Felipe M.

Hi there all!

Apologies for only saying hi now! My name is Felipe Márquez Grados and I am a specialist in Veterinary Anaesthesia and Analgesia. I am based in Wear Referrals, in North East England. Although I love all aspects of anaesthesia, I do have a special interest in patient safety and the prevention of peri-anaesthetic morbidity and mortality. It’s lovely to meet you all!

I will be taking you through a condensed session on the basic aspects of anaesthesia, with an emphasis on patient safety.

Whether it’s your main area of interest or maybe not so much (which is totally fine too!), general anaesthesia or sedation are many times the first steps in the diagnostic procedures or surgical treatment of our patients, so my aim with this session is to boost your confidence in their practice, help you maximise your patients’ safety, as well as make the whole process (even!) more enjoyable too!

I really hope you enjoy this session as much as I did preparing it!

A very warm welcome to all!

Felipe

Thank you very much Victoria and Grigori for your kind words!!!

And thank you very much as well for having joined me in this course and having supported it. It means a lot!

I hope you enjoy anaesthesia as much as I do, and wish you all the very best

Kindest regards

Felipe

Replying to Mark Laloo 13/07/2022 - 10:59

Hi there Mark

Urine retention related to trazodone is a side effect that is reported in humans, but I think there is not much in veterinary patients, maybe because it does not happen as often or because it has not been reported as much. After all, trazodone has only been administered in our patients since relatively recently.

Looking at the human literature, it seems this side effect is related to the central increase of serotonin concentrations (due to the inhibition of its reuptake) together with some anticholinergic effects.

So as you well say, absolutely. This could be a factor to be taken into account, especially in animals that can potentially already show some urinary retention. However as you say, if an IDUC is in place, it is not such a big problem. On the other hand, I would say that with the evidence we have to this date, I would still use trazodone regardless (unless urinary retention MUST be avoided -cystotomies, etc..-) and only stop it if we need to rule out causes for urinary retention, should it happen.

Excellent!

Felipe

Dear Emma

That is a very sensible plan actually! You can even increase your butorphanol to 0.4mg/kg and decrease a bit your alfaxalone to 1.5mg/kg IM. Sometimes with 2mg/kg animals can go totally anaesthetised. However not having seen the dog myself, I cannot recommend one or the other better since it depends on how you perceive the dog and whether you think you have a second chance to IM inject him/her! In any case, the combination makes perfect sense and I would use it too. Oxygen therapy, although basic in any sedation, will in this case help relieve some pressure on the right heart by vasodilating the lung. The clinical relevance of this is unknown since in normal conditions the pulmonary circulation is a low resistance/low pressure system anyway, but I guess that anything that helps is worth trying!

Giving some gabapentin and trazodone orally before the appointment is a great idea. The combination is also compatible with the sedation you describe. Just make sure you gauge the effect it’s had in the animal since any sedative will have at least additive effect and potentially even synergistic effect with both drugs. If the animal comes much calmer than normal, a lower dose of alfaxalone may work nicely already. Again, your judgement will be key here.

Very interesting case indeed!

Kind regards

Felipe

Hi there Emma

I hope you are well. I had a very lovely weekend thank you! Hope you did too. Thanks for the questions, they are very interesting questions indeed!

Let’s get them answered:

1.Even though a mini-lack anaesthetic circuit is an economical choice over a T-piece in regards to fresh gas flow, it does not have the ability to perform IPPV. So if we are thinking of patient safety, the ability to perform IPPV seems crucial. So when would you choose a mini-lack over a t-piece, and vice versa?

