Felipe M.

Replying to Idris Vandekinderen 19/06/2022 - 21:43

Hi Idris

Thank you so much for the kind words! I am very happy you are enjoying the course.

That is a good point actually, let me clarify:

Both nasal prongs and nasal cannulae are methods of providing oxygen therapy to patients who need it. In anaesthesia, oxygen therapy is often administered by mask, as it is usually temporary (pre-oxygenation, recovery…). However, in some animals, longer term oxygen therapy may be needed (animals with respiratory disease, thoracic surgery, very slow recovery…). In these cases, we tend to change method on to something which is a bit easier to wear for the animal, even if moving a bit in the kennel. This is where nasal prongs and nasal cannulae play a massive role.
In my experience, nasal prongs (the clear tube with two outlets that sit on the nose and just go in less than a centimeter) are used when the oxygen dependency is only mild. Nasal prongs can achieve reasonable FiO2 (being realistic, in a dog, around 50% perhaps and of course this depends on flow administered), however they do not sit perfect in many dogs due to the design being human (which explains why the actual FiO2 is lower than in humans). Patients can also remove them easily with just sneezing, which can result in de-stabilisation of the condition. On the other hand they can be placed easily in an awake animal with minimal stress, which makes them many times desirable.
Nasal cannulae are tubes inserted inside the nasal cavity up to (I always recommend a bit less) the medial canthus of the eye. They are there secured to the animal with staples or suture. Because of this they are much more reliable as they tend to stay in place much better, so it’s much less likely to allow an animal to pull them out (although it can happen…). They can be placed unilaterally or bilaterally, and the FiO2 can be as high as 77%, depending on flow of course. This tends to be the choice for animals with moderate oxygen dependency, and usually they are placed before recovery from anaesthesia as the placement is a bit uncomfortable as is securing it to the animal. The placement and the fixation does require of a bit more experience, and as a technique it is more invasive.

Both are very valid options and play different roles in our clinical experience.

I hope this helps!

Excellent!

Felipe

Replying to Sarah Fiddy 11/06/2022 - 12:14

Hi Sarah

Thank you so much for your kind words, I am very glad you enjoyed it! Right, let’s get these interesting questions answered:

– I really like the idea of having oxygen cylinder for recovery in kennel, but if this is not possible, how long would you recommend giving oxygen post operatively? And how long should you administer oxygen via the ET tube once the anaesthetic has stopped? I try to keep the o2 going for a 2-3 minutes then switch the iso off until the animal is ready to extubate – is this ok?

I would recommend administering oxygen until the animal is clearly conscious and looking fairly recovered, for example able to move or hold their heads and responding to stimuli. If monitoring SpO2, which I would recommend in recovery, I give oxygen until the animal is consistently maintaining a SpO2 of 97% or more on room air for 3-5 consecutive minutes.
To provide oxygen, should piped oxygen not be available in kennels, the oxygen cylinder is very handy but there are other options. For example, recovering the animal in theatre using the anaesthetic machine to provide oxygen. Alternatively, if this gets too much in the way of the workflow, a splitter Schrader can be connected to the oxygen pipeline socket or to a J cylinder, which will allow us to have a second connection to oxygen. In this one we could connect a “bubbler” humidifier with a flowmeter with a “green” oxygen tube that can be used for flow by or mask oxygen therapy. Please note this latter system does not have a valve and should NEVER be connected to an ET tube.
After the isoflurane has been stopped, I usually keep them connected for a couple of minutes on just oxygen or if you have gas analysis, until the ETISO reads 0. Then I disconnect them and keep them on flow by by holding the breathing system close but not connected to the ET tube, or I take them to recovery and administer oxygen there. I do this while monitoring SpO2. If the animal is consistently saturating above 97% on room air, for 3-5 consecutive minutes, I am happy to stop the oxygen.
On the other hand, if you prefer to discontinue the isoflurane and keep them connected to just oxygen until ready to extubate, that is totally fine too! Just ensure you are very quick in spotting the cues for extubation to avoid having movement of the head while still connected and an accidental self-extubation which can cause damage.

