Praise be to Allah.
All hospitals have to ensure that male nurses treat men and female nurses treat women. This is obligatory, just as it is obligatory for male doctors to treat men and female doctors to treat women, except in cases of extreme necessity. If the treatment for an illness is only known by a man it is OK for him to treat a woman, because this is a case of necessity. Similarly, if the treatment for a man's illness is only known by a woman, it is OK for her to treat him. Otherwise, male doctors must treat men and female doctors must treat women. This is obligatory. The same applies to nurses, both female and male. Male nurses should treat men and female nurses should treat women, so as to avoid the means that may lead to fitnah (temptation) and to prevent khulwah (being alone with a non-mahram member of the opposite sex).