It's in the CMS State Operations Manual, Appendix A, Survey, Protocol, Regulations and Interpretive Guidelines for Hospitals, which can be found
here.
Under the CoP for Surgical Services, see section A-0959 for CMS's interpretation of regulation 482.51(b)(6) that says the Op Note must contain at least:
• Name and hospital identification number of the patient;
• Date and times of the surgery;
• Name(s) of the surgeon(s) and assistants or other practitioners who performed surgical tasks (even when performing those tasks under supervision);
• Pre-operative and post-operative diagnosis;
• Name of the specific surgical procedure(s) performed;
• Type of anesthesia administered;
• Complications, if any;
• A description of techniques, findings, and tissues removed or altered;
• Surgeons or practitioners name(s) and a description of the specific significant surgical tasks that were conducted by practitioners other than the primary surgeon/practitioner (significant surgical procedures include: opening and closing, harvesting grafts, dissecting tissue, removing tissue, implanting devices, altering tissues); and
• Prosthetic devices, grafts, tissues, transplants, or devices implanted, if any.