According to the director, 2.5 tons of blood was used throughout the production of the film.
In Germany, despite being released in theaters with the "not under 18" rating by the FSK, due to FSK's guidelines being a little more strict on home video than in theaters, rather than cut the movie to retain the FSK-18 rating, distributor Capelight Pictures decided to release the movie on Blu-ray in Germany with the light SPIO/JK rating instead.
In a flashback scene (1943) there is a digital vital sign machine operating in the surgery. These machines didn't exist in this form in the 1940s