– I try to titrate induction agents to effect slowly over a few minutes but sometimes still see apnoea – what is the best way to manage this? A nurse I once worked with blew down the ET tube which worked but I guess not recommended! In these cases I usually turn the iso off and given breathes until the animal starts to breathe by themselves.

This unfortunately happens to all of us every now and then! A strategy to prevent this, especially if alpha 2 agonists are on board or if cardiac output is low, is to have pauses of 20-30 seconds every time we reach 0.5-1mg/kg increment in the dose of propofol or alfaxalone, in order to give it time for us to see the full effect of it, which can take much longer than anticipated. Still, it can sometimes happen regardless. When we see apnoea, all we need to do is to manually support the ventilation by giving a breath every 5-10 seconds whilst keeping a close eye on the pulseoximeter to ensure the saturation does not drop (if it does, we will need to increase ventilation and ensure we are providing oxygen and that we have airway control). After a couple of minutes, the animal will begin breathing again (when the plasma concentration of the induction agent has dropped a bit). We can give some pauses to our ventilation every now and then providing SpO2 is above 97%, to give the animal a chance to start breathing spontaneously (by allowing PaCO2 to increase).
I cannot personally see a reason to blow down an ET tube and I cannot recommend it due to health and safety reasons as well as the lack of control of how much pressure and volume we are putting in the airway, therefore risking volutrauma and barotrauma. Ventilating manually using an anaesthetic breathing system is much safer for yourself and the animal, and as a plus we will be providing oxygen too, rather than room air!
I usually do not stop the inhalant anaesthetic if post-induction apnoea happens, as by manually giving breaths with oxygen and inhalant means that when the animal resumes spontaneous ventilation, the anaesthesia depth will be good due to more stable amounts of inhalant in the alveoli, rather than getting light when they start breathing by themselves until the inhalant concentration builds up. Of course this depends a lot on how deep the plane of anaesthesia is in the animal after induction. If you assess it as too deep, then waiting a bit until starting the inhalant is a sensible idea so as to not make the animal any deeper until the injectable anaesthetic has redistributed a bit.

– You mentioned briefly about not giving medetomidine to paediatric patients and I wondered the reason why and what you would prefer to use instead?

Excellent topic! We will go in more depth in subsequent sessions, but in the meantime… Paediatric patients have an immature CV system up to 3 months of age (depends a lot on each animal), which means that the contractility is somewhat fixed, and therefore the cardiac output is very heart rate dependent. By giving alpha 2 agonists we will be increasing the afterload via vasoconstriction (at the beginning), which will difficult the cardiac work. They will also cause bradycardia, which will have a direct negative effect on cardiac output in these animals. For these reasons, it is best to steer away from them until they are older than 3 months of age (again depends a lot on the animal).
Other options are an opioid only pre-anaesthetic medication, or if very young (in the first 2-3 weeks) considering adding midazolam (0.1-0.2mg/kg IM/IV). Unfortunately, midazolam sometimes has the opposite effect, causing excitation and disinhibition. When using an opioid only, methadone (0.1-0.3mg/kg IM/IV) is a good option, but alternatively, pethidine (2-4mg/kg IM administration only) usually gives a better sedation than methadone, albeit having a shorter analgesic effect.

I hope this helps!

Excellent!

Felipe

Hello all!

I would like to give you a very warm welcome to this anaesthesia course. Thanks a lot Andy for the introduction too.

I am truly excited to be doing this with you all, and really hope you have as much fun with it as I have. You may find that there might be some topics where you would have liked more information, and that is absolutely fine! This is where you can ask me any questions you may have, either to explain something I might have not made clear enough, or to expand a bit more on the subject. Additionally, anything anaesthesia is also fine even if it’s not covered in this course!

This is also a great platform for you to share cases from your practice that you would like to discuss. Associating theoretical knowledge to its application in actual cases is a great way of learning and solidifying that information.

Please keep an eye on this space as I will also post some question every now and then for you all to have a think about and discuss together.

I sincerely hope you like this journey that I have prepared for us to take together, and wholeheartedly thank you for having chosen to come with us.

Let’s begin! 🙂

Felipe

• This reply was modified 3 years, 2 months ago by Felipe M..
• This reply was modified 3 years, 2 months ago by Felipe M..