Question relating to vampires?

No. Blood does not contain the amounts of needed nutrients to sustain a human sized creature. Furthermore, iron in blood consumed can cause iron toxicity, which can be lethal. In most cases ingested blood is expelled violently from the body via projectile vomiting. Even if a human sized creature could retain the ingested blood, it would need to consume the entire blood supply to even begin to take in needed amounts of what nutrients there are in blood, and the human form cannot do that - the stomach is far too small. Lastly, ingested blood would have to be expelled via the intestines - and would come out as a black, gelatinous, oozing mass that the vampire would have little control over - it would be constantly oozing sanguinous waste and would smell horrible.

I am a Nurse.

Technically, yes, but not forever. The Huns would survive for weeks at time on the blood and milk of their horses.

No, a human cannot survive on a strict diet of blood. Our bodies require much more than blood can provide in order to survive.

Vampires (and the bats named after them) are the only critters that survive solely on blood. Vampires are fantasy creatures, which means they don't have to follow any rules of reality. Real people, on the other hand, do have to follow those rules.