Anesthesia does not bill like the rest of medicine. There is no fee per procedure. Payment is a formula. The modifiers decide who is paid and how much. And the documentation behind them sits in a record the biller usually cannot see. That combination is why anesthesia groups either bill very well or lose a great deal without noticing.
Our anesthesia billing services cover physician-only groups, care team models and CRNA-only practices. We handle the enrollment side too. Groups comparing anesthesia medical billing services should ask one question first. Who checks that the medical direction modifier matches the record?
The payment formula
(Base units + time units + modifying units) × conversion factor
Base units are assigned to each ASA procedure code and reflect its complexity. Time units run from when you begin preparing the patient to when you are no longer in personal attendance. That time is divided into units, commonly 15 minutes each. The divisor is set by the payer contract, so it is not the same everywhere. The conversion factor is a dollar amount per unit, again per contract.
- Anesthesia time must be documented as actual start and stop times. Rounded or reconstructed times are the classic audit finding.
- When multiple procedures are performed, you bill the code with the highest base units, not all of them.
- Some payers pay physical status and qualifying circumstance units; many commercial plans do not. That belongs in the contract review, not in a monthly denial report.
Medical direction modifiers
This is where the money is, and where the mistakes are.
| Modifier | Meaning | Effect |
|---|---|---|
| AA | Anesthesia personally performed by the anesthesiologist | Full payment to the physician |
| QK | Medical direction of two, three or four concurrent procedures | Split payment: physician portion |
| QX | CRNA service with medical direction by a physician | Split payment: CRNA portion |
| QZ | CRNA service without medical direction | Full payment to the CRNA |
| QY | Medical direction of one CRNA by an anesthesiologist | Split payment |
| AD | Medical supervision, more than four concurrent procedures | Reduced payment |
QZ versus QK/QX is the single highest-value decision in anesthesia billing. Medical direction requires the anesthesiologist to meet seven conditions, documented for each case. A pre-anesthetic evaluation. Prescribing the plan. Taking part personally in the demanding sections. Staying physically available. Monitoring at frequent intervals. Doing nothing else that would interfere. And the post-anesthesia care. If those conditions are not documented, the claim should not carry a direction modifier. Billing direction that the record does not support is a recognized audit target with refund exposure.
Other things that decide the claim
- Physical status modifiers P1 to P6, where the payer recognizes them.
- Qualifying circumstances: extreme age, emergency, hypothermia, controlled hypotension.
- Monitored anaesthesia care: QS, G8 and G9 as the payer requires, with the medical necessity for MAC documented.
- Labor epidurals. Payers differ widely here: some pay by time, some a flat fee, some a capped formula. Getting the contract term right matters more than the coding.
- Post-operative pain blocks are billed separately when the block is not the anaesthetic itself. The record has to show the surgeon asked for it.
CRNA credentialing and group enrollment
Credentialing an anaesthesia group is a roster exercise rather than a single application:
- Each anaesthesiologist and each CRNA enrolls individually and reassigns benefits to the group. CRNAs enrol with Medicare under their own NPI. When they are not medically directed, they are paid the same rate as a physician for the service.
- State scope of practice varies considerably for CRNAs, including whether physician supervision is required, and payers ask about it.
- Facility privileges are separate from payer contracts and are granted by each hospital and ASC on its own cycle.
- Groups covering several facilities need each location on the enrollment, and locum coverage needs its own arrangement.
- Out-of-network anaesthesia at an in-network facility is exactly the situation the surprise billing rules address, so network status per facility should be known and documented rather than assumed.
See our medical credentialing services for the roster and facility enrollment work.
What we do every week
- Case capture reconciliation against the facility schedule, so no case is billed late or not at all.
- Time and unit calculation using each payer's own divisor and conversion factor.
- Modifier assignment with the direction conditions checked against the record.
- Claim submission and clearinghouse rejection work.
- Denial management and appeals.
- Payment posting and underpayment checks against the contracted conversion factor.
- Roster monitoring so a departed CRNA is never the rendering provider on a claim.
- Monthly reporting on units per case, conversion factor realised and denial reasons.
Anesthesia billing FAQs
Should we bill QZ or QK/QX?
It depends entirely on whether the anesthesiologist met and documented all seven medical direction conditions for that case. QZ is correct for a CRNA practicing without medical direction. The decision is a documentation question, not a revenue preference, and it should be audited regularly.
How are anesthesia time units counted?
From the start of preparing the patient for anaesthesia to when the anaesthetist is no longer in personal attendance, divided into units. The divisor is commonly 15 minutes but is set by the payer contract, so a single global setting in the software will underbill some payers and overbill others.
Do commercial payers pay physical status units?
Many do not. It is a contract term rather than a coding rule, which is why we check it at onboarding rather than discovering it through a pattern of zero-paid lines.
Can you bill a post-op pain block separately?
Yes, when the block is for post-operative analgesia rather than being the anaesthetic itself, and the surgeon's request is documented. Blocks used as the anaesthetic are part of the anaesthesia service.
Talk to an anesthesia biller
Send us a month of cases and your contracted conversion factors. We will show you the unit gap and the modifier exposure.
Schedule a billing demo Talk to a billing expert