Felipe M.

Hi all

Great, so let’s go one by one in a summarised manner:

Noradrenaline: as mainly an alpha-1 agonist, with a bit of beta-1 (and 2) agonism too, it increases SVR and a bit of contractility and rate. So mainly a vasoconstrictor with some inotropic effects too. This is the absolute go-to for animals in sepsis as it has been shown to have better outcomes. I also use it in animals needing higher blood pressure but with a high heart rate (due to vasodilation, for example). Heart rate tends to decrease and MAP to increase when giving noradrenaline. Very predictable in its effects, however bear in mind that increasing BP by mostly vasoconstriction gives a lovely MAP with poor peripheral perfusion, and that’s why I do not use it as first instance.

Ephedrine: it works mainly through the release of endogenous noradrenaline, so it does mainly what noradrenaline does. However it is usually given as a bolus (although an infusion can be also administered). It tends to be handy for animals just needing 10-20 minutes worth of effect, having low MAP with a normal to high heart rate. Heart rate tends to decrease, MAP to increase, and sometimes depth of anaesthesia can lighten (as in itself ephedrine is a sympathomimetic). After a couple of doses, ephedrine may not work any more (it shows what we call tachyphylaxis) as its effect depends on endogenous reserves of NA. Some animals actually show tachycardia when given ephedrine, if the sympathomimetic effect overcomes the baroreceptor activation).

Dobutamine: mainly a beta-1 agonist with some b-2 agonism too. So it causes an increase in contractility and rate, with some vasodilation. It is the one of choice in animals with low contractility, or in which increasing contractility will improve cardiac performance (like mitral valve disease or geriatric animals). It tends to increase heart rate and blood pressure, however it can also cause tachycardia. In animals with several vasodilators on board (pimobendan, acepromazine, isoflurane…), it can cause a moderate to severe tachycardia with almost no improvement in MAP, due to the compounding vasodilatory effect. It can cause arrhythmia.

Dopamine: a bit of an odd one. Low to moderate doses clinically cause mostly beta agonism (up to 10mcg/kg/min), making it behave like dobutamine, and when doses go beyond 10mcg/kg/min alpha effects become more evident, causing vasoconstriction on top. It makes it handy for the average healthy animal as increasing doses if necessary will give an additional different effect to increase BP, when accurate targeting is not necessary. However it can cause tachycardia, bradycardia and arrhythmia. And as I said above, it does a bit of everything in a not-so-clear-cut manner, so not adequate when we want to target how we increase MAP (or cardiac output).

Hope this helps!

Excellent!

Felipe

Replying to Natalie Niven 28/03/2024 - 22:09

Hi there Natalie

Thanks a lot for your thoughts! Very interesting points there.

– In terms of the timing, there is no consensus to my knowledge. Obviously giving it beforehand follows the principles of preventive analgesia and maximises its effects by being in the tissues before surgical manipulation happens. However by decreasing the production of PGE2, we are taking away one of the autoregulation mechanisms of the kidney. Given that general anaesthesia can cause hypotension, I am of the opinion of having all the protection mechanisms we can. For this reason I prefer to give the NSAID in recovery, when I know the blood pressure is fine and will not drop. Alternatively, if the animal has been cardiovascularly very stable I may choose to give it towards the end of the procedure. I think the key point is to ensure renal perfusion whichever way we want to go with the NSAIDs (and in any situation, really!).

– In terms of which one to use peri-operatively, robenacoxib, meloxicam and carprofen are licensed for intraoperative use (so we can be confident they will not tamper with the coagulation to a point that will be clinically relevant). I tend to reach for meloxicam due to having more experience with it. However if the animals are on a different one I will continue with the same. Studies in general show similar enough outcomes to not have a strong preference for one or the other, so experience plays a big part.

– When it gets to chronic use, the main factor is how well the animals tolerate the drug and side effects. Both meloxicam and robenacoxib have been tested in cats with renal disease, with good results (10.1177/1098612X20935750) (10.1177/1098612X15590870). So I tend to favour one or the other for OA, depending which one gives less side effects, and always at the lowest dose that gives a benefit. Anecdotally, I seem to find some cats which will get GI side effects with meloxicam but tolerate robenacoxib very well.

– In terms of orthopaedic vs soft tissue cases, I do not treat them differently given I cannot find enough evidence to favour one or the other.

