42 C.F.R. § 416.46
Condition for coverage—Nursing services
The nursing services of the ASC must be directed and staffed to assure that the nursing needs of all patients are met.
(a) Standard: Organization and staffing. Patient care responsibilities must be delineated for all nursing service personnel. Nursing services must be provided in accordance with recognized standards of practice. There must be a registered nurse available for emergency treatment whenever there is a patient in the ASC.
(b) [Reserved]