Feline Premedicants

Re: Feline Premedicants

Jean-Paul Schmidt — Fri, 30 Apr 2010 22:56:09 GMT

[quote user="james hunt"]Doses I would consider using in such animals would be 1-2 micrograms/kg[/quote]

Thanks for the details James,

[quote user="james hunt"]suggestions that using ketamine in cats with HCM may have deleterious consequences,[/quote]

I have been swatting-up this evening on this subject and your cautions on ketamine use are supported by Derek Flaherty who comments that while N American vets will commonly recommend diazepam-ketamine combination for critical CV patient induction the belief that the combination will increase or maintain aBP (as seen in healthy patients) has not been demonstrated and little evidence exists to support its use over other drugs (Flaherty 2008). Dan Holden and Richard Hammond in their chapter of the BSAVA manual on Canine and Feline Emergency and Critical Care also comment that because of the pre-existing high sympathetic drive ketamine's effects on the CVS are less predictable. While they identify it as a viable choice in critical care patients they do comment that the potential increase in HR with this agent could be detrimental in HCM. (Hammond and Holden 2005). Eddie Clutton's chapter "cardiopulmonary disease" in the BSAVA manual of anaesthesia and analgesia provides more valuable information. He advocates the use of midazolam combined with ketamine and/or ACP in cats with cardiopulmonary disease but does go on to describe the needs of cats with HCM in detail and points out that cats should be suitably prepared for the anaesthetic using negative chronotropic agents such as digoxin or B-blockers and pleural disease managed appropriately. He describes the ideal anaesthetic as: suppressing HR, contractility, and ventricular arrhythmias; and maintaining filling pressures and systemic vascular resistance. (Clutton 1999). Finally, in the chapter on Echocardiography in Ettinger-Feldman's bible the author recommends retraint of feline cardiac patients with ketamine (2-5mg/kg IV or IM )+/- midazolam (0.1-0.2mg/kg IV or IM) if they are asymptomatic and if the cat is in congestive heart failure to use butorphanol (0.2mg/kg IM) and midazolam (0.1-0.2mg/kg IM) (Belanger 2005).

[quote user="james hunt"]the profound cardiovascular effects of alpha 2s[/quote]

All of the authors above criticize the use of medetomidine in critical care or cardiovascular disease patients.

Any patient with hypovolaemia should not be given medetomidine due to the profound decreases in cardiac output (Flaherty 2008). The profound respiratory and cardiovascular depressant effects produced by a2-agonists effectively preclude their use in patients with significant disease (Hammond and Holden 2005). Medetomidine should not be used for premedication in ill animals (Clutton 1999).

[quote user="james hunt"]I suppose the ease of reversal of these agents is a potential benefit.[/quote]

The availability of an antagonist does not justify the use of medetomidine or other a2-agonists in high risk cases because of the widespread disturbances they cause (Clutton 1999).

In the JSAP paper titled "Investigating medetomidine buprenorphine as preanaesthetic medication in cats" (Grint and others 2009) the combination of medetomidine with the opioid buprenorphine is shown to be safe and effective in healthy cats presenting for OOH. The main side-effects reported in the study were vomiting preoperatively and at higher doses mild bradycardia, they also commented that the pulse oximeter was likely to be unreliable and used this to explain a reduction in SpO2 in anaesthetised cats. The final point of interest, as has been your experience in dogs, was that higher doses failed to offer superior sedation and did manifest higher side-effects.

This debate has certainly changed my attitude towards ketamine, although given my own experiences I will just be more careful infuture if using this in cats with heart disease and avoid in heart failure, and it has certainly renewed my interest in medetomidine. I am still looking for data to support the CVS safety claims in low dose medetomidine but your explanations certainly make sense.

Best wishes,

J-P

References:

Belanger M-C (2005) Echocardiography. In: Textbook of Veterinary Internal Medicine. Eds S.J.Ettinger and E.C.Feldman, Elsevier, Missouri, USA. pp311-326.

Clutton R.E. (1999) Cardiopulmonary Disease. In: BSAVA Manual of Small Animal Anaesthesia and Analgesia. Eds C.Seymour and R.Gleed, BSAVA, Gloucester, England. pp161-169.

Flaherty D. (2008) Critical Anaesthesia 1. In: Vets Now, Emergency and Critical Care Congress Handbook.pp47-53.

Grint G., J.Burford, A.H.A.Dugdale (2009) Investigating medetomidinebuprenorphine
as preanaesthetic medication in cats. Journal of Small Animal Practice. pp73-81.

