Why would a cat die after being spayed/neutered and vomiting yellow fluid?

Vomiting yellow fluid after neutering is usually an anesthetic reaction and generally recovers within 12 to 24 hours; during this period you can give the cat anti-emetic medication to ease the vomiting. But if the cat still vomits yellow fluid frequently 2 to 3 days after surgery, it may be an anesthetic overdose that has irritated its stomach, and it needs prompt fluid therapy to speed up metabolism of the anesthetic in its body.

If a cat dies after vomiting yellow fluid post-neutering, it is more likely caused by a feline panleukopenia (distemper) infection. Because the owner did not vaccinate the cat regularly, it caught distemper after surgery and died from delayed treatment.