for right-handed humans. So you turn the laryngoscope upside down compared to how we use it, which makes it perfect for intubating an animal if you're left-handed, but difficult for intubating an animal if you're right-handed, and hopefully I've got a few pictures to show you.
So this is a right-handed laryngoscope blade, so you can see the blade is on the left-hand side, the person is intubating with their right hand, and you can see that they can get the tube in really nicely next to the laryngoscope and you can see everything and it doesn't knock it out the way. My key points for intubation, if any of you are struggling, is if you're using a laryngoscope, go for a slightly longer blade, so the second size up and a shorter one. Don't touch the epiglottis, but really push on the back of the tongue and make sure that people are holding the patient properly for you.
So whenever I'm teaching a trainee to intubate, I always demonstrate by pulling the scruff up and putting my hand under their, neck. And they can really obviously see that actually putting your hand on the neck or pulling the scruff of the patient actually pulls on the soft tissues in the area and makes the view of the larynx much less favourable. So, hold the head, use, I tend to use an ear to keep the head straight, rather than the scruff or the, or underneath the neck, and that makes it much easier for the person intubating.
As compared, can you see this left-handed laryngoscope blades? The blade is at the right hand side, and the person is still right-handed, and you're trying to get the larynges, the, ET tube over the top with this blade in the way that you also can't see. So if you're struggling, swapping your laryngoscopes to the right-handed blade, if you're right-handing handed, I would suggest is a good idea.
Remember as well, you have time. So keep calm and take a breath. As long as the cat has pulses, has good mucous membrane colour, is breathing, we know actually everything's OK.
We have a breathing system, we can provide flow by oxygen. The glottis is open, the patient's breathing, they're getting oxygen into them. Ensure the patient's well positioned, so sternal recumbency is the best way to intubate patients.
Make sure they're in a straight line, the head's not kinked to one side or the other, and the head is lifted up to give you the best view. And avoid using the scruff to hold them up or pushing under the neck. It does make a difference, I promise you.
And use a laryngoscope, you will see all sorts of things that you didn't see before. Have an array of ET tube sizes. You can guesstimate most of the time, but sometimes we'll all be fooled, and actually, you need one bigger or one smaller.
So for most patients, I take 2 or 3 sizes with me. And give the inch bes time to work. It's 30 to 90 seconds.
So that is the perfect time to have a look, spray the larynx, stop. Monitor the patients, but have a brief conversation with your colleague about what's gonna happen next. That's your 30 seconds gone, and then you can try and intubate.
Don't try and rush it too quickly. And if you didn't use a larynge skate, what would you miss? The picture on the left is a laryngeal mass in a cat, so things are very, very easy to miss if you're guddling in the dark without the appropriate equipment.
Then what if we really, really can't get the endotracheal tube in, which in some situations does happen. So first in cats, I would always say twist and flick. Pushing for me never gets the ET tube in.
If you, even if the larynx looks like those two cartilages are closed, so the erytinoids are shut, you can still get the ET tube in. All you have to do is flick them out of the way. So don't push them because They won't open.
You need to use the tip of your, the slightly pointed tip of your ET tube and flick one of the retinoids out the way by twisting it, and then you'll be able to advance. You can always use a stilelet, and sometimes you can get a stilet in and then thread the the, ET tube over the top. Or if all else fails, you can use a urinary catheter.
So in our crash trolleys, we have urinary catheters with this 3.5 mL ET tube connector, which connects onto the top of your urinary catheters, and then you connect it onto a breathing system. So if you really can't get it in, at least you can provide oxygen directly into the trachea.
And if all else fails, the animal is at risk of death. Insert a needle with a syringe between the quill rings or cricothyroid ligaments. So we have this instrument in all of our crash trolleys.
And when I was a relatively new grad, I had a cat die on induction. And it ended up having some. Mass around its, pharyngeal area.
And I really wish someone would have given me these tips before that happened, because, you know, when any patient dies that we're looking after, we always feel really bad. And I felt really bad and really awful that the cat died on induction. And I didn't have these other skills that maybe I could have been a bit braver.
