Anesthesia Coding
Anesthesia is a small but distinctive section with its own payment logic. Rather than relative value units, anesthesia uses a formula built from base units, time units, and modifying units. Understanding that formula — and the physical status and qualifying-circumstance add-ons that feed it — is enough to answer most anesthesia questions on the exam.
The anesthesia payment formula
Anesthesia charges are computed as (Base Units + Time Units + Modifying Units) × a locality-specific conversion factor. Base units are assigned to each anesthesia CPT code according to the complexity of the underlying procedure. Time units are counted from when the anesthesiologist begins preparing the patient until care is transferred at the end of the case, typically in 15-minute increments. Modifying units come from physical status and qualifying circumstances. This unit-and-time model is unique to anesthesia.
Physical status and qualifying circumstances
Physical status modifiers P1–P6 grade the patient: P1 normal healthy, P2 mild systemic disease, P3 severe systemic disease, P4 severe disease that is a constant threat to life, P5 moribund, P6 brain-dead organ donor. P3 and higher generally add modifying units. Qualifying circumstances are add-on codes for conditions that raise anesthesia risk — extreme age (under 1 or over 70), total body hypothermia, controlled hypotension, and emergency conditions. Both are layered on top of the primary anesthesia code.