Gastric bypass procedures (GBP) are any of a group of similar operations used to treat morbid obesity—the severe accumulation of excess weight as fatty tissue—and the health problems (comorbidities) it causes. Bariatric surgery is the term encompassing all of the surgical treatments for morbid obesity, not just gastric bypasses, which make up only one class of such operations.
A gastric bypass first divides the stomach into a small upper pouch and a much larger, lower "remnant" pouch and then re-arranges the small intestine to allow both pouches to stay connected to it. Surgeons have developed several different ways to reconnect the intestine, thus leading to several different GBP names. Any GBP leads to a marked reduction in the functional volume of the stomach, accompanied by an altered physiological and psychological response to food. The resulting weight loss, typically dramatic, markedly reduces comorbidities. The long-term mortality rate of gastric bypass patients has been shown to be reduced by up to 40%; however, complications are common and surgery-related death occurs within one month in 2% of patients.
Surgical indications
Gastric bypass is indicated for the surgical treatment of morbid obesity, a diagnosis which is made when the patient is seriously obese, has been unable to achieve satisfactory and sustained weight loss by dietary efforts, and is suffering from co-morbid conditions which are either life-threatening or a serious impairment to the quality of life.
In the past, serious obesity was interpreted to mean weighing at least 100 pounds (45 kg) more than the "ideal body weight", an actuarially determined body weight at which one was estimated to be likely to live the longest, as determined by the life insurance industry. This criterion failed for persons of short stature.
In 1991, the National Institutes of Health sponsored a consensus panel whose recommendations have set the current standard for consideration of surgical treatment, the body mass index (BMI). The BMI is defined as the body weight (in kilograms), divided by the square of the height (in meters). The result is expressed as a number usually between 20 and 70, in units of kilograms per square meter.
The Consensus Panel of the National Institutes of Health (NIH) recommended the following criteria for consideration of bariatric surgery, including gastric bypass procedures:
- People who have a body mass index (BMI) of 40 or higher. Or,
- People with a BMI of 35 or higher with one or more related comorbid conditions.
The Consensus Panel also emphasized the necessity of multidisciplinary care of the bariatric surgical patient, by a team of physicians and therapists, to manage associated co-morbidities, nutrition, physical activity, behavior and psychological needs. The surgical procedure is best regarded as a tool which enables the patient to alter lifestyle and eating habits, and to achieve effective and permanent management of their obesity and eating behavior.
Since 1991, major developments in the field of bariatric surgery, particularly laparoscopy, have outdated some of the conclusions of the NIH panel. In 2004, a Consensus Conference was sponsored by the American Society for Bariatric Surgery (ASBS), which updated the evidence and the conclusions of the NIH panel. This Conference, composed of physicians and scientists of many disciplines, both surgical and non-surgical, reached several conclusions, amongst which were:
- Bariatric surgery is the most effective treatment for morbid obesity
- Gastric bypass is one of four types of operations for morbid obesity.
- Laparoscopic surgery is equally effective and as safe as open surgery.
- Patients should undergo comprehensive pre-operative evaluation, and have multi-disciplinary support, for optimum outcome.
Surgical techniques
The gastric bypass, in its various forms, accounts for a large majority of the bariatric surgical procedures performed. It is estimated that 200,000 such operations were performed in the United States in 2008. An increasing number of these operations are now performed by limited access techniques, termed "laparoscopy" .
Laparoscopic surgery is performed using several small incisions, or ports , one of which conveys a surgical telescope connected to a video camera, and others permit access of specialized operating instruments. The surgeon actually views his operation on a video screen. The method is also called limited access surgery, reflecting both the limitation on handling and feeling tissues, and also the limited resolution and two-dimensionality of the video image. With experience, a skilled laparoscopic surgeon can perform most procedures as expeditiously as with an open incision — with the option of using an incision should the need arise.
The Laparoscopic Gastric Bypass, Roux-en-Y , first performed in 1993, is regarded as one of the most difficult procedures to perform by limited access techniques, but use of this method has greatly popularized the operation, with benefits which include shortened hospital stay, reduced discomfort, shorter recovery time, less scarring, and minimal risk of incisional hernia.
Essential features
The gastric bypass procedure consists in essence of:
- Creation of a small, (15–30 mL/1–2 tbsp) thumb-sized pouch from the upper stomach, accompanied by bypass of the remaining stomach (about 400 mL and variable). This restricts the volume of food which can be eaten. The stomach may simply be partitioned (typically by the use of surgical staples), or it may be totally divided into two parts (also with staplers). Total division is usually advocated, to reduce the possibility that the two parts of the stomach will heal back together ("fistulize"), negating the operation.
- Re-construction of the GI tract to enable drainage of both segments of the stomach. The technique of this reconstruction produces several variants of the operation, which differ in the lengths of small bowel used, the degree to which food absorption is affected, and the likelihood of adverse nutritional effects.
Variations of the gastric bypass
Gastric bypass, Roux en-Y (proximal)
This variant is the most commonly employed gastric bypass technique, and is by far the most commonly performed bariatric procedure in the United States. It is the operation which is least likely to result in nutritional difficulties. The small bowel is divided about 45 cm (18 in) below the lower stomach outlet, and is re-arranged into a Y-configuration, to enable outflow of food from the small upper stomach pouch, via a "Roux limb". In the proximal version, the Y-intersection is formed near the upper (proximal) end of the small bowel. The Roux limb is constructed with a length of 80 to 150 cm (31 to 59 in), preserving most of the small bowel for absorption of nutrients. The patient experiences very rapid onset of a sense of stomach-fullness, followed by a feeling of growing satiety, or "indifference" to food, shortly after the start of a meal.
Gastric bypass, Roux en-Y (distal)
The normal small bowel is 600 to 1,000 cm (20 to 33 ft) in length. As the Y-connection is moved farther down the Gastrointestinal tract, the amount of bowel capable of fully absorbing nutrients is progressively reduced, in pursuit of greater effectiveness of the operation. The Y-connection is formed much closer to the lower (distal) end of the small bowel, usually 100 to 150 cm (39 to 59 in) from the lower end of the bowel, causing reduced absorption (mal-absorption) of food, primarily of fats and starches, but also of various minerals, and the fat-soluble vitamins. The unabsorbed fats and starches pass into the large intestine, where bacterial actions may act on them to produce irritants and malodorous gases. These increasing nutritional effects are traded for a relatively modest increase in total weight loss.
Loop Gastric bypass ("Mini-gastric bypass")
The first use of the gastric bypass, in 1967, used a loop of small bowel for re-construction, rather than a Y-construction as is prevalent today. Although simpler to create, this approach allowed bile and pancreatic enzymes from the small bowel to enter the esophagus, sometimes causing severe inflammation and ulceration of either the stomach or the lower esophagus. If a leak into the abdomen occurs, this corrosive fluid can cause severe consequences. Numerous studies show the loop reconstruction (Billroth II gastrojejunostomy) works more safely when placed low on the stomach, but can be a disaster when placed adjacent to the esophagus. Thus even today thousands of "loops" are used for general surgical procedures such as ulcer surgery, stomach cancer and injury to the stomach, but bariatric surgeons abandoned use of the construction in the 1970s, when it was recognized that its risk is not justified for weight management.
The Mini-Gastric Bypass, which uses the loop reconstruction, has been suggested as an alternative to the Roux en-Y procedure, due to the simplicity of its construction, which reduced the challenge of laparoscopic surgery.
Physiology of the gastric bypass
The gastric bypass reduces the size of the stomach by well over 90%. A normal stomach can stretch, sometimes to over 1000 ml,
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