CPT code 00404: Anesthesia for radical mastectomy procedures

Key Takeaways

CPT code 00404 describes anesthesia for radical or modified radical procedures on the breast and integumentary system on the extremities, anterior trunk, and perineum.

00404 carries 5 base units per the ASA Relative Value Guide; total billed units equal base units plus time units (one unit per 15 minutes of anesthesia care).

Common modifiers include AA (anesthesiologist personally performed), QK (medically directed two to four concurrent cases), and QZ (CRNA without medical direction); incorrect modifier use is the most frequent denial trigger.

Practice management software like Pabau helps surgical practices track anesthesia procedure codes, attach correct modifiers, and reduce claim rejections before submission.

CPT code 00404 is the anesthesia code for radical or modified radical procedures on the breast, reported when an anesthesiologist or CRNA provides anesthesia during a radical or modified radical mastectomy. Getting it right starts with understanding exactly what the code covers and how to calculate the billable units, covered in full below.

This reference covers the official AMA description, base unit calculation, modifier guidance, current reimbursement considerations, ICD-10 crosswalk, related codes in the 00400 series, and common billing errors for CPT code 00404.

CPT code 00404: definition and clinical description

CPT code 00404 describes anesthesia services for procedures on the integumentary system on the extremities, anterior trunk, and perineum, specifically for radical or modified radical procedures on the breast. The American Medical Association (AMA), which maintains the CPT code set, places 00404 in the anesthesia section under codes for the integumentary system, the same category tracked by dermatology EMR software.

The lay description: a patient undergoing a radical or modified radical mastectomy receives general anesthesia before the surgical team removes breast tissue, lymph nodes, and in radical cases the pectoral muscles. The anesthesiologist monitors and manages the patient throughout the procedure. CPT code 00404 captures the anesthesia component of that encounter.

Procedures covered by CPT code 00404

The code’s scope extends across radical and modified radical procedures on the breast. Coders working with plastic surgery EMR software encounter 00404 most often alongside these surgical procedures:

• Radical mastectomy: removes breast tissue, skin, both pectoral muscles, and axillary lymph nodes (Halsted procedure)
• Modified radical mastectomy: removes breast tissue, skin, and axillary lymph nodes while preserving the pectoral muscles (most common mastectomy type billed under 00404)
• Extended radical mastectomy: includes internal mammary lymph node dissection in addition to standard radical mastectomy components
• Skin-sparing mastectomy with reconstruction: when the reconstruction is performed simultaneously and qualifies as a radical/modified radical procedure

The code parent category also covers integumentary procedures on the extremities, anterior trunk, and perineum more broadly, but the primary clinical context for 00404 in practice is breast cancer surgery. Breast-conserving procedures (lumpectomy, partial mastectomy) billed under CPT 19301-19302 typically use different anesthesia codes from the 00400 series, so confirming the surgical CPT before selecting the anesthesia code is essential.

CPT code 00404 base units and time unit calculation

CPT code 00404 carries 5 base units per the AAPC CPT code reference and the ASA Relative Value Guide (RVG). Base units reflect the inherent complexity and risk of anesthesia for the procedure type and do not change based on actual case duration.

Total anesthesia billing units use the standard formula: Total Units = Base Units + Time Units + Qualifying Circumstance Units (if applicable). Time is measured in 15-minute increments, so a 90-minute case contributes 6 time units. A 5-base-unit code for a 90-minute procedure therefore bills at 11 units before any qualifying circumstances.

Some payers require the anesthesia start and stop times to appear on the claim form in Box 24G or an equivalent field. Missing time documentation is one of the most common reasons 00404 claims are held for additional information rather than processed on first pass.

Similar documentation expectations apply to other anesthesia CPT codes, such as 00220 and 00474, across surgical specialties.

Reimbursement and fee schedule for CPT code 00404

Anesthesia reimbursement under Medicare uses a conversion factor multiplied by total billed units, not the standard Relative Value Unit (RVU) framework applied to most physician services. That applies across the whole 00100-01999 anesthesia range, including 00938. RVU lookup tools, including the CMS Physician Fee Schedule search, don’t surface anesthesia base units or conversion factors, because anesthesia codes aren’t RVU-priced.

For the correct figure, use the CMS Anesthesiologists Center, which publishes the anesthesia conversion factors addendum alongside the annual Physician Fee Schedule final rule, or the ASA Relative Value Guide referenced above. Rates vary by Medicare Administrative Contractor (MAC) region, so a practice in New York will see different rates from one in rural Texas.

