POEM procedures. 1-a. A long submucosal tunnel is created. The blue color of the indigocarmine that was mixed with the glycerin solution helps discriminate the white muscle layer from submucosal tissue.1-b. Using a triangle-tip knife, the inner circular muscle is hooked and cut. Outer longitudinal muscles are seen behind the inner muscles. Outer muscles should be preserved to avoid severe complications such as compartment syndrome and mediastinitis.