Hammond R. and Holden D.J. (2005) Anaesthesia and Analgesia for the Critical Patient. In: BSAVA Manual of Canine and Feline Emergency and Critical Care. Eds L.King and R.Hammond, BSAVA, Gloucester, England. pp261-264.

Re: Feline Premedicants

Evelyn Barbour-Hill — Fri, 30 Apr 2010 15:33:07 GMT

[quote user="Utlendigur"]

[quote user="Evelyn Barbour-Hill"]

[quote user="Michael Woodhouse"]There are real risks to cats from intubating them,[/quote]

What do you see as the risks? This is a genuine question, not rhetorical, but I confess I can't think of any important risks.

[/quote]

Tracheal necrosis/rupture from over-inflation of a cuff +/- long procedure. I have seen the results of this - a fairly spectacular subcut emphysema a few days post op- luckily the cat recovered ok.

[/quote]

Well, yes, but that's the result of mis-use of the tube.

Re: Feline Premedicants

james hunt — Fri, 30 Apr 2010 14:59:01 GMT

Jean-Paul

i found this abstract but unable to get full text:

http://avmajournals.avma.org/doi/abs/10.2460/javma.2002.221.1276

Re: Feline Premedicants

james hunt — Fri, 30 Apr 2010 10:05:37 GMT

I use uncuffed ET tubes in cats

Re: Feline Premedicants

Gillian Mostyn — Fri, 30 Apr 2010 10:00:03 GMT

All the problems reported with placing tubes in cats are usually caused by poor use of the equipment rather than a flawed method. Somebody mentioned that they saw laryngeal spasm in a cat when they were a student - I'd be curious to know if it was a student attempting the intubation....and being a bit traumatic....

I haven't seen tracheal damage from over-inflation of the cuff- but I was told that as long as you don't put more than a max of 2ml in the cuff that is very unlikely to happen. I have occasionally seen a nurse pick up a 5ml or 10ml syringe when inflating - but they don't do it twice!!!

Re: Feline Premedicants

james hunt — Fri, 30 Apr 2010 09:57:30 GMT

Sorry forgot to say the vasodilatory effects produced by ACP may contribute to a worsening of mitral valve prolapse (dt pressure gradient). Again good anaesthetic care such as provision of oxygen will improve O2 delivery to tissues and any reduction in CO may be compensated for to a degree.

best wishes

Re: Feline Premedicants

james hunt — Fri, 30 Apr 2010 09:48:21 GMT

Hi Jean Paul,

As I understand it, I think the increase in vascular resistance is supposed to prevent the dynamic left ventricular outflow obstrcution caused by a prolapsing mitral valve and hence reduce this dynamic 'stenosis'.

I agree with you that the profound cardiovascular effects of alpha 2s (which, in dogs, have been shown to be maximal at 5 micrograms per kilo with no increase in CV depression with increasing dose after this) could well be detrimental if not carefully monitored. I suppose the ease of reversal of these agents is a potential benefit. Doses I would consider using in such animals would be 1-2 micrograms/kg.

There have been suggestions that using ketamine in cats with HCM may have deleterious consequences, either as a result of increasing sympathetic tone and increasing heart rate still further, thus reducing ventricular filling, or due to direct negative inotropic effects in a maximally symathetically stimulated heart. I am pleased to hear that you are using the drug successfully, and think this highlights the fact that there is probably no ideal CNS depressant drug for animals suffering from a particular disease - many drugs can be used and an awareness of their properties and monitoring for these is likely to optimise outcome.

Re: Feline Premedicants

Jean-Paul Schmidt — Fri, 30 Apr 2010 08:49:54 GMT

[quote user="james hunt"]improve cardiac function by increasing peripheral vascular resistance [/quote]

I find this claim hard to understand. Surely a cat with HCM, potentially with significant tachycardia and myocardial strain as well as already increased sympathetic tone and poor cardiac output secondary to diastolic dysfunction, does not need a further increase in peripheral vascular resistance. Also, while I accept that a sensible reduction in HR may be a common part of therapy in these cases, surely a profound bradycardia could be again detrimental to cardiac output.

Finally, while this therapy may avoid a large decrease in peripheral vascular resistance surely in patients undergoing GA the concurrent fall in cardiac output secondary to induction and maintenance agents off-sets any potential for major imbalance and hence a large pressure gradient is avoided anyway without the need for routine use of medication to increase peripheral vascular tone?

