Anesthesia care team models: ratios, rules and what each costs

The ratio of anesthesiologists to anesthetists in your operating rooms is one of the biggest drivers of what anesthesia costs your hospital. Many executives inherit a staffing model from their anesthesia group and never see the arithmetic behind it.

This guide explains the main anesthesia care team models, how Medicare pays for each, and what drives cost. It takes no side on which clinicians are best. Anesthesiologists, certified registered nurse anesthetists (CRNAs) and certified anesthesiologist assistants (CAAs) all deliver anesthesia every day. The right mix depends on your hospital.

A note on terms: the American Society of Anesthesiologists (ASA) uses "anesthesia care team" for a team led by a physician anesthesiologist.¹ We use "model" for any way of staffing anesthesia.

Five ways to staff anesthesia

Physician-only. An anesthesiologist personally provides each anesthetic, one room at a time.

Care team with medical direction. One anesthesiologist directs CRNAs or CAAs in up to four rooms at once, with an anesthetist in each room. The ratio, written 1:2, 1:3 or 1:4, is rooms per anesthesiologist.

Medical supervision. The same structure, but the anesthesiologist covers more than four rooms at once or takes on other work that breaks the medical direction rules.

CRNA-only. CRNAs provide anesthesia without an anesthesiologist directing the case.

Care team with CAAs. CAAs work under an anesthesiologist's direction, in states that allow them to practice.

Model	Modifiers billed	How Medicare pays the case23
Physician-only	AA	Full allowance to the anesthesiologist
Medical direction, 1:1	QY (anesthesiologist), QX (anesthetist)	50% to each
Medical direction, 1:2 to 1:4	QK (anesthesiologist), QX (anesthetist)	50% to each
Medical supervision, more than four rooms	AD (anesthesiologist)	Anesthesiologist gets three base units, plus one time unit if present at induction
CRNA-only	QZ (CRNA)	Full allowance to the CRNA

Medical direction vs medical supervision: how Medicare pays

Medical direction is a billing status, not just a staffing pattern. For each patient, the anesthesiologist must do the pre-anesthetic exam, prescribe the plan, take part in the most demanding parts (including induction and emergence, where they apply), ensure a qualified person does anything they do not, monitor at frequent intervals, stay physically present and available for emergencies, and provide post-anesthesia care. They may direct no more than four cases at once.⁴

When those conditions are met, Medicare splits one fee. The anesthesiologist and the anesthetist each receive 50% of what Medicare would pay if the anesthesiologist had done the case alone.² So Medicare pays the same total for a medically directed case as for a personally performed one. What changes is how many clinicians share it.

Medical supervision pays less. If the anesthesiologist covers more than four concurrent cases, or performs other services while directing, Medicare allows only three base units per case, plus one time unit if they document presence at induction.³ Some tasks do not break medical direction: a short emergency nearby, placing a labor epidural, periodic monitoring of an obstetric patient, checking recovery room patients and handling scheduling.³

A CRNA working without medical direction bills with QZ and is paid under the same formula as an anesthesiologist working alone, with no 50% reduction.² QZ is defined for CRNA services; CAAs work under an anesthesiologist's direction.²

One naming trap: the AA modifier means the anesthesiologist personally performed the case. It has nothing to do with anesthesiologist assistants.³

Commercial payers set their own rules, so check each contract.

What drives the cost to the hospital

Your anesthesia cost is, roughly, the cost of the coverage you ask for minus what the group collects for it. When collections fall short, the gap comes back to you as a subsidy. Four things set that cost.

Clinician mix. Every step from 1:4 toward physician-only adds anesthesiologists. Medicare's total payment for a directed case does not rise to match.

Coverage hours. You pay for staffed rooms, not busy ones. A room staffed until 5 p.m. that finishes at 2 costs the same as a full one.