Maybe we could have had a, maybe there would have been laryngoscopes ready, maybe there would have been a urinary catheter ready. Maybe I could have, poked it with a needle and syringe between the cricothyroid ligaments. All of those may have saved the cat.
So take, take these tips home with you. And then we're gonna maintain anaesthesia. So our two options are isofluorine and sevoflurane.
And as I said before, sevofluorans are now licencing cats, which is great news. Like any, like all the other drugs that we've talked about up until now, isoflurane and sevoflurane both have their pros and cons, and both require different, different amounts. So using this little graph here, we can depict what would happen if we were doing a spay of an animal.
The amount of surgical stimulus we think the patient might have. And if we were to just set our vaporizer at 2% and just leave it there and not alter it, depending on the depth of the patient, effectively we end up for most of the anaesthetic overdosing the patient. And then we would have all the negative adverse effects, a drop in blood pressure, drop in heart rate, drop in respiratory rate, which is why we need to alter our vaporizer in line with the depth of anaesthesia.
But if there's too much of a lag effect, and the patient can become too light, as the anaesthetic takes time to be breathed in across the alveoli and go into the blood. So what we want is this ideal plane of anaesthesia, which is, in practise, very difficult to achieve, but slightly more achievable with Siva flurane because of its fast onset, offset time. So, Siva fluorine is very, insoluble in the blood.
So it takes a very short amount of time for it to reach equilibrium. So it's fast onset, so they become To a more stable plane of anaesthesia, quickly, when you alter your vaporizer, they alter your depth much more quickly and in recovery as well, you have less dissolved in the blood, there is less to be breathed out before the patient recovers. But what you can see here, it's the same as a dose with any drug.
The Mac is the minimum alveola concentration, and what this suggests is you need approximately 2.6% sevoflurane to keep 50% of patients not moving, compared to isoflurane, which is 1.6%.
So what that shows is that it is normal if you're using sevoflurane and not used to using it, that you might need a slightly higher vaporizer setting than isoflurane, and that is normal, just as as opioids all have different doses amongst them, so do the volatile anaesthetic agents. But that can be beneficial for us, because what that gives us is this big range receiver fluorine. So actually, you can titrate the drug better to effect.
So, because it's got a very fast onset offset, you can t sorry, I can't talk, titrate it down and, hopefully minimise all that cardiovascular depression that you do get with ace flurane. For surgery in our patients, what you do, what it is shown is that the Mac is generally not enough to keep the patient anaesthetized, and you may need up to 1.5 times your Mac.
But there's lots of other things that alter the amount, the amount of volatile anaesthetic, that you will need. Main ones are age, so geriatric patients or young patients, and if they have any underlying disease, but also all the other drugs that we give them beforehand. So if we've given them drugs in their pre-med that cause sedation, if we've given them analgesia, that will actually alter the amount that you need to give, and you will need to give less.
They all cause dose dependent respiratory depression. So you'll get a reduced tidal volume and a reduced respiratory rate in some situations. And how, how would we monitor this respiratory depression in our anaesthetized patients?
The best way to monitor it is using a catnograph, so looking at your endide or carbon dioxide concentration, that's the amount of carbon dioxide the patient's breathing out. Using your SPO2 on your pulse oximeter is a very, very late indicator of respiratory depression and it's not that useful to suggest that the patient is breathing well or not. So if you don't have a cat graph, you will be more reliant on just looking at your patient's respiratory rate.
What Sivaflurane is good at though, is that there is less respiratory depression than with isoflurane at comparable concentrations. And again, we always say that volatile anaesthetic agents causes cardiovascular depression. But what do we mean by that?
Well, they can drop the heart rate, they can drop the blood pressure, and they can, in some situations, drop the contractility of the heart. Isoflurane and sevofluorine tend to drop the cardiac output by vasodilating the patient. But again, how do we monitor this cardiac output?
