For example, an Anesthesia resident will perform all of the procedures and monitor the patient's vital signs and response to the general anesthetics or other drugs. The Attending physician only intermittently checks on the case if the resident needs help or the case becomes too complicated.

If the resident doesn't bill for services performed, such as central line, placement, peripheral line placement, intubation, arterial lines, etc. I'm not sure who would do the billing.