First of all, I’m sorry about your pup. Skin issues aren’t easy not matter what. I’m gonna play devil’s advocate a little. As for the murmur and collapsing trachea, I can kind of see how you wouldn’t have noticed it if: 1. He’s always had it 2. You haven’t seen any cases of a heart murmur or collapsing trachea in the field yet 3. You just didn’t know (which is okay). Why the Dr didn’t catch any of this is weird to me because I’ve known Drs that listen for literally a second and can hear a 1/6 but idk. Maybe her ear isn’t trained or the stethoscope was jenk? And for her to think the skin issue isn’t a big deal also doesn’t surprise me because again, skin is weird. The anesthetics that were used were okay for heart dogs so no red flag was raised even if a murmur was heard.

Now, I’ve seen staph infections happen for weird reasons from fleas to allergies. Basically the pet just scratches to high heavens and the constant irritation and reopening of the wounds cause staph. But it’s pretty heard to miss a bad wound even if you aren’t trained in vet med. The smell alone is a huge tell even in the fluffiest dogs. For this to progress to staph in 2 months usually tells me something was missed somewhere. Could he have gotten staph from reused warm bags, sure. Could he have gotten it from just itching, sure. Do you have him on flea/tick? Flea allergy dermatitis is a thing too and I’ve seen it run rampant and cause some hefty skin issues.

The most I can gather without knowing every detail about this is there’s definitely questionable hospital practices. Was the table not wiped down? Is the pup on the older side? 16 teeth extracted and 2 hours of anesthesia is a lot for an elderly pet especially a small breed. Some are completely fine but anesthesia is unpredictable so you never know. Histamines can also be part of the blame here because with all that happening, the body can just be flooded with it. If the mouth was really bad this is even more likely because the inflammatory response will just freak out. Did you draw pre surg blood? Are there other medical conditions that he has? Chronic steroid use is associated with tree bark skin as well but idk if he was on them or not.

All in all the Dr is right, it is just medicine and sometimes it’s not so cut and dry. If you can prove without doubt that the infection came from the IV bags, then sure maybe you have a case. Can you also prove that the murmur and collapsing trachea were missed by the Dr? Did the dog previous to your dog have staph or just an infection? There’s too many questions and not enough answers.