Last updated: 11/24/2009

Several types of malabsorptive procedures, meaning procedures that are intended to lower caloric intake, may be used to perform gastric bypass surgery, including:

• gastric bypass with long gastrojejunostomy
• Roux-en-Y (RNY) gastric bypass
• transected (Miller) Roux-en-Y bypass
• laparoscopic RNY bypass
• vertical (Fobi) gastric bypass
• distal Roux-en-Y bypass
• biliopancreatic diversion

All procedures aim to restrict food intake and differ in the surgical approach used to create a smaller stomach. Choice of procedure relies on the patient's overall health status and on the surgeon's judgement and experience.

In the operating room, the patient is first put under general anesthesia by the anesthesiologist. Once the patient is asleep, an endotracheal tube is placed through the mouth of the patient into the trachea (windpipe) to connect the patient to a respirator during surgery. A urinary catheter is also placed in the bladder to drain urine during surgery and for the first two days after surgery. This also allows the surgeon to monitor the patient's hydration. A nasogastric (NG) tube is also placed through the nose to drain secretions and is typically removed the morning after surgery.

In most clinics and hospitals, the operation of choice for obese people is the RNY gastric bypass, which has the endorsement of the National Institutes of Health (NIH). The surgeon starts by creating a small pouch from the patient's original stomach. When completed, the pouch will be completely separated from the remainder of the stomach and will become the patient's new stomach. The original stomach is first separated into two sections. The upper part is made into a very small pouch about the size of an egg that can initially hold 1–2 oz (30–60 ml), as compared to the 40–50 oz (1.2–1.5 l) held by a normal stomach. It is created along the more muscular side of the stomach, which makes it less likely to stretch over time. This procedure will allow food to proceed from the mouth to the esophagus, into the gastric pouch, and then immediately into the part of the small bowel called the jejunum (or Roux limb). Food no longer goes to the larger portion of the stomach. Because none of the original stomach is removed, its secretions can travel to the duodenum. The two parts of the stomach are thus completely separated and are closed by stapling and sewing to eliminate the possibility of leaks. Scar tissue eventually forms at the stapled and sewn area so that the pouch and stomach are permanently separated and sealed. Finally, the surgeon reconnects the first part of the jejunum and the duodenum containing the juices from the stomach, pancreas, and liver (the biliopancreatic limb) to the segment of small bowel that was connected to the gastric pouch (the Roux limb).

The opening between the new stomach and the small bowel is called a stoma. It has a diameter of some 0.31 in (0.8 cm). All food goes into the new small stomach and must then pass through this narrow stoma before entering the small intestine. The part of the small intestine from the upper functioning small stomach and the part of the small intestine from the initial lower stomach are joined in a Y connection so that the gastric juices can mix with the food coming from the small pouch.

The RNY can also be performed laparoscopically. The result is the same as an open surgery RNY, except that instead of opening the patient with a long incision on the stomach, surgeons make a small incision and insert a pencil-thin optical instument, called a laparoscope, to project a picture to a TV monitor. The laparoscopic RNY results in smaller scars, and usually only three to four small incisions are made. The average time required to complete the laparoscopic RNY gastric bypass is approximately two hours.