Felipe M.

Hi again Bethany

Please do send as many questions as you like, very happy to help! Medicine patients are certainly amongst the more complex needing careful balancing of the anaesthetic.
There are certainly many ways to approach anaesthesia in these animals, but I tend to focus on:
– Short acting and where possible antagonisable drugs, accounting for potentially impaired metabolism.
– Glycaemia control, as you well mentioned.
– Maintaining temperature, to not depress the metabolism of the liver, in animals more prone to hypothermia for several reasons (age, size, condition, lower liver metabolic activity).
– Maintenance of vasomotor tone, given they have higher circulating nitric oxide and are prone to hypotension, many times not very responsive to treatment.
– Accounting for a delayed drug metabolism when repeating dosing of, for example, analgesics.
– Dose adjustment if albumin is low.

So with all this in hand, I tend to use:
– Alpha-2 agonists (if over 12 weeks of age): historically dexmedetomidine is favoured as dosing is half of that of medetomidine. Theoretically, we are only loading the liver with half the metabolic burden. I do follow this thought for infusions where accumulation can happen, but for a single pre-anaesthetic sedation dose I do think pragmatically there is no clinical difference in most of the animals.
– Methadone: even if there is no pain involved in the procedure, as I can antagonise it with naloxone if necessary, to speed up the recovery. Using butorphanol is not wrong, however we lose the ability to antagonise it should we see narcosis in recovery.
– Propofol or alfaxalone: both alfaxalone and propofol are metabolised in the liver, with a small extrahepatic metabolic fraction in the lungs and kidneys. The cessation of the clinical effect happens in both cases by re-distribution rather than metabolism, so both of them are adequate.

When it gets to surgical correction, the use of PIVA for MAC sparing reasons with alpha-2 agonists or opioids is most ofter needed to help avoid hypotension, although vasoactive drugs are often needed as well.

It seems you did a great job already, and there is certainly value in following a regime we are most comfortable with!

Hope this is of help.

Felipe

Hi Laura and Scott

What an amazing and interesting topic, which is discussed a lot everywhere I find.

I honestly doubt there is any way I can give any more scientific background information than Scott has already done. What a great summary, thanks for that Scott.

I completely agree with Scott. With all that scientific background in hand, and looking at what our human anaesthetist counterparts do, paracetamol does seem to be accepted as quite safe in many scenarios, and have a fairly wide therapeutic window. This is even reflected by its wide dosing regimes that can be read on the BNF NICE guidelines. This seems to be consistent in dogs where we know acute single dose toxic levels in dogs were reached around 75 to 100mg/kg (not that I would ever recommend getting even remotely close). Cats are obviously a totally different case.

These cases where there is uncertainty about the competency of the metabolic routes and the handling of NAPQUI are certainly tricky and I would therefore stay away from it. Unfortunately we just do not have the large population data to understand better the suitability in these disease processes. All the decisions we make for our patients are risk-benefit assessments, and I would find quite hard to justify any considerable risk for the benefit achieved through paracetamol therapy, if we have other options, many of which yield superior analgesia.
I would also argue that given the lack of data, the inherent potential hepatotoxicity, and the fact that the only paracetamol preparation licensed in dogs has a literal contraindication in liver disease, should we be so unlucky to find the patient that was not fit for paracetamol, we would have a very hard time legally justifying our choice.
In general, I have to admit that although I do love paracetamol for most canine patients, I am often quite defensive in its use in hepatic disease cases. Even if I know in many cases the patient would almost certainly be fine with paracetamol, I steer away from using it if I can find another alternative. If there is no other alternative, an honest discussion with the owner with paper trail of our reasoning and written consent seems sensible.
In terms of considering dosing adjustment for these animals, and expanding on what Scott rightly said, I personally end up finding that if I am worried about accumulation (which I guess could saturate metabolic routes/deplete our beloved glutathione in impaired animals) and I am not able to predict pharmacokinetics, it’s another reason for me to just not use it. Lowering the dose obviously makes sense if accumulation is likely, but if plasma levels are too low we risk not yielding a clinical effect. So if I still were to go ahead with this, I would go with the lowest of the dosing that we know have a clinical effect but consider decreasing the doses per day to allow for a longer half life (for example to q12h or even q24h), rather than preserving a TID regime with lower dose which might not yield high enough plasma concentration, or rely on a very difficult to predict (and potentially dangerous) accumulation to do so. When pharmacokinetics start getting messy I tend to throw my toys out of the pram, but this is just my personal opinion, not necessarily the best one! In any case, monitoring, as Scott said, would be very important.

Hope this helps!

Felipe

Dear all

Hope you are well and have had a fantastic festive period.

Just wanted to thank you all for choosing Vtx and choosing me for this amazing journey through some advanced techniques in anaesthesia. It means a lot to me to have had you here for this adventure, and I am very grateful for it.

Some of the sessions of the couse have been on technical skills, however some have been an illustration of my clinical approach to different cases and in different ways. I have loved preparing every bit of this course, but in special those sessions where I have tried to translate my reasoning to you. I believe that having a scientifically sound decision-making to how we plan our cases sets foundations up on which we can very quickly build and advance our patient care. I hope you have found these sessions useful and that they maybe made you like anaesthesia even if a bit more.

Thank you once more for joining me in this adventure, and hope to meet you all again soon.

Look after yourselves.

