CPT code 00104: Anesthesia for electroconvulsive therapy

Key Takeaways

CPT code 00104 is the anesthesia code for electroconvulsive therapy (ECT), billed by the anesthesiologist or CRNA (certified registered nurse anesthetist).

Base unit value is 4, per the American Society of Anesthesiologists (ASA) Relative Value Guide; Medicare fixes anesthesia time at 1 unit (15 minutes) for CPT 00104 regardless of case length, so a Medicare claim totals 5 units.

The psychiatrist bills CPT 90870 for the ECT procedure itself; double-billing both codes under one provider is a common denial trigger.

Practice management software like Pabau keeps the anesthesiologist’s and psychiatrist’s ECT documentation in one patient record, so any provider on the account can reference the psychiatrist’s diagnosis code directly instead of requesting it separately.

A full course of electroconvulsive therapy (ECT) can run 6 to 12 sessions, and each one can generate two separate claims from two different providers. When the anesthesia side of that split gets coded wrong, the denial rarely shows up until the remittance advice arrives weeks later.

CPT code 00104 sits at the center of that problem. It’s the code the anesthesiologist or nurse anesthetist reports for sedating a patient through ECT, and it runs on anesthesia math that trips up even seasoned billers.

This guide walks through CPT code 00104 end to end: its official descriptor, base units and RVU calculation, the 2026 Medicare fee schedule, applicable modifiers and add-on codes, the CPT 90870 split, and the billing errors most likely to cost you a payment.

CPT code 00104: Definition and official descriptor

CPT code 00104 covers anesthesia services provided during electroconvulsive therapy procedures. The official American Medical Association (AMA) descriptor is: Anesthesia for electroconvulsive therapy.

ECT is primarily used for treatment-resistant major depressive disorder (MDD), bipolar disorder with severe depressive or manic episodes, and catatonia.

Because most patients receive general anesthesia or monitored anesthesia care (MAC) during each session, anesthesia services are billed separately from the ECT procedure itself. CPT code 00104 is the billing code used by the anesthesiologist or the certified registered nurse anesthetist (CRNA) providing that care.

This code sits within the broader anesthesia section of the CPT code set, which the AMA maintains and updates annually. ECT sessions are typically brief (5-15 minutes of stimulation time), but the anesthesia period covers pre-induction monitoring through post-procedure recovery, often totaling 30-45 minutes of anesthesia time.

Anesthesia base units and RVU

Anesthesia billing uses a units-based formula rather than the standard work relative value unit (RVU) model. The total reimbursable units combine base units assigned to the procedure with time units accrued during the case.

The same base-plus-time structure applies across the anesthesia code set, from CPT 00170 for intraoral procedures in the same head-anesthesia range as 00104, to CPT 01850 for forearm and hand surgery.

Formula: (Base Units + Time Units) x Conversion Factor = Reimbursement

For most anesthesia codes, time units scale with how long the case runs. CPT 00104 is a documented exception: Medicare’s long-standing anesthesia billing convention caps time-unit billing at exactly one 15-minute unit for CPT 00104, regardless of how long the anesthesia case actually lasts.

Commercial payers don’t always follow this fixed convention – some calculate time units from actual elapsed minutes instead, so confirm the payer contract before assuming the Medicare rule applies.

CPT 00104 fee schedule and reimbursement rates 2026

Medicare reimbursement for CPT 00104 is calculated using the anesthesia conversion factor multiplied by total units. Rates differ by geographic locality through the CMS Geographic Practice Cost Index (GPCI), the same locality adjustment applied to other anesthesia codes like CPT 01400 for knee-joint procedures.

The figures below reflect general ranges; confirm exact amounts through the CMS Physician Fee Schedule lookup for your MAC jurisdiction.

Commercial payer rates vary significantly, and unlike Medicare, many commercial payers don’t fix anesthesia time at a single unit for CPT 00104 – they calculate time units from the actual anesthesia minutes recorded instead.

The Medicare figures above use the approximate CY2026 national anesthesia conversion factor of $20.50 per unit (non-Qualifying APM); actual locality payments depend on GPCI adjustments. Verify current rates annually, as CMS updates fee schedules each January 1.