In practise, we can't. So you have to use the next best thing, which is blood pressure. So if you have a Doppler and you're not using it for your anaesthetic, get it out and use it.
And the important thing is cats is the Doppler is giving us somewhere between mean and systolic. So the minimum value we want to accept as normal in a cat is more than 80 millimetres of mercury. And then our other parameters that we can look at are heart rate, pulse quality, mucous membrane colour and capillary refill.
So as we said, they both provide comparable cardiovascular profiles, but because you can titrate the sea of fluorrane more accurately to effect, you potentially need less and therefore your blood pressure is better maintained. And then just at the end, if you're all still with me for one more minute, just a few monitoring, specifics in CATS. So, I mean, remember why we're monitoring the patient.
We're try we've rendered the patient from being normal and having homeostatically normal cardiovascular respiratory system to a level of unconsciousness that also impacts on all of those body systems. And we're trying to maintain them whilst unconscious and having whatever procedure performed as close to as physically logically normal as possible. So we're maintaining the depth of anaesthesia.
We're ensuring the safety of the patient, the safety of the personnel around, but also monitoring the patient is a legal implication. So it's not just writing numbers on a form. Obviously, the form is a legal document, so it should be filled in as accurately as possible.
But monitoring is a constant process, and the recording where you write something down is intermittent. Specifics in cats. So all patients that are anaesthetized will experience what I call a three Hs, so hypothermia, hypotension, and hypoventilation.
But specifically in cats, using an osciometric blood pressure, so the automated ones. Unless it's something like a cardell, which, sadly, we cannot buy anymore, do not work very well because the cat's limbs are so tiny, the machine can't feel the pulse, because most of them are designed for humans. So, I find the best monitoring for me and a cat is a Doppler.
Not only can you actually hear the pulse, so number one, tick, I can hear my patients alive. 2, we can get a blood pressure very accurately and it's been validated. Important point is if you're using a Doppler on a dog, it's gonna give you systolic pressure.
But on a cat, it gives you a reading of somewhere between systolic and mean. So you're aiming to maintain the Doppler above 80 millimetres of mercury in a cat as normal. Also, I find that when I anaesthetize cats, if their heart rate drops below probably about 100, it seems to have a knock-on effect and drop their blood pressure.
So, if I see a cat with a low heart rate, immediately, I will check the blood pressure. And if the blood pressure is low, you generally need to do something to increase the heart rate to increase the blood pressure, because it's the heart rate that is counteracting the cardiac output in this situation. If you have done everything, so maybe you might want to antagonise your Metaomidine, if you've given quite a lot of meatomidine, or you need some surgical stimulation, or you've checked your depth of anaesthetic, you're not too deep, you don't need to drop your isoflurane or see the flurane, then my drug of choice would be glycopyrolate, which is very similar to atropine.
So if you don't have glycopyrelate, you could use atropine. And that will increase the heart rate into a normal value and then you will often find that your blood pressure then becomes normal. Cats get very cold.
So I'm a big fan of bubble wrap. I think bubble wrap fixes most cold things well. If you, if you put it on before they get cold.
If you've got baby socks, you can wrap them up in baby socks. And then warm fluid, there is only any point in warming the fluid directly as it enters the veins. There's no point in warming up the bag of fluid, because by the time it's hung up and it goes down the giving set, it'll be cold.
So you can wrap something around the fluid line just before it enters the vein, and that can help. And that's it for tonight. Thank you all for being very patient.
I'm a bit, a little bit over time. Thank you for being patient with the slow laptop, and thanks again to Zoettas for inviting me to speak. Wow.
Thank you, Joanne, so much, for that webinar. I'm sure everyone found it really useful. I certainly did.
We've had a lot of questions submitted. But just before we go to the questions, the webinar vet team really appreciate your feedback. So if you could spare just a few seconds to complete the feedback survey, that should have popped up in a new tab in your browser, that would be absolutely fantastic.
