CPT® Code 01400

Quick Reference

• Code definition: CPT 01400 covers anesthesia for open or surgical arthroscopic procedures on the knee joint when no more specific knee anesthesia code (01402 for TKA, 01404 for disarticulation) applies. It is the NOS catch-all for the majority of knee surgeries, including meniscectomy, ACL reconstruction, osteotomy, chondroplasty, and synovectomy.
• Key billing rule: Anesthesia payment uses the formula (Base Units + Time Units + Qualifying Circumstance Units) × Conversion Factor. Unlike surgical codes, there are no RVUs; time reporting is central to correct payment. CMS and most payers use 1 time unit per 15 minutes; verify by contract.
• Modifier essentials: Every anesthesia claim requires two modifier types: a provider/medical direction modifier (AA, QK, QX, QY, QZ, or QS) and a physical status modifier (P1 through P6). Omitting either triggers denial. The QK/QX pair is required when an anesthesiologist medically directs 2 to 4 concurrent cases.
• Documentation must-have: Anesthesia start and stop times, recorded in the anesthesia record and consistent across the OR record, nursing notes, and surgeon's operative note. Time discrepancies across records are the leading audit trigger for anesthesia claims.
• Top confusion point: Billing 01400 NOS for total knee arthroplasty (CPT 27447) is incorrect. TKA requires 01402, which carries higher base units. This error results in systematic underpayment and will not trigger denial, making it easy to miss.
• Payer alert: In the hospital outpatient setting, 01400 is packaged into APC rates; the facility does not separately bill anesthesia. The anesthesiologist still bills Medicare Part B on a separate CMS-1500. Do not confuse facility billing with the professional anesthesia claim.

When to Use This Code

CPT 01400 applies whenever an anesthesiologist (or CRNA) provides anesthesia for an open or surgically arthroscopic knee procedure and neither of the two more specific codes in the 01400 series is appropriate. The broad scope of this code covers the majority of knee surgeries performed in ambulatory surgery centers and hospital ORs:

• Surgical arthroscopy: meniscectomy, meniscal repair, ACL and PCL reconstruction, chondroplasty, osteochondral allograft, loose body removal, synovectomy
• Open knee procedures not classified as TKA or disarticulation: osteotomy, tibial tubercle transfer, patellofemoral realignment, open synovectomy, unicondylar arthroplasty
• Diagnostic arthroscopy under general or regional anesthesia (CPT 29870)

What falls outside 01400:

• Total knee arthroplasty (CPT 27447, 27487): use 01402
• Knee disarticulation or amputation: use 01404
• Closed (non-incisional) knee procedures, including manipulation under anesthesia (MUA), aspiration under anesthesia, and closed fracture reduction: use 01380
• Procedures on the upper ends of tibia, fibula, or patella via closed approach: use 01390

Provider and setting context: 01400 is reported on the anesthesiologist's or CRNA's claim, never on the surgeon's claim. The surgical procedure code (e.g., 29881) belongs to the surgeon. CMS assigns TOS 7 (Anesthesia) and BETOS P0 (Anesthesia) to this code, confirming its exclusive use for the anesthesia service.

Timed code mechanics: Anesthesia time begins when the anesthesiologist starts preparing the patient for induction (not incision) and ends when the anesthesiologist is no longer in personal attendance. Document in minutes; CMS converts to time units at 15 minutes per unit. For a 60-minute case: 3 base units + 4 time units = 7 total units before qualifying circumstances. Verify whether your commercial contract uses 10-minute or 15-minute increments, as this materially affects reimbursement.

Code Differentiation Table

The most consequential differentiation is 01400 vs. 01402. Because 01402 carries more base units (7 vs. 3 for 01400 per ASA RVG training standards), miscoding TKA cases as 01400 creates systematic underpayment that may not generate denials. Review the surgeon's operative note to confirm whether the procedure is a TKA before defaulting to 01400 NOS.

