Critical Care is a food replacement made by Oxbow for ailing or underweight herbivores. Sometimes chins are happy to eat it off of a spoon or out of a bowl, and other times you need a syringe to feed it. Make sure you get a syringe that has a catheter or large tip on it so the CC can squeeze through.
You don't need to trust the E-vet for it. It's pre-packaged and sealed, so nothing he/she needs to even touch. If you can't get it there, maybe call around and try and find a package locally.
If you absolutely can't, then you can try and grind up your own pellets into a fine powder. You can add some canned pure pumpkin and/or some black strap molasses, as well as some water to get it to a consistency that you can feed. Right now, he may be so ill that even chewing is more activity than he can deal with. That's where the syringe comes in handy. It takes some practice to hand feed, but once you have it down it's not so bad.
If you do need to hand feed, most chins fight it tooth and nail, even if they like the stuff. In that case, you would need to wrap up your chin in a thin towel, making sure that all four feet are covered, so they can't kick out and knock the syringe away or struggle. I lay a towel across my chest (I use a really thin towel, like a shop rag), then put the chin on the towel, closer to one side. I quickly wrap the short side around to trap the legs, then wrap the rest of the towel around to secure it. I then hold the chin's head between my thumb and second finger, with my first finger on the top of their head, while holding their body between my forearm and the side of my body. It gives me a lot better control and they don't struggle and get upset. Then you just put the syringe in behind their front teeth, into the gap that's there, and squirt in a little bit of CC. The first few times I've ever had to use it, the chins act like it's poison. You need to persist, especially if he's losing weight already or hasn't regained weight from a previous illness. Depending on his current weight, bare minimum for a daily feeding amount would be 50 mL. When I hand feed, I generally do at least 100 mL per day, broken into 2 feedings, morning and night.
