CPT Code 00104: Anesthesia for Electroconvulsive Therapy – Complete Billing & Coding Guide

CPT code 00104 describes anesthesia services provided during electroconvulsive therapy (ECT), a psychiatric procedure in which controlled electrical stimulation induces a brief seizure under general anesthesia to treat severe, treatment-resistant mental health conditions. This code is the designated anesthesia crosswalk for the ECT procedure code CPT 90870, though its separate billability is one of the most misunderstood and payer-variable questions in behavioral health coding. Understanding exactly when 00104 can — and cannot — be reported independently is essential for anesthesia billing teams, psychiatric practices, and revenue cycle professionals managing ECT claims.

What Does CPT Code 00104 Mean?

CPT 00104 is classified within the AMA CPT code set’s Anesthesia section under “Anesthesia for Procedures on the Head.” Its official descriptor is: Anesthesia for electroconvulsive therapy.

Key attributes of this code at a glance:

• Billable status: Active and valid for CY 2025 with no descriptor changes
• Service category: Anesthesia (CPT range 00100–01999)
• Applicable setting: Inpatient hospital, outpatient hospital/ASC, or designated ECT treatment suite
• Provider type: Anesthesiologist (MD/DO), CRNA, or Anesthesiologist Assistant (AA) — each with required HCPCS modifier
• Payment methodology: Base units + time units × anesthesia conversion factor (not standard RVU formula)
• Time limit (Medicare): Limited to one time unit (15 minutes) per the CMS Medicare Claims Processing Manual

What Services and Procedures Does CPT 00104 Cover?

CPT 00104 captures all anesthetic services inherent to a single ECT session, from the pre-induction preparation through the post-procedure recovery period. The code encompasses:

• Pre-procedure patient assessment and anesthesia plan documentation
• Induction of general anesthesia (most commonly a rapid-acting IV agent such as methohexital or propofol plus a neuromuscular blocking agent)
• Airway management and patient monitoring during the seizure induction phase
• Post-anesthesia monitoring until the patient meets discharge or transfer criteria
• Routine supplies and medications integral to anesthesia administration

What Does CPT 00104 Specifically Exclude?

Coders should not expect 00104 to capture the following — each requires distinct coding or is not separately billable:

• The ECT procedure itself (reported with CPT 90870, Electroconvulsive therapy, including necessary monitoring)
• Cognitive or neuropsychological assessments performed on the same date
• Pre-anesthesia evaluation/consultation billed on a separate, prior date (may be separately reportable with E&M codes)
• Arterial catheter placement (CPT 36620) or other separately billable procedural services not inherent to routine ECT anesthesia
• Anesthesia services when the same psychiatrist who performs ECT also administers anesthesia — this is bundled under Medicare and many commercial payers

When Is CPT 00104 the Right Code to Use?

Selecting 00104 correctly requires more than identifying a procedure crosswalk. A coder or billing team must confirm all of the following conditions are met:

1. Confirm ECT (CPT 90870) was performed — 00104 has no standalone clinical rationale; it is always an adjunct to the underlying psychiatric procedure.
2. Confirm the anesthesia provider is separate from the performing psychiatrist — if the psychiatrist personally administers anesthesia and performs ECT, payers including Medicare bundle all services into 90870.
3. Confirm the payer is not one that auto-bundles 00104 into 90870 — check the applicable LCD, payer policy, or NCCI edit table before submitting 00104 on a professional claim.
4. Confirm an anesthesia provider modifier is appended — claims without modifier AA, QK, QS, QX, QY, or QZ will be denied or returned.
5. For Medicare claims, apply the one-time-unit rule — 00104 is limited to one time unit (15 minutes); report base units only plus the applicable single time unit.
6. Confirm the ICD-10-CM diagnosis code establishes medical necessity — appropriate diagnoses include major depressive disorder (F32.x, F33.x), bipolar disorder with severe features, or treatment-resistant schizophrenia.

How Does CPT 00104 Differ From CPT 90870?

These two codes describe different provider roles within the same clinical encounter and are frequently confused on claims.

What Documentation Is Required to Support CPT 00104?

What Must the Provider Document in the Anesthesia Record?

