Local anaesthetic choice

RE: Local anaesthetic choice

Beats — Sat, 15 Oct 2016 23:09:00 GMT

[quote user="Rob Davis"]

[quote user="Beats"]I think there's some argument that mixing lidocaine and bupivicaine might be worst of two worlds rather than best of both[/quote]

Why?

[/quote]

The argument I've read usually goes much like this (but sometimes discusses increased toxicity and lower overall drug dose recommmendations, e.g. half-bupivicaine safe-total-dose and quarter-lidocaine safe-total-dose if mixing):

"The onset of a mixture of agents may be unpredictable as the resulting pKa of the mixture is unknown. In addition, a 50:50 mixture (i.e. lidocaine 2% and bupivicaine 0.5%) will result in half-strength concentrations of both drugs... It is possible that the lower concentration of the fast-acting drug and long-lasting drug will result in a slightly slower onset and a shorter duration than either individual agent by itself... Due to the lack of evidence showing a consistent advantage of mixing local anesthetics, a better approach is to select a single agent based on its desired predictable characterstics..." Manuel Martin-Flores, Ch4 Clinical Pharmacology and Toxicology of Local Anesthetics and Adjuncts, pp30-31, Small Animal Regional Anesthesia and Analgesia eds Luis Campoy and Matt R. Read

PS - I bought that book hoping that it would have a nice picture of technique for local for flushing ear canal - wasn't even mentioned as far as I remember - but otherwise a good read.

RE: Local anaesthetic choice

Rob Davis — Fri, 14 Oct 2016 09:11:50 GMT

[quote user="Beats"]I think there's some argument that mixing lidocaine and bupivicaine might be worst of two worlds rather than best of both[/quote]

Why?

RE: Local anaesthetic choice

Eilidh Corr — Tue, 11 Oct 2016 19:52:30 GMT

I have just started this, so cheap and easy I couldn't find an excuse not to. Lidocaine with bupivicaine in the same syringe at a rate of 0.2ml lidocaine 2% to 0.8ml bupivicaine 0.5%. Happy with longer duration of effect for maxillary blocks.

RE: Local anaesthetic choice

Beats — Tue, 11 Oct 2016 19:26:20 GMT

I use lidocaine 2% without adrenaline. Cost is about 50p a vial I think from top of my head - I use in neuters and a vial a day between neuters and dentals often suffices... then there's the syringe/needle cost...

I think there's some argument that mixing lidocaine and bupivicaine might be worst of two worlds rather than best of both. If i was doing this I'd probably try to keep to 1mg/kg each max in a dog and would wonder about use at different sites (e.g. if extracting canine could give lidoccaine infraorbital and then bupivicaine subzygomatic or something to block nerve further up at different site) - just a thought.

Benefit to me is more intra-op (for safer anesthetic in older patient) rather than post-op - so bupivicaine alone would not suit me at all.

Anyone using mepivicaine/ropivicaine?

RE: Local anaesthetic choice

Rob Davis — Tue, 11 Oct 2016 18:27:23 GMT

I guess it depends what you are trying to achieve. Lignocaine is the sensible choice for rapid onset and to provide analgesia during the procedure, but is likely to have little effect post op. Bupivicaine will give you longer post op, but takes a while (?one hour) to kick in, so not much use during the procedure.

I used to use entirely lignocaine, but more recently have moved to bupivicaine alone. On reflection I suspect this may not be the best approach, and may try mixing the two to try to get the best of both worlds.

I have heard on anecdotal report of a dog chewing it's tongue severely post op after bupivicaine administration (presumably due to numbness), though I suspect this is a rare event, and not one I've (thankfully) seen myself.

The numb mouth feeling after a visit to the dentist is not something I particularly enjoy, and I wonder if for this reason I should switch back to lignocaine alone.... Not sure there is a right answer!

RE: Local anaesthetic choice

Stephanie Wellings — Tue, 11 Oct 2016 17:36:27 GMT

Ditto lidocaine, I think the main time you want it active is during extraction so you don't have to deepen the anaesthetic too much. Because I don't expect the local to last very long, if I think it's a very painful dental I give methadone again just before discharge, and metacam at home.

I use lidocaine vials 1% and 2%, maximum total dose 4mg/kg (but usually less is required). I charge them individually (I think we charge about £15 per vial, and that includes performing the blocks) and I think that's reasonable on top of the dental price.

I have been told other people use a 50:50 mix of bupivicaine/lidocaine (with a 50% of the max dose of each being the maximum dose given) but I haven't experimented with that so can't give any feedback!

RE: Local anaesthetic choice

Evelyn Barbour-Hill — Tue, 11 Oct 2016 13:11:41 GMT

I keep this under mental review, but I'm sticking with lidocaine (=lignocaine) with adrenaline.

Quicker onset and shorter duration is exactly what I want.

These things are not expensive. Obviously they have to be paid for but the cost is so trivial it might as well just be built in to the charge for the procedure.