– It is a fantastic approach indeed how you are analysing your clinical choices from a patient safety perspective. This is how I try to focus all aspects of anaesthesia at the hospital, since patient safety is the most important part of anaesthesia. As you well say, a Lack breathing system (which is a Mapleson A breathing system) is much more economical than a T piece (Mapleson D) in terms of fresh gas flow used. And this is great from a economical but also environmental point of view. However as you say, a Lack (or a mini-Lack), does not allow IPPV. This is because the reservoir is at the inspiratory flow, and as soon as we give one or two ventilations, the reservoir is filled with alveolar gas. However, it does allow to give one or two breaths, should the animal need it. So I would say in absolute terms of safety, a Lack is AS safe as a T-piece in terms of what a breathing system is. But if the animal is for example apnoeic or requires mechanical ventilation, a Lack will be impractical and a different breathing system will be necessary (i.e. a circle, or a Mapleson D -T piece, Bain).
In terms of safety on the other hand, it is best to minimise breathing system swaps during an anaesthetic to avoid introducing factors that can lead to human error (wrong connections, valves closed), so planning ahead if the animal is likely going to need IPPV definitely makes sense. However if an animal happens to need IPPV during an anaesthetic, the breathing system can be carefully changed if necessary. As a side note, consider that a Lack breathing system can behave in a more or less similar way to a Mapleson D when high fresh gas flows are used (3-4 times minute volume). This can buy us time while using a Lack to ventilate, if the animal has transient apnoea or while we are setting up a different breathing system. I would generally recommend using this feature only temporarily. Another feature to bear in mind is that (depending on the make) many Lacks have an APL valve that when closed is totally closed, whereas a modified T-piece generally has a paediatric APL valve that will open even if closed, at a certain pressure (which we call an overpressure safety feature of the valve). So, with this assumption, maybe this does put things in favour of the T-piece but not due to the breathing system itself, because of the type of APL valve equipped (which I guess depending on the make of the Lack it could be also installed in it, so it’s really just a circumstantial advantage). So to sum up, both breathing systems are equally safe, but the Lack has the impracticality of not allowing IPPV. Safety depends on other things involved, including how we plan our choices and even what the suppliers equip different breathing systems with. But having said this, provided it makes clinical sense, a Lack is a very adequate and economical breathing system ( as an example, we use it instead of circles when a circle would not be used too often in the room, to avoid having dry soda lime).

2.When using a circle circuit, is it preferable to take the circuit you’ve been using through to theatre or have a new circuit already in there? Is there a safer/better option?

– Again, excellent approach to this. I have also given this a lot of thought in the past when building routines for everyday practice. And in this case I have a clearer answer! In my opinion, it is better to have a different breathing system waiting in theatre. The reason is that this way, you will have performed your machine check and checklist for your prep area before induction, and you will have done both things as well for the theatre machine. This means that both machines are checked, safe and that this is the routine you follow -making it repeatable-. On the other hand if the normal routine is for the breathing system to be taken through from prep, that will mean that the anaesthetic machine check in theatre will never be complete, since it will be left without a breathing system waiting for the other one to come through, This also introduces a source of complications/human error, which is the connection of a breathing system to the machine while an animal is connected to it. As an example, the breathing system could be potentially connected in an incorrect manner, especially if something is happening with the patient while moving through. For this reason, I always prefer to keep key transitions where complications or errors could occur as simple as I possibly can.

3.I also wondered if I could ask you about the use (or not use) of ALfaxan in cats with HCM. All of the cardiologists that I have discussed cases with are very happy to give Alfaxan to cats if needed to perform echos (if the cat is anxious normally they would give Butorphanol 0.2mg/kg IM and then ALfaxan (2mg/kg) IM) to allow echo. In lesson three you say that you would not be happy using Alfaxan with HCM due to the possible tachycardia as a side effect, therefore should I be avoiding Alfaxan when performing echos and if so why are the cardiologists happy using it? I hope that makes sense.

– Of course! It makes sense actually. Let me elaborate a bit to explain why I may have sounded inconsistent. Animals with HCM have a diastolic failure, which results in the incomplete relaxation of the ventricles in diastole and suboptimal ventricular filling (or end diastolic volume). As heart rate increases, diastolic time decreases, exacerbating this phenomenon. For this reason, we prefer to avoid too high heart rates in these animals. As I probably said in the video, a typical occurrence in theatre is that in a severe HCM, as soon as they show nociception and the HR increases, the BP decreases, which is counter intuitive (when compared to the healthy animal). For completeness, just a reminder that we also want to avoid too low heart rates as that can also cause a drop in cardiac output when the stroke volume is limited due by a diastolic failure.
Alfaxalone does not inhibit the baroreceptor reflex and allows the heart rate to increase as a compensation to the vasodilation during induction. However some animals show a very marked tachycardia, which in the animals at hand is undesirable. However there are a couple of things to clarify. This tachycardia does not happen in every animal (actually a marked tachycardia is much less common than an unaltered or just moderate increase of the HR), and in my experience, it is much rarer when the drug is administered IM as opposed to IV. These two factors, combined with the fact that alpha-2 agonists will greatly affect the measurements of an echo and that propofol is not suitable for IM injection, make the combination you mention a very sensible option (except in cases where any of the drugs could be contraindicated for any reason) for echo cardiography.
To be fair and to complete the background, in mild HCM I would quite likely be still happy to induce with alfaxalone. In moderate and cases I would definitely favour propofol, if adequate, to try to avoid tachycardia. Should propofol not be an option for any reason, I would potentially look at a co-induction with an agent that would decrease the amount of alfaxalone required to minimise the likelihood of tachycardia.
But just to emphasise again, one vital difference as well is the effects we usually see when given IV versus those when given IM.
I hope this makes all sense!