– When treating osteoarthritis, I do also find many animals respond nicely to anti-NGF antibodies. However it is important to not forget that those antibodies block pain, but do not do much for inflammation. For this reason I would still assess case by case, and always keep NSAIDs as an option even if as a pulse therapy (a week’s worth of treatment when weather is worse or the animal has done a bit too much exercise) as they will still yield the best results for OA pain, and help towards slowing the progression. Physiotherapy, either in clinic or at home, still plays an essential part of ensuring the muscle stays in shape and provides the support the joint is unable to do by itself.

Hope this helps!

Great stuff!

Felipe

Hi all

Hope you are well and had a lovely Easter!

So, my personal take is that they are very much comparable at equipotent doses. And this is a very important point. We know that dexmedetomidine is the isolated isomer that is active. Racemic mixtures have 50% of each isomer, and for this reason dexmedetomidine is twice as potent as medetomidine (which is 50% dexmedetomidine and 50% levomedetomidine -inactive-). This is why medetomidine is 1mg/mL whilst dexmedetomidine is 500mcg/mL, as the volumes given by the charts will yield equipotent dosing. Levomedetomidine has cardiovascular effects similar to dexmedetomidine, and actually reduces its sedative effects, however only at very high doses (10.2460/ajvr.2001.62.616).

In my opinion, this is pretty much where it ends for dexmedetomidine. This paper actually shows they are very similar (10.3390/ani10071240).

The only instance where I may favour dexmedetomidine is in animals where liver metabolism is not fully competent. By giving half the number of molecules per kilogram, I assume I am giving less metabolic load for the liver to deal with. However, I have serious doubts this makes any difference given the low doses commonly used, and the non-activity of levomedetomidine at normal clinical doses. Potentially in long-term infusions dexmedetomidine could be favoured as we would be giving less molecules for the liver metabolise as a constant infusion. But again, I cannot say I see a clinical difference.

Hope this helps!

Excellent!

Hi Rachel

Great question. And it seems that in general the approach is quite diverse! I will give you my take on it:

I recommend giving omeprazole the night before anaesthesia (if possible) and the morning of. Evidence says omeprazole will increase gastric pH. This will decrease the chance of oesophagtis and stricture in case of regurgitation. In the case of aspiration, the pneumonitis due to acid will hopefully be less severe. On the other hand, another point of view is that the higher pH will make the stomach content less anti-bacterial and therefore in the case of regurgitation the chances of bacterial pneumonia will be higher. Due to the fact that good airway management and profilaxis makes aspiration pneumonia unlikely, I tend to favour the use of omeprazole as many animals will have silent or overt regurgitation during general anaesthesia.

This paper here gives evidence about a dose 3-4h before anaesthesia making a difference for the pH of the stomach and the incidence of reflux.

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1748-5827.2009.00818.x

In this paper, the use of a dose the night before plus another one 3h before anaesthesia made a difference on the gastric pH and the incidence of reflux. However only one dose the day before did not have an effect.

https://onlinelibrary.wiley.com/doi/10.1111/jsap.13328

So very often I will give omeprazole IV as soon as possible, when IV access is in place. I also administer maropitant to these patients at the same time. Granted, maropitant does not have any effect on gastro-oesophaegeal reflux, but in my head trying to reduce as much as possible any nausea (from drugs and so on) is very advisable in animals with already less-than-competent lower oesophageal sphincter and tendency to regurgitate anyway.

In animals suffering from frequent regurgitation needing a routine planned procedure (like airway surgery), omeprazole is usually prescribed for several days (as part of the treatment for the regurgitation), together with cisapride, to try to reduce incidence before anaesthetising.

Hope this helps!

Excellent!

Felipe

Hi there all!

Right, as promised, here you have some examples.

– Free: patient handover sheets; pre-anaesthesia, time-out and pre-recovery patient checklists; anaesthesia machine checklists; emergency drug sheets for every patient; meetings to discuss difficult cases beforehand; debriefs after incidents or mistakes; having an open, no blame culture; ensuring everyone has proper rest; promoting a culture where people can say if they feel out of depth or not at their best; handover sheets; M&M rounds; monthly (or more frequently even!) training;

– Under 300 pounds: PVC tubes, laryngoscope, overpressure valves for circle breathing systems, airway manometers, cuff inflating devices, oxygen tubing and masks, portable oxygen cylinder, T-pieces with paediatric APL valve, ambu bag, airway box (with tubes, ambu bag, induction agent, disposable laryngoscope), bougies for difficult airways, tuohy needles for epidurals.

– Under 1000 pounds: portable pulseoximeter, portable suction unit, crash trolley/backpack, syringe driver for infusions

I am sure there are many more, but these are the ones I can think of at the moment!

Felipe