Because conversion factor amounts change annually and differ by locality, specific dollar figures aren’t stated here. Consult the CMS Anesthesiologists Center directly for current, location-specific reimbursement data. Ensuring HIPAA-compliant practice management software handles claim submission correctly is equally important, since improper claim formatting can delay payment regardless of how accurately the code is selected.

Modifiers for CPT code 00404

Modifier selection for CPT code 00404 determines whether the claim pays correctly or triggers a denial. Anesthesia modifiers communicate who provided the service and under what supervisory arrangement. Attaching no modifier, or the wrong modifier, is one of the most common billing errors on 00404 claims.

When billing under the medical direction model (QK + QX pair), both the anesthesiologist and the CRNA must each submit their respective modifier on the claim. Missing one half of the pair is a common reason medical direction claims are denied or downgraded to the supervision rate.

Claims management software that flags missing modifier pairs before submission catches this before it turns into a denial.

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ICD-10 codes commonly used with CPT 00404

Medical necessity for anesthesia is established through the ICD-10-CM diagnosis code on the claim. For CPT code 00404, the diagnosis code should reflect the condition requiring the surgical procedure, not the anesthesia service itself. Accurate diagnosis coding, such as C50.411, on surgical claims is required to demonstrate medical necessity to payers.

Always code to the highest level of specificity. Use laterality (right vs. left), histology type when documented, and secondary codes for hormone receptor status or genetic predisposition when they influence the medical decision-making. Practices should also confirm whether Z85.3 applies to follow-up or prophylactic procedures, since a personal history code changes the medical necessity picture from an active malignancy diagnosis.

Related anesthesia CPT codes in the 00400 series

The 00400 family covers anesthesia for integumentary procedures across the extremities, anterior trunk, and perineum. Selecting the wrong sibling code, such as confusing 00404 with 00410, is a common crosswalk error. The table below clarifies when each code applies versus CPT code 00404.

The most frequent selection error is billing 00402 instead of 00404 when a reconstructive procedure follows a mastectomy in the same operative session. When reconstruction immediately follows the radical procedure, 00404 remains the correct anesthesia code for the primary procedure, and any additional anesthesia time for reconstruction should be documented in the same claim rather than split under 00402.

Coding tips and common billing errors for CPT code 00404

Most 00404 denials trace back to four documentation and coding problems. Identifying these before submission saves the resubmission cycle entirely. Practices that standardize their pre-submission workflow using digital intake forms and structured documentation templates reduce the likelihood of missing anesthesia record details that payers require.

• Missing or incorrect modifier: No modifier on an anesthesia claim is an automatic technical denial with most Medicare MACs. Confirm the care model (AA, QK/QX, QZ) before submission and ensure both sides of a medical direction pair are on file.
• Underdocumented anesthesia time: Payers need a continuous anesthesia time record with start and stop times. Missing entries in the intraoperative record or missing pre-induction and emergence documentation lead to requests for medical records that delay payment.
• Wrong code for the procedure type: Billing 00402 (reconstructive) for a radical mastectomy or 00406 (with internal mammary node dissection) when that element was not performed are the two most frequent procedure-to-code mismatches in this family.
• Qualifying circumstances reported without payer verification: Add-on codes 99100 (extreme age), 99116 (total body hypothermia), and 99135 (controlled hypotension) increase billed units but not all commercial payers accept them alongside 00404. Verify payer policy before reporting.
• Laterality missing from ICD-10 code: Using an unspecified breast code (C50.919) when the operative note documents a specific side leads to data quality flags with some Medicare auditors.

The same documentation-specificity principle applies when distinguishing 00404 from a closely related sibling like 00400: the more precisely the anesthesia record matches the claim data, the fewer information requests arrive from the MAC.

For guidance on HIPAA compliance for medical offices, particularly around how anesthesia records must be stored and transmitted securely, practices should review their documentation workflows against current HIPAA Security Rule requirements. HIPAA mandates use of standardized CPT codes in all electronic claims transactions.

Conclusion

Anesthesia billing for radical breast surgery is precise work. CPT code 00404 carries 5 base units, requires the correct anesthesia modifier to reflect who performed and supervised the service, and depends on specific ICD-10 diagnosis codes to establish medical necessity.

The most preventable errors, wrong modifier, missing time documentation, and procedure-code mismatches with the 00402 or 00406 sibling codes, all stem from incomplete documentation rather than unfamiliarity with the codes themselves.

Pabau’s practice management software helps surgical practices structure their pre-submission workflow so anesthesia claim data is complete before it reaches the clearinghouse. To see how it handles procedure code tracking and modifier validation, book a demo.

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