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"Eye Spy"
Sedation Headaches

By Hazell Mullins | April 22nd, 2020

Hi Everyone, 

I am embarking on my first enucleation in years this morning and I am searching the internet for information and more importantly reassurance on how to perform the best nerve blocks. I have had bad experiences with eye surgery in the past and want this one to as well as a standing eye removal can go in a cow. First decision, sedation! It’s always a tricky one when it’s a surgery you don’t perform every day,  do I you want her standing, what’s the risk of her falling in the crush, how long will it last and of course how fractious is she. 

On my Instagram story the other week I posted a photo of my trusty Eoin Ryan laminated sedation chart from his publication in the Veterinary Ireland Journal. 

It’s a great support tool to have at hand especially in cases of dangerous animals where your normal dosage rates may not be sufficient. I know have it stuck on the inside of my van as I kept losing it in the organised chaos that is my van. 

My anaesthesia lecturer in university used to always compare anaesthesia to cooking – “A splash of this and a pinch of that” and she couldn’t be more right. 

Safety during surgery is paramount and I am never afraid to sedate if an animal appears even slightly dangerous. A tell-tale sign of a tough surgery ahead is when they kick fly during clipping the hair, never a promising sign. As a new grad I used to be a little wary of sedating animals for c sections in case of compromising the calf but now I put my safety and that of others first. I have had no problems using moderate sedations and calf survival and the surgery is usually a much more pleasant experience. My go to sedation for C – Sections and LDA’s is a lose dose Xylazine (0.2ml per 100kg) +/- 0.2ml per 100kg Butorphanol. They used this in Denmark when I went to see practice and it worked very well for calming the animal. I think I have delayed a few extra grey hairs appearing since I changed my attitude to using sedation. 

My second decision today is what local anaesthesia I will use, 4 point retrobulbar or go all fancy and use the Peterson block. Perhaps I should attempt the Peterson but my confidence in numbing the correct nerves is lacking. I referred to the In Practice article by Gayle Halloway and Timothy Potter and Brian Aldridge – Ocular and head surgery in cattle to learn how to perform it correctly.

https://inpractice-bmj-com.ezproxy.is.ed.ac.uk/content/inpract/34/9/518.full.pdf

It makes me think that maybe I should be attempting more nerve blocks in cows just as my equine colleagues do every day. When you go researching these surgeries you do find lots of information on techniques but it’s difficult when you’re on farm and you need to launch straight into a surgery to do this research. The ring and the line blocks get us out of trouble, but it does make me think what I can do in future to improve analgesia in my surgeries. The sedation I am going to use is my next decision and again I think about the duration, the strength, the risk of recumbency and added analgesia required. The standing Ketamine stun described by Eoin Ryan in the above paper is probably what I will choose but this could change like the wind. 

I best be off to take this cancer eye out…”see” you all later. 

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