Factors that Impact Anesthesia services

This article will provide you some valuable information with examples about the factors impacting Anesthesia services. If you are a newbie to Anesthesia coding, I would suggest you to read the “10 steps in Anesthesia coding” in the below link before you read this page

Base units:


It is built into each ASA is a measure of the complexity of the care needed to provide safe analgesia to a patient.


  • Only one ASA code, the one with the highest base value, can be used in the formula to determine the final fee for service.
  • With multiple procedures, the procedure with the highest relative value to the surgeon may not be the highest base value to Anesthesia.
  • Any procedure around the head, neck or shoulder girdle requiring field avoidance, or any procedure requiring a position other than supine or lithotomy has a base value of 5 regardless of any lesser base value indicated in the Relative value guide.


Surgeon performs an excision of a benign tumor on the olecranon process.

CPT Code: 24120

ASA Code: 01740 (Anesthesia for open or surgical arthroscopic procedures of the elbow; not otherwise specified)

Base Units: 4

Time Units:


Anesthesia time begins when the anesthesia provider prepares the patient for the induction of anesthesia in the operating room or equivalent area and ends when the anesthesia provider is no longer in personal attendance (patient is safely placed under post-operative supervision.)


  • AMA and ASA recommend that one unit of time is equal to 15 minutes of anesthesia time.
  • Time is rounded up to the next unit after 7.5 minutes is reached.
  • Medicare requires the actual anesthesia time (total number of minutes) be reported in box 24G of the CMS – 1500 claim form.
  • Pre-op evaluation is not included in anesthesia time and is included in the base value of the anesthesia code.


30 minutes of Anesthesia administration is equal to two units. (30=15+15)

38 minutes of Anesthesia administration is rounded up to three units. (38=15+15+8)

37 minutes of Anesthesia administration is rounded down to two units. (37=15+15+7)

Conversion factor:


The conversion factor (CF) is the amount of money determined by your facility that is charged for each unit of anesthesia care provided.


  • The anesthesia conversion factors for each calendar year are listed by payment locality and are effective for the date the service was provided.
  • The participating physician anesthesia conversion factor is listed first, the non-participating physician anesthesia conversion factor is second, and the non-medically directed conversion factor is listed in the third column.
  • CMS releases the CF annually and is specific to the locality where the anesthesia service is rendered.


The example provided below is just for understanding purpose. Providers should check their current anesthesia conversion factors for correct fee amounts.

ASA code: 00830

Time: 120 minutes

Locality: Rest of state (participating physician)

Base units for 00830 = 4

Time units for 120 minutes of Anesthesia administration = 8

Conversion factor = $19.84

Anesthesia fee = (Time Units + Base Units+ Applicable units) x Conversion Factor

By applying all the values into the formula, the final fee would be calculated as below:

(8 + 4 + 0) x $19.84 = $238.08

The physician’s allowed amount would be $238.08. The physician reimbursement is calculated at 80% of the allowed amount.

From this example, you can understand the importance of every component in Anesthesia coding and how it impacts the fee value when you miss to code the appropriate units.



Concurrency is defined with regard to the maximum number of procedures that the physician is medically directing within the context of a single procedure and whether these other procedures overlap each other.


  • A provider can either be medically directing or supervising.
  • A medically directing provider can be involved in up to 4 concurrent cases.
  • A provider is considered as a supervising provider when they are involved in 5 or more concurrent cases or performs other services while directing other concurrent procedures.

Each concurrency level is identified by a unique modifier that indicates the type of provider and how many other providers are being medically directed by that provider.

Physical Status Modifiers:

These modifiers should be appended to CPT codes 00100 through 01999 (anesthesia service/procedure codes). The submission of a physical status modifier indicates that documentation is available in the patient’s records supporting the situation described by the modifier descriptor, and that these records will be provided in a timely manner for review upon request. Examples for each of the modifier are listed below:


Physical status modifier P1:

  • Healthy.
  • Non-smoking
  • No or minimal alcohol use.

Physical status modifier P2:

It includes mild diseases only without substantive functional limitations

  • current smoker,
  • social alcohol drinker,
  • pregnancy,
  • obesity( 30<BMI<40),
  • well controlled DM/HTN,

Physical status modifier P3:

It includes one or more moderate to severe diseases.

  • poorly controlled, DM or HTN,
  • COPD
  • morbid obesity (BMI≥40)
  • active hepatitis,
  • alcohol dependence or abuse,
  • implanted pacemaker,
  • moderate reduction of ejection fraction,
  • ESRD undergoing regularly scheduled dialysis,
  • premature infant PCA<60 weeks,
  • history (>3 months) of MI, CVA, TIA or CAD/stents

Physical status modifier P4:

It includes severe systemic disease that is constant threat to life.

  • recent (<3 months) MI, CVA, TIA, or CAD/stents,
  • ongoing cardiac ischemia or severe valve dysfunction,
  • severe reduction of ejection fraction,
  • ESRD not undergoing regularly scheduled dialysis

Physical status modifier P5:

  • ruptured abdominal/thoracic aneurysm,
  • massive trauma,
  • intracranial bleed with mass effect,
  • ischemic bowel in the face of significant cardiac pathology or multiple organ/system dysfunction

Physical status modifier P6:

A declared brain-dead patient whose organs are being removed for donor purposes

Qualifying Circumstances:

These are all add-on codes that can be reported with the Anesthesia services. It should be billed as separate line when these services are reasonable and necessary. The codes and the unit values are listed below:

99100 – Unit value = 1:

  • Anesthesia for patient of extreme age, younger than one year and older than 70 (List separately in addition to code for the primary anesthesia procedure)

99116 – Unit value = 5

  • Anesthesia complicated by utilization of total body hypothermia (List separately in addition to code for the primary anesthesia procedure)

99135 – Unit value = 5

  • Anesthesia complicated by utilization of controlled hypotension (List separately in addition to code for the primary anesthesia procedure).

99140 – Unit value = 2

  • Anesthesia complicated by emergency conditions (List separately in addition to code for the primary anesthesia procedure)


  • 00326 – Anesthesia for all procedures on the larynx and trachea in children younger than 1 year of age
  • 00561 – Anesthesia for procedures on heart, pericardial sac, and great vessels of chest; with pump oxygenator, younger than 1 year of age
  • 00834 – Anesthesia for hernia repairs in the lower abdomen not otherwise specified, younger than 1 year of age
  • 00836 – Anesthesia for hernia repairs in the lower abdomen not otherwise specified, infants younger than 37 weeks gestational age at birth and younger than 50 weeks gestational age at time of surgery

Happy learning! Happy Coding!



1 Comment

  • Verla

    April 13, 2020 4:04 am

    I like reading through an article that can make people think.
    Also, many thanks for allowing for me to comment!

Leave a Reply