You should cite an UpToDate topic as follows:
Marion, DW. Diaphragmatic pacing. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on November 25, 2013.)
If you are using EndNote, choose Book Section as your Reference Type. Enter the Publisher (UpToDate), Place Published (Waltham, MA) and Accessed Date in the same field. See example below:
Learn more about EndNote from our EndNote Guide Online.