I have to say my first choice for deep sedation in these cats has always been ACP, midazolam, ketamine combined injection IM; and for GA low dose ACP, buprecare premed and propofol induction isoflo maintenance. Touch wood this has not been a problem yet and although the safest combinations can be dangerous in the wrong hands, thus far I have no adverse or fatal reactions to report.

I accept that I have alot to learn about the more modern place for medetomidine in premedication of small animal patients undergoing GA, I am no anaesthetist! I am curious as to the counter arguments for my concerns and would welcome further clarification of the use and safety of medetomidine in the unstable, especially cardiac, anaesthetic patient as I currently remain sceptical.

Very interesting topic, looking forward to hearing more,

J-P

Re: Feline Premedicants

Utlendigur — Thu, 29 Apr 2010 23:10:00 GMT

[quote user="Evelyn Barbour-Hill"]

[quote user="Michael Woodhouse"]There are real risks to cats from intubating them,[/quote]

What do you see as the risks? This is a genuine question, not rhetorical, but I confess I can't think of any important risks.

[/quote]

Tracheal necrosis/rupture from over-inflation of a cuff +/- long procedure. I have seen the results of this - a fairly spectacular subcut emphysema a few days post op- luckily the cat recovered ok.

Re: Feline Premedicants

Gareth Dowdeswell — Thu, 29 Apr 2010 16:30:37 GMT

We use xylazine and ketamine in healthy young cats, some need a bit of gas, some don't. They all have an NSAID as well. It's easy to give to even very fractious cats, but they can take a long time to wake up!

In older cats we use butorphanol pre-med and then propofol induction. I'm not that satisfied with butorphanol pre-med, especially in anxious cats it seems to make them worse, to the point where IV access isn't possible. Think I might investigate some of the other suggestions here, think the 45min waiting period a lot of the combinations need might be a struggle tho!

[quote user="Evelyn Barbour-Hill"]

[quote user="Michael Woodhouse"]There are real risks to cats from intubating them,[/quote]

What do you see as the risks? This is a genuine question, not rhetorical, but I confess I can't think of any important risks.

[/quote]

The risk of laryngeal spasm is the only one I can think of. As a student I saw one cat nearly crash with laryngeal spasm despite being sprayed, but haven't ever seen another have a problem.

Re: Feline Premedicants

Hanna Bennett — Wed, 28 Apr 2010 21:36:25 GMT

[quote user="Michael Woodhouse"]

[quote user="Hanna Bennett"]don't find any dangers with intubating cats assuming they have been sprayed beforehand. What do you do with a cat that crashes if you have no iv and no tube? Scary thought....[/quote]

It seems a 'safe' combination. Young fit healthy cats seem nice and stable. Cat's that I have experience of having problems 1 had a long standing blocked bladder the other had a blocked tube - I was a student both times.

In less developed countries ketamine is used as a human anaesthetic agent alone or in combination with other drugs without access to oxygen, certainly no ET tube.

[/quote]

my first job was a very mixed practice, and we tripled all the cats (including dentals - and they never intubated these til i came along!). Worked there for two years and certainly saw more anaesthetic deaths than i have in seven years in my current job where everything (bar the really evil cats) gets a catheter and intubated. anecdotal i know, but know which i prefer! the deaths were not the old knackered dental cats, either, but the 'young, fit healthy cats'.

Re: Feline Premedicants

Evelyn Barbour-Hill — Wed, 28 Apr 2010 00:15:33 GMT

[quote user="Michael Woodhouse"]There are real risks to cats from intubating them,[/quote]

What do you see as the risks? This is a genuine question, not rhetorical, but I confess I can't think of any important risks.

Re: Feline Premedicants

Michael Woodhouse — Tue, 27 Apr 2010 22:27:13 GMT

In less developed countries ketamine is used as a human anaesthetic agent alone or in combination with other drugs without access to oxygen, certainly no ET tube.

Re: Feline Premedicants

james hunt — Mon, 26 Apr 2010 14:24:43 GMT

I'm afraid i'm unlikely to be any the wiser after i've scanned them!

Re: Feline Premedicants

Hanna Bennett — Mon, 26 Apr 2010 13:27:56 GMT

daft question but how do you know they've systolic anterior motion til after you've sedated them and scanned them

Re: Feline Premedicants

james hunt — Mon, 26 Apr 2010 10:52:34 GMT

Ha ha

aortic root!

