Where does it say in CPT that two physicians can’t bill for the same period of time when performing critical care?
It doesn’t. This is a Medicare rule.
There are two significant differences in critical care coding rules between CPT and CMS. (Wouldn’t our lives be easier if they were the same?)
The first is that CMS says one physician (and physicians in a group of the same specialty are considered one physician) cannot bill for ED visits and critical care in the same day. That isn’t a CPT rule. Here’s the citation for that.
“When critical care services are required upon the patient’s presentation to the hospital emergency department, only critical care codes 99291 – 99292 may be reported. An emergency department visit code may not also be reported.”
The second is this issue about billing for the same time period. The manual, quoted below, says that during any one single period of time, only one physician can bill for critical care, even if more than one is providing care.
“Only one physician may bill for critical care services during any one single period of time even if more than one physician is providing care to a critically ill patient.”
And of course, the care cannot be duplicative.
CodingIntel members can download the Critical Care Billing Guide for more detail.
 CMS Medicare Claims Processing Manual, 100-04, Chapter 12, Section 30.6.12 H
 CMS Medicare Claims Processing Manual, 100-04, Chapter 12, Section 30.6.12 F