Documentation for 00104 must support both the medical necessity of anesthesia and the services performed. A complete anesthesia record should include:

1. Pre-anesthesia evaluation note confirming patient assessment and anesthesia plan
2. Documented informed consent for anesthesia
3. ASA Physical Status classification (P1–P6) supported by documented comorbidities
4. Induction agent(s), dosage, and route of administration
5. Neuromuscular blocking agent used (e.g., succinylcholine) and dose
6. Airway management method (mask, LMA, or ET tube if applicable)
7. Continuous physiologic monitoring record (ECG, SpO2, blood pressure, EtCO2)
8. Anesthesia start and end time (critical for time unit calculation)
9. Post-anesthesia care unit (PACU) note or recovery documentation
10. Provider identity and credential (anesthesiologist, CRNA, or AA) and supervising physician if applicable

What Are the Documentation Standards for Facility vs. Non-Facility Settings?

How Does CPT 00104 Affect Medical Billing and Reimbursement?

Anesthesia codes do not follow the standard RVU and reimbursement rates formula used for most physician services. Instead, payment is calculated using:

(Base Units + Time Units) × Anesthesia Conversion Factor = Allowable Amount

CPT 00104 has an ASA base unit value of 4 base units per the ASA Relative Value Guide. Under Medicare, time is limited to one unit (15 minutes), yielding a formula of (4 + 1) × Medicare Conversion Factor.

Note: Actual reimbursement varies by MAC jurisdiction, geographic adjustment (GPCI), and individual payer contract terms. The 2025 Medicare Anesthesia Conversion Factor decreased 2.20% from the 2024 rate of $20.7739, per the American Society of Anesthesiologists.

What Modifiers Are Commonly Used With CPT 00104?

All anesthesia claims for 00104 must include one provider-role modifier (AA, QK, QY, AD, QX, or QZ) in the first modifier position. Claims submitted without this modifier will be returned or denied.

Are There Any Prior Authorization, Coverage Restrictions, or LCD Requirements?

• Medicare bundling rule: Under NCCI edits, 00104 carries a modifier indicator of ‘0’ when paired with 90870 — meaning no modifier can unbundle these codes when billed by the same provider. Medicare will not separately reimburse anesthesia services when the psychiatrist who performs ECT also provides anesthesia; the RVUs for 90870 were increased in 2002 to account for this.
• Independent anesthesia provider exception: When an anesthesiologist or CRNA separate from the ECT physician provides anesthesia, a professional claim for 00104 may be submitted — but payer policy must be verified first.
• Facility bundling (OPPS): Under the Outpatient Prospective Payment System, 00104 and 90870 billed together on the same date of service are grouped into APC 0320. No separate facility payment is made for the anesthesia component.
• Commercial payers (Optum/UnitedHealthcare, BCBS): Most major commercial plans follow the Medicare bundling policy. Some may separately adjudicate 00104 when submitted with modifier AA by an independent anesthesiologist with supporting documentation.
• Prior authorization: Most payers require prior authorization for ECT itself (90870), not specifically for the anesthesia component. Confirm ECT authorization before submitting the anesthesia claim.

What CPT or HCPCS Codes Are Commonly Billed Alongside CPT 00104?

When 00104 is billable at all, it typically appears in the context of the following codes:

Which Code Combinations Trigger NCCI or CCI Edits?

• 00104 + 90870: The highest-risk combination. NCCI bundles 00104 into 90870 with a modifier indicator of ‘0’ — unbundling is not permitted for the same provider.
• 00104 + 00104: Duplicate billing for multiple ECT sessions on the same date is not recognized; only one unit of 00104 is reportable per operative session.
• Note: CPT® Assistant (March 2010) advises that when the psychiatrist also administers anesthesia, 00104 should be separately reported — but this contradicts CCI policy. Coders should confirm each payer’s position before following CPT® Assistant guidance over NCCI edits.

What Coding Errors Should You Avoid With CPT 00104?