Felipe

Replying to scott@vtx-cpd.com 31/10/2024 - 12:26

I will post below the answer to this question from the other thread in the forum. I believe they are duplicates but let me know if I am missing something!

Can I just reassure everyone that I do think about the microbiome every time I prescribe omeprazole to an animal? I do not take the microbiome lightly. And neither do I the glycocalix.

Very keen to read your take Scott!

Hello all!

Hope you are well and excited to be starting this course. My name is Felipe Marquez Grados and I am an EBVS and RCVS Recognised Specialist in Veterinary Anaesthesia and Analgesia. Together we will be going over an initial approach to the practice of anaesthesia, but also over those next steps that elevate our anaesthesia practice to the next level of confidence, comfort and safety. Whether you are starting or already have experience in anaesthesia, there should be something in that session for you! Additionally, I will be available on the forum for any questions or topics you would like to discuss. So any questions, fire away!

I hope you enjoy the session, as well as the rest of the course, and find it useful.

Welcome, and thanks for being here.

Felipe

Replying to Ursula Lanigan 23/06/2024 - 22:25

Hi Ursula

Hope you are well.

I would say in my opinion I use a similar approach to that I have in dogs, but being even more conservative and targeted with the administration of blood. Blood in cats is a much more precious resource, and therefore I only administer it when I am sure it will not be wasted through haemorrhage, unless the situation is dire and no other option is possible.
Xenotransfusion is also an option, however it is not without side effects and downsides, so if I can make it without, I try stabilising first with crystalloids/colloids if I have to, especially if by buying time means I can then give a cat whole blood transfusion (with the added benefit of clotting factors vs dog pRBC!). If xenotransfusion is the only option there is, the proportional extra volume we have available for the cat means I may be reaching earlier for it, however keeping in mind once more we are not doing something benign.
So similar approach to dogs, with the caveat of a much more scarce resource when it comes to blood. I am a bit more cautious with the overall volumes used as cats are more prone to volume overload (I try to stay below 10mL/kg, although if we have severe losses we know some of that is being lost to haemorrhage). And still, knowing that colloids are not benign and it is an imperfect way of doing things, albeit many times the only viable one. If I can get away with crystalloid resuscitation, without doubt I favour that.

Hope this helps!

Felipe

Replying to Jon H. 14/06/2024 - 09:22

Hello everyone

What an amazing topic. All the information here from everyone is absolutely golden. Thank you for having me intruding quickly to give my views on it.

Clearly synthetic colloids are falling out of favour, especially in human medicine. They have gone from contraindicated in sepsis due to risk of AKI (although the doses used in many of these studies were higher and prolonged) and recommended only for hypovolaemic resuscitation when blood products are not immediately needed, to pretty much not even for this.
The effects of colloids on the glycocalix are definitely something we need to take into account, especially when we are looking at the recovery in the more-than-just-the-anaesthetic term. Having a disrupted glycocalix will just hinder the recovery of the animals for several reasons (fluid shifts, vasculitis, etc.).

Some recent research (cannot remember the paper though) has also showed that even single doses of colloids cause an -even if- transient increase in renal function markers. Which is not great, and another reason to avoid them, together with the potential for interference with haemostasis.

However, in my view of it there is another side to this:

During anaesthesia for haemoabdomen or any other condition with an active bleeding, damage control resuscitation many times requires fluids beyond more-than-healthy doses of crystalloids, as it is not very sustainable to treat hypovolaemic hypotension with pressors (it is difficult to make up for the lack of preload with vasoconstriction/inotropy, and in some cases also quite dangerous). Where I think we see a bit of a gap between all the information we get from human anaesthesia and veterinary, is the availability and affordability of blood products.
If I had the option and the resources, it would certainly be pRBC + FFP I would be infusing from the beginning, albeit sparingly, to maintain a MAP of just about 65mmHg, accepting that a lot of it would still be lost in the abdomen before the surgeon stops the bleed. Still a good investment if it maintains perfusion, oxygen delivery and haemostasis.
However given the implications of not optimising a resource as expensive and precious as blood products or the fact that many patients only have a limited affordability, I do, if I have to, use colloids to buy myself time until the haemorrhage is controlled. As soon as this is the case, I immediately stop them and commence a pRBC and FFP transfusion. If the colloids have been wasted in the abdomen, so be it!
With all this in hand, I still know this is not the best for the glycocalix, renal function, and haemostasis. However I find many cases just cannot afford an extra FFP and pRBC to buy time, and obviously failing to maintain an MAP of at least 65mmHg would be more detrimental than giving colloids. I have to say that if the resources and finances do allow, I would rather use FFP in their instance if I can plan for it. However if the situation has rapidly changed demanding volume straight away, I may not be wanting to wait for thawing it and instead reach for colloids again (I ask for the bag, but I may only give it post-haemorrage control).

I have to say I cannot remember a case that has suffered clinical consequences of this approach, but am very conscious that it doesn’t mean it doesn’t happen. It is still not a completely benign approach. I feel sometimes it is the only approach feasible and still effective. Jon can probably testify for the fact that the first thing I ask the clinician is “where are we with transfusions?”, and with the answer I get, I manage the resources as effectively as I can for the patient.

A game-changer for me in these scenarios would be a CellSaver device, where blood could be filtered and given back as it is collected from the abdomen. However the device and consumables are also costly and need a fairly high caseload to justify.

Excellent stuff!

Felipe