Typically, an anesthesia bill for services provided by an Anesthesiologist (Medical Doctor) and/or a CRNA (Certified Registered Nurse Anesthetist), is broken into three parts. Each part is assigned a unit value.

1. The anesthetic procedure is first assigned a number of base units based on the complexity of the procedure. For example, an appendectomy is assigned six units while an invasive heart case is assigned 20 base units.
2. The amount of time the procedure requires is calculated according to time units. Billable time starts when the anesthesia provider begins preparation of the patient for anesthesia in the operating room or equivalent area, and ends when the patient is safely placed under post-anesthetic supervision and care. The amount of time assigned per unit varies throughout the United States from 6 to 15 minute increments.
3. Physical status and/or qualifying circumstances that affect the risk of the procedure are documented through the use of modifiers to the procedure (Common Procedural Terminology or CPT) code. Each modifier is also assigned a unit value. Modifiers such as physical status, age and emergency factors may be added to the procedure code. The total number of units is then multiplied by a conversion value to create a total charge for the procedure.

An illustration of the formula by which an anesthesia charge is calculated is illustrated below: 
(Base units + Time units + Modifying units) x $ Conversion Factor = Anesthesia Charge

Billing for the Anesthesiologist (M.D.) & Nurse Anesthetist (CRNA)

CRNAs within a given facility who are no longer employed by the facility (although most are despite recent changes in regulations allowing them more autonomy) have generally created their own group and received provider numbers with which to bill and be reimbursed for their services. In such circumstances, third party payers/patients receive three separate bills relating to the provision of anesthesia care: one for the professional services of the Anesthesiologist, a second for the professional services of the CRNA and a third from the facility for use of its anesthesia equipment, supplies and medications. CRNAs employed by an anesthesiology group can be billed separately or under a global fee, where the professional fees of the Anesthesiologist and CRNA are combined, depending on third party payer guidelines and regulations.

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