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The webinar recording and the CPD certificates will be available online, usually on the website within 48 hours. So it's question time, and, as I said, there have been a lot of questions submitted, and Joanne has kindly said that any questions that we don't manage to discuss on the webinar, if you email the questions to office at the webinar vet.com.
The team will forward those questions on to Joan. So, One of the first questions that was submitted, Joanne was, what's the dose used for buprenorphine for sedation slash analgesia? OK.
The dose is 0.02 to 0.04 milligrammes per kilo.
So what there has been is, most people would probably use 0.02 makes per kg. And we've always been taught that you get this, bell shaped dose response curve where if you start giving a bigger dose, you end up with less analgesia.
But what they've show, what some people have shown and suggested that the doses we're using clinically, which is 0.02 to 0.04 megs per kg, you don't reach the other side of the dose response curve.
So you could, if you're using 0.02mg per kg and you find you need more analgesia, you could theoretically increase the dose and see what happens. OK.
Thanks for clarifying that. And the next question, how can we be assured that the cat won't swallow the oral trans mucosal buprenorphine? And if the cat does swallow it, does it still have an effect?
Yeah. No, you can't be sure, unfortunately, you have to try and put it under the tongue. And, or into the gum.
So, obviously, the difficulty is you're often doing it because of the cat's temperament, unless it's the owner doing it at home, obviously, and you've sent them home with it. You just, you need to try as much as you can and then assess the response of the patient. Remembering that if, if the cat swallows it, it's not gonna work because it's just not absorbed from in the solution that it is.
Orally effect orally. So it's not gonna work if it swallows it. I'm sorry, the answer is you're probably not gonna know, you're gonna have just have to do your best and then assess the response of the cat.
Thanks, Joan. And the next question, the use of midazolam and some other benzodiazepines is mentioned to cause hepatic necrosis. Have you seen this with your patients?
No, I think, I thought it was diazepam that did that, and I thought it was more in reported in dogs, I think. I've never seen it, no. And I probably use a fair amount of midazolam, but it's it, remember, it is off licence, so you're having to use it via the cascade.
I personally have never seen it cause hepatic necrosis. I don't use diazepam. I, I'm not sure.
I'd have to check the literature. I thought it was diazepam that had been reported to do that. I could be wrong.
OK, thanks. And the next question, please, could I ask your opinion on the use of fentanyl patches and cats? OK.
. I don't know if I, OK. Sorry. I'm gonna try and get my answer together.
My opinion, probably my opinion is, I don't ever use them now, but that's because I primarily work out of a hospital. I so you could They could work. You just have, there's a lot of reasons why you just need to be careful with fentanyl patches.
The potential for abuse, the potential for other animals to become exposed to them, the potential for children to become exposed to them. The fact that if you're sending, I presume they're using them because they're sending their patient home with them? Rather than in a hospital.
I think if it's in the hospital situation, I think we've got better drugs that are licenced in other animals. So fentanyl as fentedon is licenced in dogs, you could use that via the cascade, whereas the fentanyl patches aren't licenced at all. So, for me, if it was in in a hospital situation, I would never use a fentanyl patch, because I think you can be assured you're getting the analgesia into the patient by other methods.
If it was an at home situation, then I think at home analgesia is difficult, and I think I would try it and see how the owner. So, I think at home analgesia for chronic pain. Is always based on quality of life studies, doing quality of life questionnaires with the owners, seeing how the owner finds the patient responds, but also making sure all the safety things have been gone through with the owner.
So, you know, what happens if a cat goes and sits on the radiator or on the hot water bottle and it starts absorbing lots of fentanyl. That probably hasn't answered the question, so I'm really sorry. There's lots of things to think about, isn't there.
But obviously, if you, if you run out of options, which we know in catch, you do run out of options, and you definitely run out of options at home, then it's worth a try, I would say. But again, it's about discussing it with the owner and seeing how they feel the patient responds. OK.
The next question, would it be acceptable to give a CRI of ketamine, or would that have an effect on the blood pressure as well? Thank you. No.
