If his lungs were in danger of failing he'd be hooked up to a lot more than an oxygen mask and the IV drip is a cure for dehydration when oral supplementation of water won't act quickly enough or the patient is not capable of taking them, say someone unconscious. Of course sometimes there are medications and such mixed in with the IV so that they will act quickly but other than pain killers I can't see anything like that being necessary for us. Of course Gren likely doesn't know that and it is reasonable that he would think that Shiro does need the things.

But you say you did move him to the dorm, which is not what it says in your post, it says that you took him to the infirmary and hooked him back up, and if you have visited the dorms at some point you wouldn't have had to search for Sapphire cause Gren would have seen her either sleeping or reading in her bunk depending on the time.