Question: A patient needed general anesthesia during an EEG due to behavioral issues and autism. She also has a history of hypothyroidism and has random outbursts. The EEG was recommended to evaluate her for seizures. How should I code for this? California Subscriber Answer: Report unlisted code 01999 (Unlisted anesthesia procedure(s)) and append modifier 23 (Unusual anesthesia). Include thorough documentation of the service rendered, the patient’s history, and why the physicians believed anesthesia was necessary during the procedure. It is also a good idea to suggest a similar service to help the insurance claims processor understand the value of the services provided.