Gastric bypass, also called Roux-en-Y gastric bypass (RNY), is a type of weight-loss surgery that involves creating a small pouch from the stomach and the creation of a roux limb.  The roux limb is anastomosed to the gastric pouch and a second anastomosis connects the biliopancreatic limb to the roux limb. After gastric bypass, swallowed food will go into this small pouch of stomach and then directly into the roux limb thereby bypassing the excluded stomach and the first section of the small intestine.

With RNY Gastric Bypass, there is a great deal of variability in the steps of the procedure.  Surgeons may start with pouch creation or roux limb creation.  Likewise, there is a great variability in measurements of the pouch, bilio-pancreatic limb, and roux limb.  Techniques for anastomoses and pouch creation also vary widely.