Very interesting stuff.

Excellent!

Felipe

Hi there Mark

Great question actually.

Rapid sequence induction is actually a human term that describes the administration of a pre-calculated dose of anaesthetic plus a neuromuscular blocking agent. In human anaesthesia usually the induction agent is only used to cause loss of consciousness (when we stop communicating or counting backwards) and then a NMBA is administered to relax the larynx and intubate the trachea. In veterinary anaesthesia we are fortunately able to get away without NMBAs for intubation, but it means that we rely more on the anaesthetic agent to facilitate muscle relaxation too.

When RSI is used in veterinary context, it usually means the administration of the anaesthetic agent at a set dose in a fast fashion, so as to gain airway access fast. This is the choice sometimes in cases like: high risk of regurgitation, oesophageal or gastric obstructions, constant vomiting, hypersalivation, obesity, upper airway obstruction, among others.

The technique is used to gain rapid airway access and avoid problems like aspiration or obstruction, but is a trade-off with titration of the agent, as you say. However, when a RSI is needed, usually it is the best option for the animal in the big scheme of things. Side effects of the induction agent like apnoea and cardiovascular depression may be more apparent, but usually their importance in these animals is lower than the ongoing airway risk and therefore the latter is addressed first.

Pros: fast airway access and protection, ability to control ventilation faster.
Cons: no titration of agent, potentially more side effects from higher dose, less pleasant induction if pre-anaesthetic medication is not a possibility, complete dependency on anaesthetist as all airway reflexes are abolished fast, need for rapid airway control, need for all equipment and staff to be ready (these last two are more a requirement than a con)

So all in all, if we are a bit literal, what we do in veterinary anaesthesia is more a modified RSI (mRSI) at best as we do not give a NMBA. However the purpose and the effect is similar indeed.

In terms of drugs, propofol or alfaxalone are very adequate. Ketamine I would say is not a preferred agent if an alternative is available as the onset is slightly longer.

Co-inductions (which will also be covered in the course!) many times are overall slower in nature due to more than one agent being administered. Also we need to consider what we need the co-inductor to do for the patient and if it is then justified to introduce it as a factor. If the co-inductor is fentanyl for example, the animal could lose ability to effectively control the airway after it, hindering us taking control as the inductor has not yet been administered. If the co-inductor is midazolam, it is best given after an initial dose of inductor agent to prevent agitation and disinhibition, therefore not serving the purpose either as it will increase the induction time. Ketamine does not seem to fit the profile since its onset is longer than propofol and we will be dealing with delayed effects or having to wait, which defeats the purpose. The only one I could possibly be happy with is lidocaine, which can be given with the animal totally awake and will not cause sedation (therefore “the clock has not started ticking” for us to have to rush to gain airway control) but once the induction agent is given will blunt the cough reflex to some extent -if this is what we need-. However in the case of lidocaine, the animal needs to be stable before induction so that the time to administer the lidocaine is justified. In general terms, when considering doing a mRSI in a patient, we usually do not want to be dealing with many drugs and benefit from having a simple plan of action as we will be dealing with the airway in a very fast sequenced manner.

So in summary, yes, we will likely see more side effects from the induction as a titration is always preferable, however when we choose to implement an mRSI, it is because the benefits offset the aforementioned side effects.

I hope this helps!

Excellent!

Felipe