Another way of thinking about whether you should capitalized the phrase is to consider the term nurse. It is not capitalized unless a name of a specific individual is mentioned after the term.

Is nurse a proper noun?

The noun registered nurse can be used as both a proper noun and a common noun.

Are job titles capitalized?

Titles should be capitalized, but references to the job are not. For instance, if you are using a job title as a direct address, it should be capitalized. ... Title references that immediately precede the person's name should also be capitalized.