In practice, anesthesia billing teams encounter a predictable set of errors with this code. Ranked by audit frequency and claim impact:

1. Billing 00104 by the ECT psychiatrist — the most common error; Medicare and most commercial payers do not separately reimburse anesthesia when the performing psychiatrist also provides it.
2. Omitting the anesthesia provider modifier — all anesthesia claims require an HCPCS modifier (AA, QK, QS, QX, QY, QZ); missing this field triggers automatic denial.
3. Exceeding one time unit on Medicare claims — the CMS Medicare Claims Processing Manual limits 00104 to one time unit (15 minutes); claiming additional time units will be down-coded or denied.
4. Billing 00104 on facility claims expecting separate payment — under OPPS, anesthesia is packaged into the ECT APC; facilities should still report the code on the UB-04 for statistical accuracy, but should not expect separate reimbursement.
5. Failing to verify payer-specific policy before billing — assuming Medicare rules apply universally is a recurring error; some commercial payers do separately reimburse 00104 for independent anesthesiologists.
6. Missing or insufficient ICD-10-CM diagnosis — the procedure must be supported by a diagnosis that establishes medical necessity for ECT (e.g., F32.3 – Major depressive disorder, severe with psychotic features).

What Do Auditors and RAC Reviewers Look for When Reviewing Claims With CPT 00104?

• Presence of a complete, contemporaneous anesthesia record (not reconstructed after the fact)
• Confirmation that the anesthesia provider is a different clinician from the ECT physician (required for separate payment)
• Matching ICD-10-CM code that supports ECT as medically necessary (treatment-resistant condition documentation)
• Correct modifier sequence and provider credential documentation
• Time units claimed vs. documented anesthesia start/end times
• Same-day E&M visits billed by the anesthesiologist — these are rarely appropriate and draw scrutiny

How Does CPT 00104 Relate to Other CPT Codes?

What Is the Correct Code Sequencing When CPT 00104 Appears With Other Codes?

1. Report CPT 90870 as the primary procedure on the psychiatrist’s professional claim (CMS-1500).
2. Report CPT 00104 with the appropriate anesthesia provider modifier on the anesthesiologist’s or CRNA’s separate professional claim.
3. If the patient is over age 70 and anesthesia complexity is increased, add qualifying circumstance code +99100 to the anesthesia claim.
4. If an emergency condition exists, +99140 may be appended with supporting documentation.
5. On facility UB-04 claims (hospital/ASC), report both 90870 and 00104 with appropriate revenue codes, understanding that under OPPS, only the APC-based composite payment will be issued.

Real-World Coding Scenario — How CPT 00104 Is Applied in Practice

A 74-year-old patient with severe, treatment-resistant major depressive disorder (F33.2) is admitted for an acute ECT course. The treating psychiatrist (Dr. A) performs ECT and monitors the patient throughout. A separate anesthesiologist (Dr. B) provides general anesthesia from induction through recovery. The session lasts approximately 25 minutes of total anesthesia time. Dr. A’s group and Dr. B’s anesthesia group are separate billing entities.

Correct Code Application

• Dr. A’s claim: CPT 90870 with ICD-10-CM F33.2 — one unit, no anesthesia code
• Dr. B’s claim: CPT 00104 + modifier AA + ICD-10-CM F33.2; add +99100 for patient age >70
  • Medicare payment: (4 base units + 1 time unit + 1 qualifying circumstance unit) × $20.3178 = ~$121.91
• Anesthesia record documents start time, end time, agents used, monitoring data, and recovery note

Common Mistake in This Scenario

• Incorrect: Dr. A’s billing team also submits CPT 00104 on the psychiatrist’s claim alongside 90870, expecting additional reimbursement for the anesthesia component
  • Why it fails: NCCI edits bundle 00104 into 90870 when billed by the same provider group; the claim will be denied or down-coded, and repeated submission may trigger a compliance audit
• Incorrect: Dr. B’s team submits 00104 without any anesthesia provider modifier
  • Why it fails: All anesthesia claims require modifier AA, QK, QY, or another role-defining HCPCS modifier; the claim will reject at the clearinghouse or payer level

Frequently Asked Questions About CPT Code 00104

Is CPT Code 00104 Still Valid for Use in 2025?