You can give a CRI of ketamine to pretty much all patients. Sometimes people are worried about giving CRIs of ketamine if the patient has renal disease because it's renally excreted. The only thing, it's not gonna damage the kidneys.
Unlike something like non-steroidals actually may damage the blood flow to the kidneys. All it's gonna do is maintain in the body for a bit longer, so you just might need to use a slightly lower dose. CRI of ketamine at the doses that I've given there does not affect the blood pressure.
OK, so yes, it's a very good analgesic. And you can use it on top of stuff. So even if you've done a nerve block, if you have a patient, so definitely things that you think are chronic pain, you can put a CRI of ketamine on in the hope that if you put it on for 24 hours or so, maybe you can modulate all of that chronic pain component in the dorsalha of the spinal cord, and have some effect there.
So, yes, you can combine multiple things. Very, at those rates, minimal effect on blood pressure, and respiratory pretty much doesn't do anything. If the patient was conscious, I tend to give them 2.5 to 5 mcg per kilo per minute, only because of the higher rates of 10, it can make them dysphoric.
So I reserve the 10 for when they're anaesthetized and then give them lower rates when they're conscious. And we've got another CRI question. Can you use methadone in a CRI either as a sole agent or with ketamine, or is fentanyl better even when respiratory respiratory depression is an issue?
OK. So, two-fold question. One is, methadone is not suitable to be used as a CRI because it's volume of distribution is giant.
So, I vaguely remember pharmacokinetics and pharmacodynamics, which I'm sure everybody remembers way better than me. But yeah, the volume of distribution is so big that you need to give such a big dose to fill up the central compartment that it does not render it suitable as a CRI. So your drug of choice, if you need an opioid as a CRI would be morphine or fentanyl.
Fentanyl is obviously licenced in dogs, so it's slightly closer to following the cascade than using morphine, which would be off licence. And respiratory depression and opioids. My take home message on that would be every drug causes adverse effects, but it all depends on the physiological state of the patient that you give it to.
So if all the analgesic drugs, so if you take a dog that is healthy, has nothing wrong with it, and you give it methadone pre-med, it starts panting and drooling everywhere. If you give a very painful Do the same amount, it probably says, thank you very much. Now I'm gonna lie down and have a nap.
So it all depends on the physiological state of the patient. So at the dose rates, the fentanyl CRI that are in there, you are very unlikely to get respiratory depression. You're more likely to get it if you've combined it with other drugs when they're anaesthetized.
In a, if you're using it in a conscious patient, it is very unlikely to cause respiratory depression. Great, thank you very much, Joanne. Are you OK for some more questions?
Yeah, go for it. Local anaesthetics, do you ever mix lidocaine and buppica? No, I don't.
And the reason is, so theoretically. If you mix the two together, you would hope to get the fast onset from the lidocaine and the long duration from the bivvicaine. But when studies have been performed doing that, it doesn't actually do what you think it does, and I think that's to do with the.
PH and the PKAs of the drugs, which, when you combine them, alters the formulation effectively, and then you get different ionised and ionised fractions, so you don't actually get what you think you do. So actually, it's better just to use one or the other. OK.
Thank you for clarifying that. The next person says, I've heard that Dex melaomidine is synergistic with butorphenol, and this combination is a really good analgesic. Have you got any comments on that?
So the word synergistic would probably be my first comment, but all of the drugs listed in the presentation are synergistic in terms of that you combine them and you get more of effect than if you had one individually by itself. But I wouldn't still wouldn't use butterphennil as an analgesic. There are some people who would argue, not very many people, maybe a couple, who would argue that butorphnil is an excellent analgesic in cats.
And several years ago, or maybe quite a lot of years ago, there was, there is one, there's probably one study that I can remember out there where they gave butorphennil to these cats that were in a colony, where they're like, something like 8 cats in a colony. And they showed that I think they did thermal threshold testing, and that if they gave them butphenol, their thermal thresholds increased. Now, when they actually transfer that into a clinical situation, butorphennol does not provide appropriate analgesia for a cat.