Achievable concurrency. A 1:4 ratio on paper means little if critical moments collide. In a year of data from one tertiary care hospital, a 1:2 ratio still produced at least one supervision lapse on 35% of days, mostly before 8 a.m. The authors found that moving from 1:2 to 1:3 has a large effect on lapses at first-case starts, and that staggered starts or extra anesthesiologists early in the day would be needed.⁵ Many short cases, or rooms on different floors, push the achievable ratio down further.

Call coverage. Nights, weekends, obstetrics and trauma need someone available whether or not cases come, and quiet hours bring in less billing.

An illustrative example: 12 rooms

The table uses made-up figures for 12 anesthetizing locations running at once, counting only the clinicians needed in those rooms.

Model	Anesthesiologists	CRNAs or CAAs	Total clinicians
Physician-only	12	0	12
Medical direction, 1:2	6	12	18
Medical direction, 1:3	4	12	16
Medical direction, 1:4	3	12	15
CRNA-only	0	12	12

Moving from 1:2 to 1:4 halves the anesthesiologist count, from six to three. Staffing is lumpy: close one room and 1:3 still needs four anesthesiologists, while 1:4 still needs three. And real schedules need more people for break relief, pre-op or a block room, late rooms, obstetrics and call. Those needs add to every row.

CRNA supervision, opt-out states and CAAs

Federal hospital rules require a CRNA to be supervised by the operating practitioner or by an anesthesiologist who is immediately available, unless the state is exempt. A CAA must be supervised by an anesthesiologist who is immediately available; the exemption does not cover CAAs.⁶ This "supervision" is a hospital condition of participation, not the "medical supervision" billing category.

A state opts out when its governor sends CMS a letter, after consulting the state boards of medicine and nursing, attesting that opting out is in the citizens' best interests and consistent with state law. It takes effect on submission.⁶ Parallel exemptions cover critical access hospitals and ambulatory surgery centers.⁷⁸

Counts depend on the source and date. CMS's own page still gives a count as of November 2020: nineteen states and Guam.⁹ The American Association of Nurse Anesthesiology (AANA) lists 27 states and Guam as of 2026, including Vermont and Ohio in July 2026. Utah and Wyoming are partial opt-outs, limited to critical access hospitals and certain rural or small hospitals.¹⁰ The ASA's list names the same 27 states.¹¹

Opting out removes a federal facility requirement. It does not change state scope-of-practice law or Medicare's conditions for billing medical direction. The ASA and AANA hold opposing views on opt-out, and we take no side. What matters is what your state law and medical staff bylaws allow today.

CAA counts vary too. The American Academy of Anesthesiologist Assistants says CAAs can practice in 22 states, Washington, D.C., and Guam.¹² The ASA's list, last updated September 2025, names 24 jurisdictions.¹³ CAA supervision ratios vary by state,¹⁴ so confirm current law before planning around them.

How to choose the right model

No model is right everywhere, and different areas of one hospital may need different models. Start with four questions.

What is your case mix? Short, fast-turnover cases limit concurrency. Sicker patients and complex procedures can demand more of whoever leads the anesthetic, which may argue for a lower ratio in those rooms.

What does obstetrics need? A labor floor needs coverage around the clock, whatever the volume. Medicare's medical direction rules make room for labor epidurals and periodic obstetric checks.³ Smaller units often staff differently. In a national survey conducted in 2012, independent CRNAs provided obstetric anesthesia in 68% of hospitals with fewer than 500 births a year.¹⁵ In the survey's latest update, obstetric anesthesia providers at nonacademic hospitals were more likely than academic ones to have other clinical responsibilities (62% versus 35%).¹⁶

Do you run trauma or heavy emergency surgery? Someone must be available at all hours. Decide who covers, in-house or on call, and price it separately.

Who can you recruit? A model fails if you cannot hire for it. Look at which clinicians your market can supply and keep. See our overview of the anesthesia staffing shortage.

