I wish I could give you technical information, since that's what you asked for, but I don't have any answers to your questions, especially since I don't know if the procedures are the same there in Ireland as they are here - for instance, in the US cat neuters are quick and easy, taking only minutes, since all that is done is removal of the spermatic cord. Therefore, anesthesia is a very short-acting sedative, not involving paralyzation. Complications from and reactions to the anesthesia are very rare. But perhaps in Ireland a full castration is done, which would probably require deeper anesthesia and maybe (but probably not) intubation. Nevertheless, a reaction can still occur. Even then, I can't imagine what would have happened to his eyes. Deep, long anesthesia in humans sometimes requires some kind of eye protection, so I've heard, but a simple neuter surely wouldn't have. The fact that he vomited is not really that big of a deal - in fact, it's expected - which is why they are fasted and thirsted for a period before the surgery.

But, anyway, I'm praying for you and poor little Merlin, and hope he continues to improve. I would be so scared if one of my cats quit breathing! I'm glad you were aware of a technique that would revive him.