First, I am glad that you didn't add any and hopefully there wasn't much in the sauce. The reason I ask is because both are cat toxic and can cause GI upset as well as delayed (days to weeks later) onset anemia. So, we'd want to keep an eye on those gums this week to just make sure those don't change. Otherwise, in a situation of this nature, our approach does depend on the severity of their nausea. If a cat is vomiting profusely, cannot keep even water down, are dehydrated, or has any of those signs I asked about; then those tend to be our cue to have the cat seen.
Still, since he sounds more settled then that, we can try some home supportive care to try to settle his stomach. To start, if he hasn’t just vomited (since otherwise we’d need to rest his stomach for a few hours first), then you can consider treating him with an antacid. Common OTC pet safe options would be Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid), or Tagamet (More Info/Dose Here @ http://www.petplace.com/article/drug-library/library/over-the-counter/cimetidine-hcl-tagamet). Whichever you choose, we’d give this 20 minutes before offering food to allow absorption. Of course, do double check with your vet if he has a known health issues or is on any medications you haven't mentioned. Though if you give this and he cannot keep it down due to nausea that is usually a red flag that we need to bypass his mouth with injectable anti-vomiting medication from his vet.
Once that has had time to absorb and he is steadier on his stomach, you can consider starting him on a light/easily digestible diet. Examples you can use are boiled chicken, boiled white fish, or scrambled eggs (made with water and not milk). There are also OTC vet diets that can be used (ie Hill’s I/D or Royal Canin’s sensitivity) too. The aim of these diets is that they will be better tolerated/absorbed by the compromised gut. Therefore, it should get more nutrients in and result in less GI upset. As long as improvement is being seen, I usually advise continuing this until the signs are settled, and then weaning him slowly back to his normal diet.
Since dehydration is a risk in vomiting cases, we need to keep an eye on his hydration. To check this and ensure he’s not becoming dehydrated, there are a few things you can test. Further to checking for gum moisture, you will want to make sure his eyes are not looking sunken and that he doesn’t have a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a good video HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you are seeing any signs of dehydration already, then that would be our cue to have him seen before this becomes an additional issue for him (especially as it is often dehydration that makes them feel unwell).
Overall, we do need to tread with care in cases of nausea and anorexia in cats. Still, if he doesn’t’ have those other signs, we can consider trying supportive care to settle his stomach. Of course, if he can’t keep that or water down, appears dehydrated already, or doesn’t respond to the above within 12-24 hours; then we'd want to get his vet involved. They can assess his hydration and start him on symptomatic treatment (ie injectable anti-vomiting medication, fluids, etc) to get him settled.
Please take care,
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