Anesthesia services are reimbursed differently from other procedure codes. Part of the payment for anesthesia is based on 'base units,' which are assigned to anesthesia CPT codes by the Centers for Medicare & Medicaid Services (CMS). The remainder of the payment allowance is based on the time the patient was 'under anesthesia.'
Both the base and time units are then multiplied by an anesthesia conversion factor (CF), which CMS releases annually and is specific to the locality where the anesthesia service is rendered.
The formula to calculate the allowed amount for anesthesia is:
base units + time (in units) x CF = anesthesia fee amount
For a list of base units assigned to anesthesia CPT codes for 2018, please refer to the 2018 Anesthesia Base Units by CPT Code on the CMS website. The anesthesia base units are unchanged for calendar years 2019 and 2020. Prior years can be found in the CMS Anesthesiologists Center.
On the claim, report the actual anesthesia time in minutes. For example, 17 minutes of anesthesia time is reported as '0017' in the units' field or item 24G of the CMS-1500 claim form or its electronic equivalent.
Payment for services that meet the definition of 'personally performed' is based on base units (as defined by CMS) and time in increments of 15-minute units.
Time units are computed by dividing the reported anesthesia time by 15 minutes (17 minutes / 15 minutes = 1.13 units).
For physician-directed anesthesia services, the allowance for both the physician and the certified registered nurse anesthetist (CRNA) is 50% of the allowance for the anesthesia service if performed by the physician or CRNA alone.
Payment for services that are 'medically supervised' is based on three base units per procedure with an additional unit of time if the physician documents that he or she was present at induction.
To determine the medically directed rate, multiply the approved amount by 50%.
For more information regarding the definitions of 'personally performed' and 'medically directed' please refer to the CMS IOM Pub. 100-04, Claims Processing Manual, Chapter 12, Sections 50.B-50.D.