If the documentation supports the physician met the medical direction criteria for the cases he was involved in he could report with the start and end times from the anesthesia record is my understanding.
http://www.cms.gov/manuals/downloads/clm104c12.pdf
Page 120
Payment at the Medically Directed Rate
The Part B Contractor determines payment for the physician's medical direction service furnished on or after January 1, 1998, on the basis of 50 percent of the allowance for the service performed by the physician alone. Medical direction occurs if the physician medically directs qualified individuals in two, three, or four concurrent cases and the physician performs the following activities.
• Performs a pre-anesthetic examination and evaluation;
• Prescribes the anesthesia plan;
• Personally participates in the most demanding procedures in the anesthesia plan, including induction and emergence;
• Ensures that any procedures in the anesthesia plan that he or she does not perform are performed by a qualified anesthetist;
• Monitors the course of anesthesia administration at frequent intervals;
• Remains physically present and available for immediate diagnosis and treatment of emergencies; and
• Provides indicated-post-anesthesia care.
Prior to January 1, 1999, the physician was required to participate in the most demanding procedures of the anesthesia plan, including induction and emergence.
For medical direction services furnished on or after January 1, 1999, the physician must participate only in the most demanding procedures of the anesthesia plan, including, if applicable, induction and emergence. Also for medical direction services furnished on or after January 1, 1999, the physician must document in the medical record that he or she performed the pre-anesthetic examination and evaluation. Physicians must also document that they provided indicated post-anesthesia care, were present during some portion of the anesthesia monitoring, and were present during the most demanding procedures, including induction and emergence, where indicated.