Ask Dr. Z

"The patient had a previous fem-pop bypass using an in situ vein. He has now developed a tight stenosis in the segment of the vein from the knee down into the anastomosis and has had two catheter interventions, so that part is pretty much stented all the way into the native artery. Decision is made to revise this with a new bypass from the old bypass down onto the native posterior tibial artery. Cephalic vein is harvested for the bypass." We are unsure how to code the new bypass that is attached to the old (fem-pop) bypass down onto the native posterior tibial. Revision or new bypass? Can you please help with the codes?