There is not a lot of information out there for the AD modifier but below are two links of articles that I was aware of.
http://www.wpsmedicare.com/j8macpartb/resources/modifiers/modifier-ad-update.shtml
Modifier AD Update
Date February 2012
State Indiana
Description of Update/Status
Claims for anesthesia services using modifier AD - Medically supervised by a physician, more than four concurrent anesthesia procedures - allows for three base units without a time factor unless the physician documents they were "present on induction."
Resolution
The Centers for Medicare & Medicaid Services (CMS) Internet Only Manual (IOM) Publication 100-04, Chapter 12, Section 50 indicates that where a physician has medically supervised more than four concurrent procedures, the allowed amount is based on three base units and one time unit if the physician documents they were "present on induction."
Actions
Beginning April 1, 2013 WPS Medicare will provide reimbursement for three base units plus one time unit when the physician is present on induction. If the physician does not document he/she was present on induction, WPS Medicare will reimburse based on three base units without time. Providers should continue to convert hours into minutes and submit the total minutes in Box 24G of the CMS 1500 form or the Loop 2400 Segment 2-3700-SV104 in the 5010 electronic format.
http://www.palmettogba.com/palmetto... Medicare~Articles~Modifier Lookup~8EELAB1511
HCPCS Modifier AD
Description:
Medical supervision by a physician: more than four concurrent anesthesia procedures
Guidelines/Instructions: •This modifier may only be submitted with anesthesia procedure codes (e.g., CPT codes 00100 through 01999). 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.
•The units field must always be '1' when this modifier is submitted
Physician services may be reimbursed at the medically supervised rate in the following situations: •The anesthesiologist is involved in furnishing more than four procedures concurrently
•The anesthesiologist is performing other services while directing the concurrent procedures. There are several exceptions to this requirement: ◦Addressing an emergency of short duration in the immediate area
◦Administering an epidural or caudal anesthetic to ease labor pain
◦Periodic (rather than continuous) monitoring of an obstetrical patient
◦Receiving patients entering the operating suite for the next surgery
◦Checking or discharging patients in the recovery room
◦Handling scheduling matters
•These exceptions do not apply if the physician: ◦Leaves the operating suite for other than short durations
◦Devotes extensive time to an emergency case
◦Is otherwise not available to respond to the immediate needs of surgical patient
Reference:
•CMS Pub. 100-04, Chapter 12 external link (PDF, 1 MB) ◦Definitions of personally performed, medically directed and medically supervised: Section 50
◦Definition of concurrent procedures: Section 50J
◦Anesthesia modifiers: Section 50K
◦Base units for anesthesia services: following Section 50K: Exhibit 1