Sources

1. American Society of Anesthesiologists, "Statement on the Anesthesia Care Team," ASA Standards and Practice Parameters, October 2023. https://www.asahq.org/standards-and-practice-parameters/statement-on-the-anesthesia-care-team ↩

2. Centers for Medicare & Medicaid Services, "Medicare Claims Processing Manual, Chapter 12, Section 140: Qualified Nonphysician Anesthetist Services," CMS Internet-Only Manual (Rev. 13316), July 2025. https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c12.pdf ↩ ↩² ↩³ ↩⁴

3. Centers for Medicare & Medicaid Services, "Medicare Claims Processing Manual, Chapter 12, Section 50: Payment for Anesthesiology Services," CMS Internet-Only Manual (Rev. 13316), July 2025. https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c12.pdf ↩ ↩² ↩³ ↩⁴ ↩⁵

4. Centers for Medicare & Medicaid Services, "42 CFR 415.110, Conditions for Payment: Medically Directed Anesthesia Services," Electronic Code of Federal Regulations, current text. https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-B/part-415/subpart-C/section-415.110 ↩

5. Epstein RH, Dexter F, "Influence of Supervision Ratios by Anesthesiologists on First-Case Starts and Critical Portions of Anesthetics," Anesthesiology, March 2012. https://pubmed.ncbi.nlm.nih.gov/22297567/ ↩

6. Centers for Medicare & Medicaid Services, "42 CFR 482.52, Condition of Participation: Anesthesia Services," Electronic Code of Federal Regulations, current text. https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-G/part-482/subpart-D/section-482.52 ↩ ↩²

7. Centers for Medicare & Medicaid Services, "42 CFR 485.639, Condition of Participation: Surgical Services," Electronic Code of Federal Regulations, current text. https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-G/part-485/subpart-F/section-485.639 ↩

8. Centers for Medicare & Medicaid Services, "42 CFR 416.42, Condition for Coverage: Surgical Services," Electronic Code of Federal Regulations, current text. https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-B/part-416/subpart-C/section-416.42 ↩

9. Centers for Medicare & Medicaid Services, "Spotlight" (Anesthesia Supervision section), CMS Conditions for Coverage & Conditions of Participation, May 2026 (page last modified; count stated as of November 2020). https://www.cms.gov/medicare/health-safety-standards/conditions-coverage-participation/spotlight ↩

10. American Association of Nurse Anesthesiology, "Fact Sheet Concerning State Opt-Outs and November 13, 2001 CMS Rule," AANA, July 2026. https://www.aana.com/wp-content/uploads/2023/10/Fact-Sheet-Concerning-State-Opt-Outs-July-2026.pdf ↩

11. American Society of Anesthesiologists, "Opt-Outs," ASA Advocacy, undated (lists opt-outs through July 2026). https://www.asahq.org/advocacy-and-asapac/advocacy-topics/opt-outs ↩

12. American Academy of Anesthesiologist Assistants, "Certification Practice Map," AAAA, undated. https://www.anesthetist.org/certifcation-practice-map ↩

13. American Society of Anesthesiologists, "Anesthesiologist Assistants," ASA Advocacy, September 2025. https://www.asahq.org/advocating-for-you/anesthesiologist-assistants ↩

14. American Society of Anesthesiologists, "Statement on Certified Anesthesiologist Assistants (CAAs): Description and Practice," ASA Standards and Practice Parameters, October 2022. https://www.asahq.org/standards-and-practice-parameters/statement-on-certified-anesthesiologist-assistants-description-and-practice ↩

15. Traynor AJ, Aragon M, Ghosh D, Choi RS, Dingmann C, Vu Tran Z, Bucklin BA, "Obstetric Anesthesia Workforce Survey: A 30-Year Update," Anesthesia & Analgesia, June 2016. https://pubmed.ncbi.nlm.nih.gov/27088993/ ↩

16. Bucklin BA, Hawkins JL, Asdigian NL, Kennerley V, Pattee J, Traynor AJ, "Obstetric Anesthesia Workforce Survey: Forty-year Update," Anesthesiology, August 2025. https://pubmed.ncbi.nlm.nih.gov/40237779/ ↩