42 CFR §414.40

1. (a)General rule. CMS establishes uniform national definitions of services, codes to represent services, and payment modifiers to the codes.
2. (b)Specific types of policies. CMS establishes uniform national ancillary policies necessary to implement the fee schedule for physician services. These include, but are not limited to, the following policies:
   1. (1)Global surgery policy (for example, post- and pre-operative periods and services, and intra-operative services).
   2. (2)Professional and technical components (for example, payment for services, such as an EEG, which typically comprise a technical component (the taking of the test) and a professional component (the interpretation)).
   3. (3)Payment modifiers (for example, assistant-at-surgery, multiple surgery, bilateral surgery, split surgical global services, team surgery, and unusual services).