CMS to ASA Base Unit Value Comparison

By: Hal Nelson, CANPC
Vice President, Anesthesiology Services
MSN Healthcare Solutions

Payment Calculations for Anesthesia Services

Payment for anesthesia services is calculated by insurance plans using a formula of: 
“Base Units x Time Units”, multiplied by the payor’s Conversion Factor.

Base units include the standard pre-operative and post-operative visits, administration of fluids and blood products incident to the anesthesia care and interpretation of non-invasive physiological monitoring.  Essentially, these units describe the complexity of the surgery and are valued from 3 to 30, depending upon the procedure.

While you’d think they would be the same for all insurance companies, they’re not. Eight codes in particular, are valued less by CMS than the ASA Relative Value Guide. There are also some commercial/managed care plans which use the lower-valued CMS base units.

To ensure that your future revenue projections are accurate, we recommend using the attached list and confirming the base unit methodology which your main payors utilize.

CMS to ASA base unit value comparison 1
CMS to ASA base unit value comparison 2
CMS to ASA base unit value comparison 3
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CMS to ASA base unit value comparison 6
Hal Nelson, Vice President Anesthesiology Services


VP of Anesthesiology Services

Hal has 30+ years of experience on both the payor and RCM side, with a focus in Anesthesia. He formerly worked as a senior claims approver at United Healthcare, as well as a compliance officer for multiple national anesthesia billing companies. His broad-based experience ensures that MSN clients have a resource for documentation and billing issues. His past speaking engagements include ASA, MGMA, Dartmouth, and Johns Hopkins.

This educational guide was prepared as a tool to provide education for documentation and coding. It is not intended to affect clinical treatment patterns. The material provided is for informational purposes only. Efforts have been made to ensure the information within this document was accurate on the date of distribution. Reimbursement policies vary from insurer to insurer and the policies of the same payer may vary within different U.S. regions. All policies should be verified to ensure compliance. CPT® codes, descriptions and other data are copyright of the American Medical Association (or such other date of publication of CPT®).All Rights Reserved. CPT® is a registered trademark of the American Medical Association. Proprietary and confidential document.  All rights reserved. No part of this document may be reproduced or used in any manner without the written permission of MSN Healthcare Solutions, LLC.

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