Wednesday, October 19, 2011

698. Pterygia and glaucoma - anaesthesia in a 12-year-old dog

In Feb 2010, I operated on the old dog with two pterygia in the right eye.

The case is described at:

Yesterday, Oct 19, 2011, I operated on this 12-year-old again. She was a happy dog as he wagged her short tail, unlike some dogs that had to be dragged into the vet surgery.

The pterygia had re-grown and covered the whole eye. Despite anti-glaucoma eye drops given by the medically knowledgeable owner, the glaucoma could not be cured. Now the ptergygia had covered the whole cornea as well, nearly 100%.

"I thought you spoke to the human eye expert regarding opening a hole in the sclera to drain the high eye pressure?" I asked her the day before yesterday when the dog was admitted. She had made a special appointment to see me at 10 am as she wanted me to do her dog's operation to take out the eyeball.

"In human glaucoma surgery," she said, "a stent has to be inserted into the eye to drain off the excess fluid."

"The dog will not tolerate a stent inside her eye," I said. So she gave the usual anti-glaucoma eye drops and they worked apparently. Till the pterygia over-grew the cornea by 100%. Eyeball enucleation was the only alternative.

Now the surgery is relatively easy but the main issue is that the vet must produce a dog alive at the end of surgery. Death on the operating table is not an option. I was much apprehensive about doing anaesthesia on this old dog, much beloved by the family members.

I had operated on a 16-year-old with several large circum-anal tumours. Just as I completed removal of the tumours, the dog's tongue turned snow white. There was no hope as there must be a rupture of the blood vessel in the inside, probably the liver as the total whiteness of the tongue meant massive bleeding usually.

This dog had liver disease as evident by the blood test. I wanted to postpone the operation to a Thursday, having put the dog on antibiotics for at least a week. However, the owners had to take leave and so I operated on a Monday as scheduled earlier. As to whether delaying by 3 days would make a difference to survival, it is not possible to forecast. Anaesthesia in old dogs are high risk and I don't take such cases unless the owners and family members are well aware of the tremendous risks involved. No vet cannot be 100% successful in anaesthesia of old dogs. Deaths on the operating table are extremely emotional and so I prefer not to operate but some cases just can't live a good quality of life without surgery.

As part of coaching of my assistant Mr Min, I will record what had been done for the benefit of vet students. In vet school, the anaesthetic theories are sound and if you adopt them to the letter, you are supposed to be successful.

In practice, the health and age of the old dog make veterinary anaesthesia highly risky as this will be the case in human anaesthesia. This is what I did for this old dog.

Oct 18, 2011. The dog was admitted. The owner said the dog ate well and was normal.

1. Blood test was taken.
2. No X-ray was done to reduce costs but X-ray of the chest and ECG are done in the Singapore General Hospital when I was operated on.
3. I gave an IV dextrose saline 500 ml + duphalyte 50 ml to this dog. IV baytril given.

1. Blood test was normal for this dog. This was good news.
2. Pre-op examination. The pulse quality was poor and the pulse was barely palpable. This was bad news. Other than that the temperature and respiration were normal.
3. Sedation. This is how I coached Mr Min on the dosage of Zoletil as I asked him to learn by writing on a piece of paper the dosage calculations.

The calculation is as follows:
In the dog, the maximum Zoletil 100 is 10 mg/kg. The dog weighed 24.5 kg and would need 245 mg. Therefore the volume of Zoletil 100 (100mg/ml) should be 245/100 = 2.45 ml.

However, I was using Zoletil 50. In theory, I should give 4.90 ml IV as Zoletil 50 is half the strength of Zoletil 100. Mr Min said he understood.

I took out a 1-ml syringe and gave the dog Zoletil 50 at 0.5 ml IV. This is 10% of the calculated dose. The 12-year-old dog was unable to stand 2 minutes after the injection. For a young dog, the dosage would be ineffective.

4. Isoflurane gas by mask 10 minutes later. 5% given initially.
"Check the left eyelid blinking reflex," I told Min as he was looking at the chest movements. "When the eye white (sclera) is seen, that means the dog is in surgical anaesthesia. That means the eyeball has rolled downwards. This is such a simple method of assessing the onset of surgical anaesthesia but many vet assistants don't use this method but rely on chest movements. "When chest movements stop," I said to Min, "It is already very serious heart failure. Put your finger onto the eyelids and see whether they blink."

It takes a lot of patience to repeat instructions to new people. Life is like that. Some know it faster than others. In human general hospitals you have the specialist anaesthetist to focus on anaesthesia but for vets in most practices, the sole responsibility is the vet surgeon.

5. Intubation. When the blink reflex was gone, I intubated this dog. However, she had problem taking the isoflurane gas by tube. Her chest movements were rapid and irregularly fast. I took out the tube, put on mask again. There was some froth seen in the endotracheal tube.

6. Atropine 0.5 ml IM and Lasix 1 vial 2 ml IV were given.

7. I intubated again. The dog reacted as if the tube was irritating. It gave vomiting sounds, as if one is clearing the throat. No vomitus. Yet the dog appeared to want to vomit. So I took out the tube and gave gas by mask.
The dog struggled to get up. "Give mask at 3% isoflurane, not 5%," I said to Min who was to be focused on anaesthesia. "It will take a long time at 3% but it is safer than 5%."

The dog kept curling his tongue upwards at one stage, during mask anaesthesia. Finally he was down to be operated. I cut 2 cm at the lateral canthus, cut the conjunctiva circumference of the sclera. The eyeball collapased but was taken out. I did not pull out the globe hard as this would traumatise the optic nerve and affect the eyesight of the normal left eye. The optic nerve could not be ligated. It was cut. Bleeding was profuse. Bleeding controlled by 5 swabs after cutting the eyeball and taking it out.

Nearly 1.5 hours due to the reactions of the old dog in being anaesthesized by intubation. He had some respiratory secretions and at one time, he panted or hyperventilated for over a few minutes. There are dogs that can't be anaesthesized using intubation which is the favoured ideal method of giving gas anaesthesia as they reacted to having a tube in their trachea. Why, I don't know. It happens in very rare cases. Changing to mask resolves the problem as in this case.

By mask, it was smooth and uneventful. The dog woke up immediately after the last stitch.

10. POST-OP. Tolfedine 2.5 ml IM and SC (2 parts). Baytril tablets 3 days. Then clavulox for another 10 days. Tolfedine tablets 5 days as painkillers.

11. GOES HOME IN THE EVENING. The dog was awake within 5 minutes after end of anaesthesia. E-collar. The eyeball was swollen but no bleeding. I had put in 2 layers. 2/0 absorbable PDS to stitch up the conjunctiva (cut edges after excising the eyeball circumferentially. Then I stitch up the eyelid (excised 3 mm margin leaving 0.5 mm of medial canthus eyelid uncut). Pictures shown. What the owner wanted was a dog alive and her trust that I could deliver. It was a happy ending.

I persisted in teaching Min how to carry the big dog without bending his back. I taught Nicole the 21-year-old girl who wanted to study vet medicine the same technique. Girls must carry big dogs too if they want to be a vet and equality and respect in this veterinary world!

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