Bariatric surgery is reserved for individuals who are severely obese as defined by body mass index, or BMI. The BMI is calculated by dividing a patient's weight in kilograms by the square of their height in meters. Alternatively, BMI equals the patient's weight
in pounds divided by the square of their height in inches and multiplied by 703. BMI is measured in units of kg per m2. A BMI between 18 and 25 kg/m2 is considered normal. Individuals are considered candidates for bariatric surgery when their BMI is greater than 40 kg/m2, or greater than 35 kg/m2 with one or more comorbidities including severe hypertension, sleep apnea, or diabetes. For most patients, this BMI corresponds to being approximately 45 kg (100 lb) or more above ideal body weight .
A number of different bariatric procedures are currently performed in the United States. Currently, Roux-en-Y gastric bypass (RYGB) is the most common operation (Fig. 6.1). In the RYGB, a surgical stapler is used to divide the stomach into a small upper pouch and a large gastric remnant. The upper pouch, only 15 to 30 ml in volume, causes the patient to feel full after eating a small meal. The small intestine is reconnected in a Y shape to the gastric pouch in such a manner that the ingested food bypasses the stomach, duodenum, and proximal jejunum. In addition to the volume restriction caused by the small pouch, the RYGB causes weight loss by decreasing absorption (malabsorption) and altering levels of hormones involved in weight maintenance, such as insulin and ghrelin .
The adjustable gastric band (AGB) is the second most common bariatric operation in the United States (Fig. 6.2). In this operation, commonly referred to as the Lap-Band® (Allergan, Irvine, Calif.), a small adjustable ring made of silicone rubber is wrapped around the upper portion of the stomach, creating a pouch of 15- to 20-ml volume .
Fig. 6.1. Diagram of the Roux-en-Y gastric bypass operation. (Image ©2005 Daniel M. Herron, reprinted with permission)
The band is connected, via a thin flexible tube, to an access port placed underneath the skin on the abdominal wall. By injecting or withdrawing saline from the access port, the band can be tightened or loosened and the amount of restriction adjusted. Unlike the RYGB, the AGB is a purely restrictive operation.
Vertical banded gastroplasty, also known as VBG or "stomach stapling," was at one time the most common bariatric operation, but has lost favor recently due to its poor long-term results . Like the adjustable gastric band, the VBG is a purely restrictive operation that works by decreasing the volume of food that a patient can eat at one sitting. Unlike the gastric band, the VBG cannot be adjusted. VBG is now an uncommon operation.
One of the most recently developed bariatric operations is the sleeve gastrectomy (SG), a more modern variant of the VBG (Fig. 6.3) . In this technically straightforward operation, the entire left side of the stomach is surgically removed, resulting in a small, banana-shaped stomach. For superobese patients in whom a complex operation like the RYGB may present excessive technical difficulty, the SG can be used as the first component of a two-staged approach. The SG will result in a weight loss of 50 kg or more, after which the patient can be safely taken to the operating room for conversion to a more definitive operation like the RYGB . SG without a second stage may also be used as a purely restrictive procedure.
The least common and most complex bariatric operation performed in the United States is the biliopancreatic diversion with duodenal switch (BPD-DS, Fig. 6.4) . The BPD-DS consists of a SG combined with the bypass of a substantial portion of the small intestine. The first portion of the duodenum is divided and reconnected to the
Fig. 6.3. Diagram of the sleeve gastrectomy. (Image ©2005 Daniel M. Herron, reprinted with permission)
Fig. 6.4. Diagram of the biliopancreatic diversion with duodenal switch (BDP-DA). (Image ©2005 Daniel M. Herron, reprinted with permission)
distal 250 cm of small intestine. Additionally, bile and pancreatic secretions are diverted to the distal ileum. The BPD-DS results in moderate volume restriction and significant malabsorption. While providing the best long-term weight loss of any bariatric operation, the BPD-DS causes the most nutritional disturbance.
6.4 weight loss after surgery and postoperative recommendations for pregnancy
The rate of weight loss after surgery varies with the type of procedure. A large meta-analysis of surgical interventions for weight loss reported a mean weight loss regardless of operation of 61.2% . Specifically, excess body weight loss was 47.5% for patients who underwent AGB, 61.6% for those who underwent RYGB, and 70.1% for those who had BPD-DS.
With the RYGB and BPD-DS, the most rapid weight loss occurs during the first 3 weeks after surgery, when patients typically lose 1 lb per day or more. The rate of weight loss gradually decreases until weight stabilizes, about 12 to 18 months after surgery . Weight loss after AGB occurs at a slower rate, but may continue for 2 to 3 years after surgery. Most bariatric surgeons recommend that female patients avoid pregnancy for a period of 18 months or more after their operation or until their weight has stabilized.
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