Certified Registered Nurse Anesthetists (CRNAs) enroll in Medicare Part B as non-physician practitioners using the CMS-855I. However, CRNA Medicare billing is more complex than most provider types because the reimbursement rate and billing method depend entirely on the clinical arrangement — whether the CRNA is working independently, under general supervision, or under medical direction by an anesthesiologist.
Enrollment basics
- CRNA certification from the NBCRNA (current certification required)
- Master’s or Doctoral degree in nurse anesthesia
- State licensure as a CRNA or APRN
- Type 1 NPI (individual)
- Enrollment via CMS-855I or PECOS
Three billing arrangements
1. CRNA alone (no medical direction)
The CRNA provides anesthesia services without an anesthesiologist’s medical direction. The CRNA bills independently under their own NPI and receives 100% of the anesthesia fee schedule (anesthesia conversion factor × base units + time units).
The CRNA qualifies billing alone in states that have opted out of the physician supervision requirement via the governor’s opt-out letter to CMS. Check whether your state has opted out.
2. Medically directed (anesthesiologist + CRNA)
An anesthesiologist medically directs 2–4 CRNAs concurrently. Both the anesthesiologist and the CRNA bill, each receiving 50% of the allowable for their role.
For medical direction billing, the anesthesiologist must perform all seven required documentation steps (pre-anesthesia evaluation, presence at induction, presence at emergence, monitoring throughout, availability throughout, etc.). If any step is not met, the arrangement cannot be billed as medically directed.
3. Medical supervision (anesthesiologist + CRNA, >4 CRNAs)
When an anesthesiologist is involved with more than 4 CRNAs at once, it becomes medical supervision, not medical direction. The anesthesiologist’s billing is capped at 3 base units. The CRNA bills the full case.
Anesthesia billing basics
Anesthesia services are billed differently from most Medicare services:
- Base units — assigned to the anesthesia CPT code (varies by complexity)
- Time units — 1 unit per 15 minutes of anesthesia time
- Qualifying circumstances — add-on codes for unusual situations (controlled hypotension, emergency surgery, etc.)
- Conversion factor — the dollar value per unit (varies by locality)
⚠️ Risk flag: CRNA anesthesia time must be documented in the anesthesia record — start time (when CRNA takes over patient care) to end time (when CRNA transfers care). Undocumented or estimated time is the leading audit finding for anesthesia billing.
Hospital vs. ASC vs. office settings
- Hospital inpatient/outpatient: CRNA bills professional fee separately from facility fee
- ASC (ambulatory surgery center): Anesthesia professional fee billed separately; facility fee is bundled into ASC payment
- Office-based: All professional fees billed to Part B; office overhead not separately billable
Key applications
- CMS-855I — individual CRNA enrollment
- CMS-855R — reassignment to anesthesia group
Ask Mae if you have questions about medical direction documentation requirements, state opt-out status, or anesthesia billing units.