Medicare and Medicaid coverage

Medicare covers ECT and the associated anesthesia (CPT code 00104) when the service is medically necessary. Coverage is typically supported by mental health EMR documentation demonstrating that the patient has not responded to adequate trials of pharmacotherapy. Coverage criteria generally include:

• Diagnosis of treatment-resistant major depressive disorder, bipolar disorder with severe episodes, or catatonia
• Documented failure of at least one adequate antidepressant trial (dosage and duration per clinical guidelines)
• Attending psychiatrist order for ECT, with a pre-procedure evaluation on file
• Anesthesia pre-assessment completed and documented by the anesthesia provider
• Each session billed separately; Medicare typically covers ECT series for acute treatment phases

Medicaid coverage for ECT anesthesia varies by state. Some state Medicaid programs require prior authorization for ECT series. Others apply different reimbursement rates or use RBRVS-based conversion factors distinct from Medicare. Confirm your state’s Medicaid fee schedule before billing. Blanket statements about universal Medicaid coverage are inaccurate given this state-by-state variation.

Valid modifiers for CPT code 00104

Anesthesia claims require a provider-type modifier on every submission. Missing the modifier is a top denial reason. The correct modifier depends on who administered the anesthesia and whether supervision was involved.

For ECT specifically, QS (MAC) is the most frequently used modifier because monitored anesthesia care with propofol or methohexital is the standard approach. Apply AA or QS together when an anesthesiologist personally performs MAC. Always check payer-specific policies: some commercial insurers have additional modifier requirements beyond the standard CMS set.

ICD-10 codes used with CPT 00104

Every CPT 00104 claim requires a paired ICD-10 diagnosis code establishing medical necessity. The diagnosis code comes from the treating psychiatrist’s record, not the anesthesiologist’s own assessment. Mismatched or missing ICD-10 codes, such as a stale F33.3 entry that no longer matches the psychiatrist’s current diagnosis, are a primary denial trigger. Commonly paired codes include:

For a complete crosswalk of ICD-10 codes pairable with CPT 00104, use the AAPC Codify CPT lookup, which displays linked diagnosis codes alongside each procedure code. Confirm that the diagnosis on the anesthesia claim matches the primary diagnosis on the psychiatrist’s contemporaneous notes.

CPT 90870 vs CPT 00104: Who bills what?

One of the most common ECT billing questions is whether the psychiatrist or anesthesiologist bills 00104. The answer is always the anesthesia provider. The psychiatrist bills CPT 90870 for administering the ECT itself. Both codes are reported on the same date of service but by different providers on separate claims.

A psychiatric practice running ECT in-house should confirm that their billing workflows clearly separate the psychiatrist’s 90870 claim from the anesthesia provider’s 00104 claim. Submitting both under a single National Provider Identifier (NPI) is a compliance risk and an automatic denial in most payer systems.

Add-on code CPT 99100: Qualifying circumstances

CPT 99100 is a qualifying circumstance add-on code that may be reported alongside 00104 when anesthesia is provided under conditions that significantly affect the character of the service. The qualifying circumstance under 99100 is the patient’s age, not a psychiatric diagnosis – so it only applies to a small share of ECT cases.

CPT 99100 descriptor: Anesthesia for patient of extreme age, younger than 1 year and older than 70. There is no severe-psychiatric-disease criterion under this code – a patient’s psychiatric severity is instead reflected through the ASA physical-status P-modifiers on the anesthesia claim, not through 99100.

Since ECT is typically performed on adults well within that 1-to-70 age range, 99100 applies to relatively few ECT cases. Where it does apply, it’s reported as a separate line on the same claim, not as a modifier, and it carries a unit value of 1.

Medicare assigns CPT 99100, along with the rest of the 99100-99140 qualifying-circumstances family, a national status indicator of B (bundled) – its value is folded into the primary anesthesia code’s RVUs, and it isn’t paid as a separate line regardless of documentation.

Some commercial payers follow the same bundling approach, though policies vary, so verify the specific payer contract. See Pabau’s CPT 99100 guide for full context on the 99100-99140 add-on family.

Simplify ECT anesthesia billing with Pabau

Practice management software like Pabau keeps ECT documentation and billing in one place – from psychiatry EMR notes through claims submission – with field validation before submission, so your anesthesia billing team works from one complete, shared patient record.