Billing and Modifier Rules

Provider and Medical Direction Modifiers

CMS requires a provider type modifier on every anesthesia claim. Select the modifier that accurately reflects the actual supervision arrangement on the date of service [1]:

Payment is reduced proportionally as supervision intensity decreases. AA pays 100% of allowed units; QK direction cases pay 50% per case to the anesthesiologist. AD supervision (more than 4 concurrent) triggers further reduction.

Physical Status Modifiers

Append a physical status modifier to 01400 on every claim. The ASA Relative Value Guide assigns additional base units for higher-acuity status: P3 adds 1 unit, P4 adds 2 units, P5 adds 3 units [2]. Document clinical support for any classification above P2 in the pre-anesthesia evaluation.

Qualifying Circumstance Add-On Codes

Report these separately in addition to 01400 when applicable:

• 99100: Patient under age 1 or over age 70. Adds 1 qualifying circumstance unit. This is the most frequently applicable add-on for Medicare knee cases.
• 99135: Controlled hypotension utilized. Adds 5 units. Document the technique and MAP target in the anesthesia record.
• 99140: Emergency conditions. Adds 2 units. Document why delay would increase risk to life or body part.
• 99116: Total body hypothermia. Rare for knee surgery but includable when applicable.

Add-On Code 0887T

CPT 0887T (end-tidal control of inhaled anesthetic agents and oxygen) is an add-on code reportable with 01400 per CPT guidelines when this technology is used to assist anesthesia delivery. List separately; do not report as a standalone code.

Bundling

01400 bundles the following services; do not separately bill [3]:

• Routine monitoring (pulse oximetry, ECG, non-invasive blood pressure, temperature)
• Anesthesia agent administration
• Peripheral IV placement
• Pre- and post-anesthesia evaluation and care
• Endotracheal intubation as part of the anesthetic

Separately reportable with supporting documentation: Arterial line placement (36620), central venous catheter placement (36556, 36557), and pulmonary artery catheter (93503) when medically necessary for the patient's condition. Nerve blocks performed exclusively for postoperative pain management (femoral nerve block 64447, adductor canal block 64415) may be separately billable when documented as a distinct service from the primary anesthetic. If the nerve block is the primary anesthetic technique, bill 01400 only.

MUE for 01400 is listed as "not applicable/unspecified," consistent with time-based anesthesia billing where payment is driven by reported time units rather than a unit cap.

Bilateral Surgery

The bilateral surgery modifier (50) does not apply to anesthesia codes. CMS confirms the concept does not apply to 01400. For simultaneous bilateral knee procedures, report one anesthesia code with the total anesthesia time for the combined case and verify payer-specific instructions.

Documentation Essentials

The anesthesia record must contain [1]:

• Times: Anesthesia start time and end time, expressed in clock time and convertible to total minutes. These must match the OR time-out record, nursing documentation, and surgeon's operative note.
• Anesthesia type: General (ETT or LMA), neuraxial (spinal or epidural), regional, or MAC. This determines whether QS applies.
• Physical status: P1 through P6 classification with clinical justification documented in the pre-anesthesia evaluation.
• Personnel present: Identifies which modifier (AA, QK, QX, QY, QZ) is correct. If QK is claimed, the record must show the anesthesiologist was not personally performing one of the concurrent cases.
• Qualifying circumstances: Age verified from the medical record for 99100; description of emergency condition for 99140; documented MAP reduction for 99135.
• Post-anesthesia evaluation: Required by CMS and ASA guidelines.

For medical direction claims (QK, QX, QY), CMS requires documentation of all seven medical direction activities [1]:

1. Pre-anesthetic examination and evaluation performed
2. Anesthesia plan prescribed
3. Personal participation in the most demanding aspects of induction and emergence
4. Verification the CRNA/AA is not concurrently supervising another case
5. Monitoring at frequent intervals
6. Physical presence available for immediate diagnosis and treatment
7. Post-anesthesia care provided

Failure to document all seven activities in the medical record is the primary audit finding in RAC and OIG reviews targeting anesthesia medical direction claims.

