Mary,
I think you are correct. I've been looking, and it appears that virtually all of the tube-feeding formulations are gluten free. Most of them contain maltodextrin, but in this country, maltodextrin, (unless stated otherwise on the label), is made from corn, (and sometimes potatoes). The only hitch is that medical compounds are exempt from the standard labeling laws. I'm not sure that tube-feeding solutions would be considered to be pharmaceuticals, (or medical compounds), since many of them are commonly available OTC, (examples are Boost, Ensure, etc.). Of course, many other meds and supplements, (including vitamin supplements), are available OTC, also, and we tend to be suspicious of them.
From a practical standpoint, I would say that the odds of gluten turning up as a feedstock source for the maltodextrin, would be practically zero at this point in time. The reason I say this is because wheat is always priced higher than corn, and it is historically high this year, at two to three times it's normal long-term price. Typically, the price of wheat, to the farmer, is in the $3 to $4 category. It is now worth around $8 per bushel, and the price continues to climb. Corn, on the other hand, is also historically high, but it is priced around the $3 per bushel level, so no manufacturer in his right mind is going to use wheat for a product that can be made from corn.
I'm not sure about NSAIDS in general, but plain old asprin has always been available in powder form, which means that it is easy to put into solution. Whether or not a hospital would do that, I wouldn't venture to guess. The few times that I've been in a hospital, and in need of pain medication, they always used morphine, by IV, or pills with a combination of hydracodone and acetaminophen. If they had slipped something into the IV, though, I wouldn't have had a clue.
I think it's a good idea. If they at least notice it, it should cause anyone treating you to be more alert about what they do, and it clearly shows that you are concerned about how you are to be treated.
Tex