Re: Feline Premedicants

james hunt — Mon, 26 Apr 2010 10:52:07 GMT

[quote user="robloxley"]

Are you saying medetomidine protects from arrhythmias? Not sure medetom would be my drug of choice for cardiac cases, given profound effects of alpha2s on the cardiovascular system.

[/quote]

In HCM cats with systolic anterior motion of mitral valve low doses (1-2 micrograms per kg) medetomidine have been suggested to improve cardiac function by increasing peripheral vascular resistance which ( I think) decreases pressure gradient at aortic route and stops mitral valve leaflet getting sucked into outflow track...but don't quote me on this, haven't looked at it for a while.

best wishes

Re: Feline Premedicants

james hunt — Mon, 26 Apr 2010 10:46:50 GMT

Hi,

As R loxley and others have said it's probably best to choose your premedicant drugs based on assessment of the patient and the requirements of the procedure.

I prefer IV induction over IM sedation/dissociative anaesthesia, and think having an IV catheter in place enables an appropriate speed of IV induction (ie. quite slow). Also permits administration of fluids/intraop analgesics (where I think ketamine can often be an appropriate agent).

ACP (i use 0.03-0.05mg/kg )+ opioid as described above provides adequate sedation for placid cats.

Less well handled cats will often become moderately-deeply sedated with medetomidine/opioid combinations. I generally use 10-15 micrograms per kg, others report satisfactory sedation with much lower doses (2-5 micrograms per kg).

Old/poorly cats midazolam 0.25-0.5mg/kg + opioid often produces good sedation and should have lesser cardiovascular depression.

If i dont have suitable sedation after my premedication has had an appropriate time to take effect (yes this is 45-60 mins in the case of ACP) then consider ketamine 2-3mg/kg.

Choice of opioid depending on procedure - there is some debate regarding the analgesic efficacy of butorphanol - i find it helpful for minimally painful procedures - XR etc. Buprenorphine has been shown to be an effective analgesic in many studies and due to its 4-6 hour duration is probably very appropriate to many surgical procedures. Pethidine provides effective analgesia of about an hour in my experience. If you consider the properties of the licensed opiates inappropriate I would recommend considering methadone as a useful analgesic in cats with an apparent duration of 3-4 hours.

just my 2p worth

Re: Feline Premedicants

Rob Loxley — Sun, 25 Apr 2010 18:48:21 GMT

[quote user="Matthew Scotter"]
[quote user="katie mountford"]lowdose dom in combination with an opiate[/quote]
What is the benefit? I often use this combination with cats with cardiac problems, hyperthyroid for example, as it protects from arhythmias but what is the main reason for its routeine use?[/quote]

Are you saying medetomidine protects from arrhythmias? Not sure medetom would be my drug of choice for cardiac cases, given profound effects of alpha2s on the cardiovascular system.

For routine use, why do we use any premed: analgesia, anxiolysis for increased compliance for induction/catheterisation, antiemetic (ACP).

Canvassing for opinions will just get that. There is no one recipe for premed as there are lots of different situations, temperaments of animals and ranges of experience with particular drugs.

We mainly use for cats ACP/opiod (usually buprenorphine) before propofol induction. Slightly 'scatty/nervous' cats may get ketamine also. Always given i/m (I prefer expaxial muscles with an insulin syringe/needle, rarely is scruffing needed) as much more reliable/predictable than s/c. Cats where we assess unlikely to get i/v access for induction might get medetom/opiod/ket at an 'anesthesia dose' if young/fit/routine neutering, or 'low dose medetom'/opiod premed before i/v induction. Rarely would I start off with the datasheet medetom dose; you can always give more but often need very little.

Familiarity with the drugs from both the vet and nurse point is important for safety, maybe more so than the drug itself. E.g. being able to assess what agent and dose to use in which case. Also for the nurse monitoring the GA if you mainly use ACP/opiod then change to an alpha2 drug for one case, there may be large effects on the animal's normal parameters (HR, colour, reliability of pulse ox working, BP, induction&maintenance doses needed) which can throw people.

Re: Feline Premedicants

Hanna Bennett — Sat, 24 Apr 2010 11:17:49 GMT

we premed with acp/vetergesic 45 mins before induction for routines, and give them a sniff of ketamine (0.01 - 0.2mg/kg) ten mins before induction. We find this really takes the edge off them, and getting a catheter in iv is easy as anything. Some still growl a little but they just don't care, and it adds analgesia. Also relaxes the larynx quite nicely so I find intubating them easier too - although my big tip on that is have a decent laryngoscope with a light on it - don't find any dangers with intubating cats assuming they have been sprayed beforehand. What do you do with a cat that crashes if you have no iv and no tube? Scary thought....