Audit red flags specific to 01400:

• Anesthesia time that does not reconcile across OR, PACU, and anesthesia records
• Physical status P3 or P4 without clinical findings in the pre-anesthesia evaluation
• 99100 billed without the patient's verified date of birth confirming age eligibility
• QK claimed when the anesthesiologist was performing another case as the primary provider (making concurrent direction impossible)

Medicare, Commercial, and Medicaid Payer Rules

Medicare

Medicare Part B covers anesthesia services by a physician anesthesiologist, CRNA, or anesthesiologist assistant (AA) for covered surgical procedures [1]. No National Coverage Determination exists specifically for anesthesia for knee surgery; coverage follows the underlying surgical procedure. If the knee surgery meets medical necessity, the anesthesia service is covered.

The global surgery package does not extend to the anesthesiologist. The surgeon's 90-day global period for CPT 27447 or 29881 does not affect anesthesia billing. The anesthesiologist bills separately on the date of service regardless of the surgical global.

The anesthesia conversion factor is updated annually in the CMS Physician Fee Schedule Final Rule published each November [4]. Verify the current-year conversion factor before calculating expected reimbursement.

In the hospital outpatient setting, 01400 carries an APC status of "Items and Services Packaged into APC Rates." The facility does not bill separately for anesthesia; it is packaged into the procedure's APC payment. The professional anesthesia claim to Medicare Part B is unaffected.

Commercial Payers

Most commercial contracts base anesthesia payment on the same base unit plus time unit formula as Medicare, but the conversion factor, time unit interval (10 or 15 minutes), and physical status unit values may differ. Verify each payer contract individually. Some commercial payers apply automated claim edits that downcode 01400 to 01380 for outpatient arthroscopic cases based on coding pattern flags; submit operative report documentation proactively when patterns show automated downcoding.

CRNA Opt-Out States

For QZ billing (CRNA without physician direction), the state must have opted out of Medicare's physician supervision requirement. CRNAs billing QZ in non-opt-out states create a compliance exposure even if the state practice act permits independent CRNA practice; facility and payer requirements govern Medicare billing, not state scope of practice statutes alone.

Common Denials and Prevention

Missing provider type modifier The claim line lacks AA, QK, QX, QY, QZ, or QS. CMS processing systems require this modifier on every anesthesia claim. Prevention: build a claim edit in the billing system that flags any 01400 claim without a provider type modifier before submission.

Physical status modifier absent or unsupported Claim submitted without a P modifier, or P3 or P4 assigned without clinical documentation. Auditors request pre-anesthesia evaluation notes and look for objective findings supporting the classification. Prevention: pre-anesthesia evaluation templates should prompt anesthesiologists to record the specific conditions supporting ASA physical status assignment.

Time discrepancy across records Anesthesia start or stop time on the claim does not match the OR record or PACU record, triggering a request for records and potential overpayment demand. Prevention: implement a closing-of-record process where the anesthesiologist reconciles times before signing the anesthesia note.

01400 used instead of 01402 for TKA Because this is an underpayment rather than an overpayment, it will not generate a denial but surfaces in payment integrity reviews or internal audits. Prevention: link the anesthesia code selection to the surgical CPT code at charge entry; if the surgeon bills 27447, the anesthesia charge should trigger a validation prompt for 01402.

99100 billed without age verification The qualifying circumstance is reported, but the patient's date of birth in the record does not support age under 1 or over 70. Prevention: automate age verification from the patient demographic record before applying 99100 at charge capture.

Coding Scenarios

Scenario 1: Arthroscopic meniscectomy, anesthesiologist personally performing

A 35-year-old male with a medial meniscus tear undergoes arthroscopic medial meniscectomy (CPT 29881) in an ASC under general anesthesia. The anesthesiologist is the sole provider. Anesthesia time is 45 minutes.

Correct coding: 01400-AA-P1

Why: 01400 NOS applies to surgical arthroscopic knee procedures. 99100 does not apply; the patient is 35. The anesthesiologist is personally performing, so AA is correct. Claim units: 3 base + 3 time (45 min / 15) = 6 units.

