We are doing survival surgery on the spinal cords of Sprague-Dawley rats but our animals are not surviving after surgery. We are using isoflurane for 5 minutes in the beginning to induce and then using an I.P injection of a ketamine/xylazine cocktail at 90mg/kg ketamine and 4mg/kg xylazine. We then move them to a cage with a heat lamp. We never had this issue before but now a majority of our rats are dying after the surgery is complete and we don't what we can adjust to keep them alive.
Contact your lab animal veterinarian and a boarded veterinary anesthesiologist (generally cool people who like to help). I am a veterinarian (not an anesthesiologist, with some experience in rat anesthesia for imaging and urogenital surgery, but not for spinal surgery). Double check the concentration (mg/mL) of your ketamine inj. (i.e.. 10, 20, 100? - just in case). Consider decreasing ketamine to 75mg. Titrate the drug to the mouse strain (not sure if there are any specific with regard to this strain). What percent iso are you administering via the precision vaporizor? Consider multimodal analgesia post i.e. with buprenorphine and an NSAID like carprofen (would require an adjustment of your IACUC if not previously accounted for. Check the heat lamp for any malfunction/ and double check that the distance from animal is not too close.
Not sure if this helps, best of luck
In my experience, it's the xylazine that is the culprit. It's a potent vasodilator, and especially if redosed, can cause the animal to become fatally hypotensive. Try eliminating the xylazine from your mixture. In addition, if your induction isoflurane concentration is too high it could also be overdosing the animals. If the xylazine is delivered not long after the iso, the double dose of vasodilators may be too much. Ketamine itself is a relatively safe drug - it's sympathomimetic. Although I don't know it's exact effects in rodents, in humans it is a potent analgesic and should assist with pain control in the post-operative period. I am an anesthesiologist.
1. You can try subcutaneous adminstration of normal saline (5-10ml) just after surgery( if you can not reduce the dose of Xylazine).
2. Keep the animals in ambient room temperature...
These two points have reduced mortality in guinea pigs (in my research) and I hope it is going to work in rats too..
I had a very high mortality when i keept them in the heating pad for a long time. So, don t use the lamp because you might be overheating them and the anesthesia blocks the termoregulation. Heating pad at 37 degress is the best, but swicht off sometimes if they have signs of hyperventilation.
I also add buprenorphine to the mix and use lower dose of ketamine (75mg/kg).
Good luck!
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