I'm a CET (Certified Euthanasia Tech) and I just want to mention - it is unethical and in most states completely illegal under animal cruelty laws to do a cardiac injection of any kind unless the animal is under anesthesia at a surgical level (so deeply unconsious that the animal cannot feel pain on ANY level). Any vet that would perform this kind of injection without this level of anesthesia is using VERY bad practices. If they are going to do a cardiac injection and do not automatically knock your animal down, INSIST that they gas your animal down until there is no blink respose.
IP injections are actually very humane, and do not necessarily require the stress of masking an animal down. If they are done at the correct dose, the animal's brain shuts down in a specific order, taking the animal through the stages of anesthesia/unconsiousness before death (the med used in euthanasia was actually used as a surgical anesthetic for a long time, until they discovered better drugs that wore off faster), so it is literally like falling asleep. The drawback is that it takes a few minutes for this to work; it is slower but often less stressful. Cardiac and IV works essentially immediately (usually under 5 minutes) but IP generally takes 10-15 minutes if dosed correctly. (Sounds like this is the method used on your rat) However, if your animal is scared or stressed by the process of masking down with isoflorene, this is often the best euthanasia method because it is painless and low-key.
What is sounds like some of you experienced is the involuntary movement stage of surgical anesthesia - and this can be VERY disturbing to watch, especially if the drug was not dosed properly and this stage is longer than it should be. Stage 1 is when the animal is buzzed - this is the sedation level, you can compare it to when you get laughing gas at the dentist - you kind of know what is going on, but you aren't completely in control of yourself and you aren't extrodinarily worried about anything. Stage 2 is involuntary movement - you are unconscious, but your body moves without conscious input, either from reflexes or from uncontrolled signals from the brain. The goal in any anesthesia or euthanasia is to minimize this stage, because movement without intent is also movement without awareness of pain, and an animal could hurt itself unintentionally. But all anesthesia/euthanasia goes through this stage, you can't get surgical level or death without passing through this level of unconsciousness, so sometimes if an animal isn't dosed right or absorbs the drug a little too slowly then it stays in this stage long enough to be disturbing to watch (this is more likely when there are circulatory problems). Just realize that they CAN'T feel it, they don't know what's happening, and as scary as it is for us, it isn't scary at all for them - they don't even know. A lot of vets don't like giving IP in an owner-witnessed euthanaisa because it is by nature more slowly absorbed, and there is always a possibility of a stall in stage 2.
Euthanasia is not an easy thing, especially not for a pet-owner. Your vet should be sensitive to your emotional connection to your animal and do what they can to help ease the process - not everyone can watch, knowing what is happening, whatever the method used. However, it is important for you to know that done right, all these techniques, IV, IC, and IP can be done without pain and with a minimum of stress and fear for your animal. Usually this is much better than the pain of a slower death, and, whatever the form, the purpose of euthanasia is to give a release from that pain.
I recently had to euthanize one of my own chins, she had hyperplasia of her gums and was in a lot of pain, and although it was hard, I chose to do it myself so that I KNEW it was as kind and gentle as possible. She died with me right there, she was not afraid or in any additional pain. Knowing the mechanics of how modern euthanasia practices and the physiology behind it help me to know I did the best thing I could have for her. If you're like me and are interested in knowing what is happening, I'd encourage you to only trust reliable sources of information - there is a lot of misinformation out there.
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