Scenario 2: ACL reconstruction, CRNA under medical direction

A 22-year-old male athlete undergoes arthroscopic ACL reconstruction. The anesthesiologist is concurrently medically directing two additional OR cases. The CRNA administers general anesthesia. Anesthesia time is 105 minutes.

Correct coding: Anesthesiologist claim: 01400-QK-P1. CRNA claim: 01400-QX-P1.

Why: Medical direction of 2 to 4 concurrent cases requires the QK/QX pair. Both claims are required. The anesthesiologist receives 50% of allowed units per direction case. 99100 is not applicable for this patient's age.

Scenario 3: Emergency tibial plateau ORIF with controlled hypotension, trauma patient

A 55-year-old male presents with an open tibial plateau fracture. The surgeon performs open reduction internal fixation (ORIF) on an urgent basis. The anesthesiologist personally provides general anesthesia with deliberate controlled hypotension to minimize intraoperative blood loss, achieving a mean arterial pressure reduction of more than 30%. Anesthesia time is 180 minutes.

Correct coding: 01400-AA-P3 + 99140 + 99135

Why: 99140 requires documented emergency conditions; the open fracture with risk of compartment syndrome and hemorrhage supports this. 99135 requires documented controlled hypotension technique with MAP reduction of 30% or greater. P3 is appropriate for acute traumatic injury with systemic physiologic compromise. Verify the specific anesthesia code against the anatomic classification of the procedure; if the surgical code maps to the knee joint, 01400 applies.

Scenario 4: Bilateral simultaneous TKA, patient age 72 with diabetes

A 72-year-old female with insulin-dependent type 2 diabetes undergoes bilateral simultaneous TKA. The anesthesiologist personally administers spinal anesthesia. Total anesthesia time is 240 minutes.

Correct coding: 01402-AA-P3 + 99100

Why: Bilateral simultaneous TKA is still TKA; use 01402, not 01400. The bilateral surgery modifier (50) does not apply to anesthesia codes. One anesthesia code is reported with the total case time. 99100 applies because the patient is over 70. P3 reflects insulin-dependent diabetes with systemic implications; document clinical findings supporting P3 in the pre-anesthesia evaluation.

Related Codes

• 01380: Anesthesia, all closed procedures on knee joint. Use for MUA, aspiration under anesthesia, and closed fracture reduction.
• 01390: Anesthesia, closed procedures, upper ends of tibia, fibula, and/or patella. Use for closed procedures at proximal tibia/fibula or patella.
• 01402: Anesthesia, total knee arthroplasty. Required specifically for TKA; carries higher base units than 01400.
• 01404: Anesthesia, disarticulation at knee. Use for knee disarticulation procedures.
• 99100: Qualifying circumstance, extreme age (under 1, over 70). Commonly paired add-on for Medicare knee surgery patients.
• 99135: Qualifying circumstance, controlled hypotension. Add-on when deliberate hypotension technique is used.
• 99140: Qualifying circumstance, emergency conditions. Add-on for urgent/emergent knee procedures.
• 0887T: End-tidal control of inhaled anesthetic agents and oxygen. Add-on reportable in conjunction with 01400 per CPT guidelines.
• 29881: Arthroscopy, knee, surgical; with meniscectomy. Common surgical procedure paired with 01400 on the surgeon's claim.
• 27447: Total knee arthroplasty. Paired with 01402 (not 01400) on the anesthesiologist's claim.

Sources

1. CMS Medicare Claims Processing Manual, Chapter 12 — CMS anesthesia billing rules, medical direction requirements, seven required activities, time reporting standards.
2. ASA Relative Value Guide (RVG) — American Society of Anesthesiologists. Annual publication establishing base units and physical status unit values for all anesthesia codes. Verify current-year values; base units cited in this article reflect ASA RVG training knowledge.
3. CMS NCCI Policy Manual — Updated quarterly. Governs bundling rules, PTP edits, and MUE values for anesthesia claims.
4. CMS Physician Fee Schedule Final Rule — Published annually each November, effective January 1. Sets the anesthesia conversion factor and payment rules for the calendar year.