Book a demo

Documentation requirements for ECT anesthesia claims

A clean CPT 00104 claim depends entirely on the quality of the anesthesia record. Missing or vague documentation is the second most common reason for denial after modifier errors. Every ECT anesthesia record should include the following elements to support HIPAA compliance for medical offices and payer audit requirements:

• Pre-anesthesia evaluation: Patient history, ASA physical status classification, airway assessment, allergies, and informed consent
• Anesthesia start and stop times: Exact clock times for induction and recovery handoff; these determine your time unit calculation
• Anesthesia technique: Documentation that general anesthesia or MAC was used, with agents and dosages recorded
• Monitoring record: Continuous vital signs (BP, HR, SpO2, EtCO2 if applicable) throughout the procedure
• Post-anesthesia evaluation: Patient assessment before handoff to recovery; Modified Aldrete or Steward recovery score recommended
• Attestation for medical direction: If QK modifier is used, the seven TEFRA medical direction requirements must each be documented

Strong patient care management practices mean documentation is completed at point of care, not reconstructed later. Retrospective documentation is a red flag in Medicare audits and significantly increases denial risk. Use digital intake forms to standardize the pre-anesthesia checklist and ensure every required field is captured before the patient enters the procedure room.

Common billing errors and how to avoid them

ECT anesthesia claims have a predictable set of denial patterns. Most are preventable with a pre-submission checklist. Moving to paperless clinical documentation reduces the manual transcription errors that drive several of these issues.

• Missing or incorrect modifier: Submitting CPT 00104 without an anesthesia provider modifier (AA, QS, QK, etc.) is the single highest-volume denial reason. Every claim needs a modifier.
• Mismatched ICD-10 code: Using a diagnosis code that is not on the payer’s LCD crosswalk for ECT. Confirm the ICD-10 code from the psychiatrist’s record matches a covered diagnosis before submission.
• Incorrect time unit calculation: Rounding time up rather than down, or using 10-minute increments when the payer uses 15-minute increments. Document exact anesthesia times and calculate units correctly per payer contract.
• Dual-provider billing error: A practice billing both CPT 90870 and CPT 00104 under the same NPI. These two codes belong to different providers on separate claims.
• Misreporting the CPT 99100 add-on: Applying 99100 for psychiatric severity rather than the actual qualifying circumstance (patient younger than 1 or older than 70), or billing it as a separate payable line to Medicare, which bundles 99100 into 00104’s RVUs (CMS status indicator B) and won’t pay it separately. Confirm the qualifying circumstance and payer bundling policy before reporting it.
• Failure to obtain prior authorization: Some Medicare Advantage and commercial plans require prior authorization for ECT series. Submitting without auth triggers an automatic denial.

How practice management software supports ECT anesthesia billing

Anesthesia billing for ECT is operationally demanding. Each session involves precise time tracking, strict modifier requirements, and coordination between two separate billing providers. Manual workflows are where these requirements get missed, generating denials.

Pabau’s claims management software validates required fields before a claim is submitted, so missing or incorrect entries get flagged at the point of entry rather than after a denial arrives.

For psychiatric practices managing ECT in-house, psychiatry EMR software from Pabau keeps the anesthesiologist’s and psychiatrist’s ECT documentation in the same patient record, so the anesthesia biller can reference the psychiatrist’s diagnosis code directly instead of chasing it down separately.

Keeping the treating psychiatrist’s diagnosis codes in the same record as the anesthesia claim means the biller can reference them directly instead of requesting them from a separate provider. For practices managing multiple ECT patients across recurring sessions, practice management software that tracks anesthesia time documentation against claim submission history also supports audit readiness.

Conclusion

CPT code 00104 is a technically specific billing code. The core risks, missing modifiers, incorrect provider assignment, and undocumented anesthesia times, are all preventable with structured pre-submission workflows.

Practice management software like Pabau keeps ECT documentation and billing tied to one patient record – from psychiatry EMR notes through claims submission – with field validation before a claim leaves the practice. To see how this works for your anesthesia or psychiatric practice, book a demo.

Continue your research

Managing psychiatric billing across multiple providers? Psychiatry EMR software from Pabau connects the treating clinician’s record with the billing workflow, so every provider on the account can reference the same diagnosis code directly instead of requesting it separately.

Need to document ECT treatment consent and pre-procedure assessments? Digital intake forms let you build standardized anesthesia pre-assessment checklists that populate directly into the patient record.

Want a structured overview of mental health billing requirements? H0036 covers community psychiatric supportive treatment billing and shares many of the same documentation principles as ECT anesthesia billing, including diagnosis specificity and medical necessity documentation.

Frequently asked questions