So, If you're gonna combine them, yes, you can combine any of the drugs, pretty much, remembering that if you're combining lots of them, maybe you want to use a lower dose. But buorphenol, for me, is not an appropriate analgesic for a cat or a dog. And if you want analgesia, you should be using methadone or buprenorphine.
OK, thank you, Joan. Do you cut down ET tubes, to size to minimise dead space? Yes, I do.
So just remembering that, so what we're talking about dead space is anything that makes the trachea longer before you get to the breathing system. So if you're, say you're using a T piece or a mini lac on a cat, if you've got a very long, like the 5s always come in like this giant length that you think, that's the whole length of the cat. So yes, take the ET tube connector off, shop it to length, stick the ET tube connector back on.
Otherwise you'll end up with dead space. If you're using a capnograph, you'll be able to see that the patient is rebreathing CO2. Because what happens is that ET tube is too long, the patient hasn't got a big enough tidal volume, you've effectively doubled the length of the trachea, and then the carbon dioxide hasn't got to where your breathing system connects.
The patient starts to breathe back in and there's still carbon dioxide in that tube. So it's re-breathing carbon dioxide, which is not good. So, yes, cut them to length.
Great. Do you have any thoughts on the quads in kittens? If it's so great, why don't we use it routinely on all cats?
Why save it just for kittens? I know. So, in all honesty, I never use the quad.
And I think the quad has been developed for, Neutering clinics where you've got high volume. It's relatively safe, if that is a good word for anaesthesia in terms of the drugs that's in the combination. From the fact that you're hoping to maintain, you're not using something like propofol, which we know can cause cyanosis, whereas ketamine doesn't.
Yeah, that's a really good question. I, for me personally, and some of these are personal things, I don't like ketamine. When cats are anaesthetized purely with, not purely with ketamine, but ketamine in a combination, a decent dose to anaesthetize them, I don't like their recoveries.
And that's what stops me. And, you know, they salivate loads. They end up with just all this drool in their mouth.
And that's what I don't like about it, which is why I prefer to use propofol or alfaxolone, but it all depends on the environment you're working in. If you've got a really high throughput. And you're doing it in a neutering clinic for charity, that I think is more what that protocol has been developed for.
Great, thank you. I think we'll make this the last question, and I'm sorry, there's been so many questions that have been submitted that we're not gonna have time for. But somebody said, you didn't mention anything about extubating.
Have you got any advice for this? So I, I I get the point is maybe that we've been taught to extirpate earlier in cats. So yes, I do think cats are more prone to laryngeal spasm.
I would. You I still wait until the cat. I don't necessarily take it out before the cat coughs, but if the cat coughs, I quickly take it out.
Whereas a dog, you can often leave it until they're sitting up looking at you. I guess that's the difference. Make sure the cuff is well deflated.
I keep it in until I'm happy the cat is. Becoming light enough that I can then remove it. I make sure it's all untied, so if they have a sudden recovery, then I can remove it very quickly.
And yes, I would just remove it a little bit earlier than a dog. Because they are, they do just have a slightly more sensitive larynx. Well, Joanna, thank you so much.
This has been such a brilliant webinar and all the questions have been submitted, but also lots of people singing your praise as well. People have really enjoyed it. So I would really like to echo everyone's, praise that's been flooding in.
And thank you very much again to Zoetis for sponsoring this fabulous webinar provided by Joanne. Thank you to everyone who provided, who, sorry, who attended the live webinar. It's always great to see so many of you online and for providing feedback.
And as I said, any outstanding questions that you'd really like, to put to Joanne, if you email the office office at the webinar vet.com, and we can get those to Joanne. And, last but not least, thank you very much to Katherine and Rich for co-hosting with me on this webinar.
I really hope you enjoy the rest of your day, and I hope that you can join us on another webinar soon. Thanks very much again, Joanne, and, we'll speak to you again soon.