CPT code 00104 remains a valid, active anesthesia code for calendar year 2025 with no changes to its official descriptor or base unit assignment. Coders should verify annually against the AMA CPT Professional Edition and the CMS Anesthesiologists Center fee schedule updates to confirm that base unit values and conversion factors are current for the applicable date of service.

Can the Psychiatrist Who Performs ECT Also Bill CPT 00104?

No — under Medicare and most commercial payer policies, a psychiatrist who both performs electroconvulsive therapy (CPT 90870) and administers the anesthesia cannot separately bill CPT 00104. The RVUs assigned to CPT 90870 were increased by CMS to include anesthesia when the performing physician also provides it. Separate reimbursement for 00104 is only available when an independent anesthesiologist, CRNA, or AA is the designated anesthesia provider.

How Is Reimbursement for CPT 00104 Calculated?

Reimbursement for CPT 00104 follows the standard anesthesia payment formula: (Base Units + Time Units) × Anesthesia Conversion Factor. The code carries 4 ASA base units; under Medicare, time is capped at one unit (15 minutes). With the 2025 Medicare Anesthesia Conversion Factor of $20.3178, the estimated Medicare allowable before geographic adjustment is approximately $101.59. Commercial payers use their own contracted conversion factors, which typically range significantly higher than Medicare rates.

What Is the Difference Between NCCI Edits and CPT® Assistant Guidance on CPT 00104 and 90870?

This is one of the most practically important distinctions in ECT billing. The CMS National Correct Coding Initiative (NCCI) bundles 00104 into 90870 with a modifier indicator of ‘0,’ meaning these codes cannot be separately reported for the same provider under any circumstance. However, CPT® Assistant (March 2010 edition) states that when a psychiatrist administers anesthesia for ECT, 00104 should be separately reported. These two authoritative sources conflict directly. Because NCCI edits govern Medicare adjudication, the CCI rule controls for Medicare claims; for commercial payers not bound by NCCI, the CPT® Assistant guidance may apply — but must be confirmed with each payer.

What Modifiers Are Required When Billing CPT 00104?

All claims for CPT 00104 must include an anesthesia provider modifier in the first modifier position. Physician anesthesiologists report AA (personal performance), QK (medical direction of 2–4 CRNAs), QY (direction of one CRNA), or AD (supervision of more than 4 concurrent procedures). CRNAs report QX (with physician direction) or QZ (without physician direction). MAC-level services are indicated with modifier QS, which may be used by both physicians and CRNAs. Claims missing this modifier will be denied.

Does CPT 00104 Require a Separate Prior Authorization?

Prior authorization for CPT 00104 specifically is rarely required by payers. Authorization requirements typically apply to the ECT procedure itself (CPT 90870), with the anesthesia component considered part of the authorized service. However, billing teams should confirm that the ECT authorization explicitly covers associated anesthesia services, particularly with behavioral health managed care plans and carve-out payers who may apply different rules to the professional anesthesia claim.

Key Takeaways for Billing and Coding CPT 00104

• CPT 00104 describes anesthesia services during ECT and crosswalks to CPT 90870, but is not automatically separately billable — payer policy must be verified first.
• Medicare bundles 00104 into 90870 via NCCI edits; the same provider cannot bill both codes, and no modifier overrides this restriction.
• Independent anesthesiologists or CRNAs billing 00104 on a separate professional claim must include a required HCPCS anesthesia provider modifier (AA, QK, QY, QX, or QZ) or the claim will deny.
• Medicare limits CPT 00104 to one time unit (15 minutes); commercial payers may allow actual documented time but this must be confirmed per contract.
• Qualifying circumstance add-on codes (+99100 for patients over age 70, +99140 for emergency conditions) may be appended to increase base unit value when clinically appropriate.
• The conflict between CPT® Assistant guidance and NCCI edit policy is a genuine ambiguity — coders should not assume CPT® Assistant advice overrides CCI edits for Medicare claims.
• For anesthesia coding audit preparation, complete contemporaneous anesthesia records, matching ICD-10-CM codes, and documented provider separation are the three highest-risk documentation gaps.

For current base unit values and anesthesia conversion factors, refer to the CMS Anesthesiologists Center and the CMS NCCI Policy Manual, Chapter 2.