"The physician is involved in the training of physician residents in a single anesthesia case, two concurrent anesthesia cases involving residents or a single anesthesia case involving a resident that is concurrent to another case paid under the medical direction rules. The physician meets the teaching physician criteria in §100.1.4 and the service is furnished on or after January 1, 2010;"
For services furnished on or after January 1, 1994, the physician can medically direct two, three, or four concurrent procedures involving qualified individuals, all of whom could be CRNAs, AAs, interns, residents or combinations of these individuals. The medical direction rules apply to cases involving student nurse anesthetists if the physician directs two concurrent cases, each of which involves a student nurse anesthetist, or the
physician directs one case involving a student nurse anesthetist and another involving a CRNA, AA, intern or resident.
For services furnished on or after January 1, 2010, the medical direction rules do not apply to a single resident case that is concurrent to another anesthesia case paid under the medical direction rules or to two concurrent anesthesia cases involving residents.
http://www4.cms.gov/manuals/downloads/clm104c12.pdf
page 112-144 There might also be other info in the link about this. I don't know that what I copy and paste answers your question. The claims processing manual is the first thing that came to mind so I started to search thru it.