However, we have found that since using alfaxan they are waking up quicker, and the ketamine still seems to be hanging a bit, making them more twitchy on recovery, so alfter discussion with an anaesthetist we were recommended to go down the low dose domitor route - again reduces the CV depressant effects at that dose but will give a little sedation to allow iv access and also has a little analgesia too.

Re: Feline Premedicants

ms1083 — Sat, 24 Apr 2010 10:52:37 GMT

[quote user="katie mountford"]lowdose dom in combination with an opiate[/quote]

What is the benefit? I often use this combination with cats with cardiac problems, hyperthyroid for example, as it protects from arhythmias but what is the main reason for its routeine use? sedation?

Matthew

Re: Feline Premedicants

Jean-Paul Schmidt — Sat, 24 Apr 2010 09:01:21 GMT

[quote user="Sean Dunne"]

So what I would ask is what premeds, if any, do you folks use in practice? Am i asking too much to have a single protocol? Has anyone else had a acp/vetergesic reaction?

[/quote]

Hi Sean, my impression is that using what you are comfortable with is safest (within reason), and probably least stressfull for all concerned.

In our clinic most vets give ACP and buprenorphine combination SC/IM or IV with NSAID / antibiotic as appropriate and provided you are using 0.05mg/kg ACP this will offer reasonable sedation for handling in most cases. I think you will know at admission which cats will require a more heavy handed approach to safetly induce/handle them and for these ketamine is a good choice. IV catheters are placed in all cases either at premedication for IV therapy or at induction and cats are induced with propofol. Intubation in all cases, often with cuff-less ET tubes, and maintenance with isoflurane.

Nothing new about this but tried and tested with few if any adverse reactions.

Hope this is useful,

Re: Feline Premedicants

katie mountford — Fri, 23 Apr 2010 21:50:42 GMT

I went to a anaesthesia talk the other week where the speaker advocated lowdose dom in combination with an opiate. The dom doses are very low-end up being about 0.04ml for a 4kg cat and i use vetergesic at normal doses but they work very well-the cats are very well sedated but don't seem to have the more horrid dom effects of going blue and poor RR etc. I use vetergesic rather than torb for the better pain relief. i give it im and about 5-10mins later induce with propofol-they only need a little. The vaporiser setting is usually about 0.5-1 throughout the GA. I use this for young healthy cats, or anything that as little fractious, we tend to use low dose acp/vet for geriatrics. hope that helps

Re: Feline Premedicants

Michael Woodhouse — Fri, 23 Apr 2010 21:22:54 GMT

[quote user="Rebecca Benge"]

[quote user="Hannah Wynne Richards"]Reason for disliking IM-no control, and some go deeper than expected. [/quote]

Is this generally the reason for that people like IV induction as opposed to an IM combination?

[/quote]

How do you assess 'deeper than expected' with triple combination? I weigh and dose accurately and find them all the same. Eyes open, no blink, no response to surgical stimulation. If I inject them single handed I just give it sub cut and it works but takes an extra few minutes.

When newly graduated I used to tube cats so that I could give them extra gas and or oxygen if required [since was slower operating] but never ever found it necessary. There are real risks to cats from intubating them, I am unaware of any from Domitor (reduces peripheral perfusion and BP but my understanding was CVP normal - not that I have any means of measuring it!). Has anyone any evidence of Domitor doing harm?

I suspect rather than worrying about IV induction in cats we'd be better worrying about fluids - even if we give them sub cut. I too like buprenoprhine but can't be waiting 45mins before getting on with a cat spay - have 'proper' work to do outside

Re: Feline Premedicants

Rebecca MacMillan — Fri, 23 Apr 2010 21:03:28 GMT

[quote user="Hannah Wynne Richards"]Reason for disliking IM-no control, and some go deeper than expected. [/quote]

Is this generally the reason for that people like IV induction as opposed to an IM combination?

We do alot of domitor/ketamine IM induction with iso maintenance at our practice, and get on pretty well with it, but many of the locums we have prefer a premed of acp and vetergesic with IV propofol. I wasn't sure of the advantages and disadvantages of either method and whether I should be steering away from IM too, especially in older animals

Any thoughts would be appreciated