Surgery for morbid obesity, termed bariatric surgery, falls into two general categories: 1) gastric-restrictive procedures that create a small gastric pouch, resulting in weight loss by producing early satiety and thus decreasing dietary intake; and 2) malabsorptive procedures, which produce weight loss due to malabsorption by altering the normal transit of ingested food through the intestinal tract. Some bariatric procedures may include both a restrictive and a malabsorptive component.
Bariatric surgery is performed for the treatment of morbid (clinically severe) obesity. Morbid obesity is defined as a body mass index (BMI) greater than 40 kg/m² or a BMI greater than 35 kg/m² with associated complications including, but not limited to hypertension, dyslipidemia, diabetes, coronary artery disease, obstructive sleep apnea or osteoarthritis. Morbid obesity results in a very high risk for weight-related complications, such as diabetes, hypertension, obstructive sleep apnea, and various types of cancers (for men: colon, rectum, and prostate; for women: breast, uterus, and ovaries), and a shortened life span. A morbidly obese man at age 20 can expect to live 13 years less than his counterpart with a normal BMI, which equates to a 22% reduction in life expectancy.
The first treatment of morbid obesity is dietary and lifestyle changes. Although this strategy may be effective in some patients, only a few morbidly obese individuals can reduce and control weight through diet and exercise. The majority of patients find it difficult to comply with these lifestyle modifications on a long-term basis.
When conservative measures fail, some patients may consider surgical approaches. A 1991 National Institutes of Health (NIH) Consensus Conference defined surgical candidates as those patients with a BMI of greater than 40 kg/m2, or greater than 35 kg/m2 in conjunction with severe comorbidities such as cardiopulmonary complications or severe diabetes.
Resolution (cure) or improvement of type 2 diabetes mellitus after bariatric surgery and observations that glycemic control may improve immediately after surgery, before a significant amount of weight is lost, have promoted interest in a surgical approach to treatment of type 2 diabetes. The various surgical procedures have different effects, and gastrointestinal rearrangement seems to confer additional anti-diabetic benefits independent of weight loss and caloric restriction. The precise mechanisms are not clear, and multiple mechanisms maybe involved. Gastrointestinal peptides, glucagon-like peptide-1 (1GLP-1), glucose-dependent insulinotropic peptide (GIP), and peptide YY (PYY) are secreted in response to contact with unabsorbed nutrients and by vagally mediated parasympathetic neural mechanisms.GLP-1 is secreted by the L cells of the distal ileum in response to ingested nutrients and acts on pancreatic islets to augment glucose-dependent insulin secretion. It also slows gastric emptying, which delays digestion, blunts postprandial glycemia, and acts on the central nervous system to induce satiety and decrease food intake. Other effects may improve insulin sensitivity. GIP acts on pancreatic beta cells to increase insulin secretion through the same mechanisms as GLP-1, although it is less potent. PYY is also secreted by the L cells of the distal intestine and increases satiety and delays gastric emptying.
MEDICAL MANAGEMENT OF MORBID OBESITY
The Society of Gastrointestinal and Endoscopic Surgeons (SAGES) states the treatment of morbid obesity should be dietary, exercise, and behavior modification with possible prescription medications under the management of a physician. Although this strategy may be effective in some patients, frequently the weight loss is not durable with only 5% to 10% of patients maintaining the weight loss for more than a few years. When conservative measures fail, some patients may consider surgical approaches. The1998 National Institutes of Health (NIH) Clinical Guidelines and the 1991 NIH Consensus Conference identified surgery as an option in those patients with a BMI of greater than 40 kg/m2, or greater than 35 kg/m2 in conjunction with severe comorbidities related to obesity such as cardiopulmonary complications or severe diabetes. Super obesity has been described as a BMI greater than 50 kg/m2.
SURGICAL MANAGEMENT FOR MORBID OBESITY
The following summarizes the different types of bariatric surgery procedures.
GASTRIC RESTRICTIVE PROCEDURES
1. Vertical-Banded Gastroplasty (VBG)
Vertical-banded gastroplasty was formerly one of the most common gastric restrictive procedures performed in the U.S. but has now been essentially replaced by other restrictive procedures due to high rates of revisions and reoperations. In this procedure, the stomach is segmented along its vertical axis to create a durable reinforced and rate-limiting stoma at the distal end of the pouch. A plug of stomach is then removed and a propylene collar is placed through this hole and then stapled to itself. Because the normal flow of food is preserved, metabolic complications are rare. Complications include esophageal reflux, dilation or obstruction of the stoma, with the latter two requiring reoperation. Dilation of the stoma is a common reason for weight regain. Vertical banded gastroplasty may be performed using an open or laparoscopic approach.
2. Adjustable Gastric Banding (AGB) or (LAGB®)
Adjustable gastric banding involves placing a gastric band around the exterior of the stomach. The band is attached to a reservoir that is implanted subcutaneously in the rectus sheath. Injecting the reservoir with saline will alter the diameter of the inner lining of the gastric band; therefore, the rate-limiting stoma in the stomach can be progressively narrowed to induce greater weight loss, or expanded if complications develop. Because the stomach is not entered, the surgery and any revisions (if necessary) are relatively simple. Complications include slippage of the external band or band erosion through the gastric wall. Adjustable gastric banding has been widely used in Europe; currently, one such device is approved by the U.S. Food and Drug Administration (FDA) for marketing in the U.S., Lap-Band (BioEnterics, Carpinteria, CA). The labeled indications for this device are as follows:
"The Lap-Band system is indicated for use in weight reduction for severely obese patients with a body mass index (BMI) of at least 40 or a BMI of at least 35 with one or more severe comorbid conditions, or those who are 100 lbs or more over their estimated ideal weight according to the 1983 Metropolitan Life Insurance Tables (use the midpoint for medium frame). It is indicated for use only in severely obese adult patients who have failed more conservative weight-reduction alternatives, such as supervised diet, exercise and behavior modification programs. Patients who elect to have this surgery must make the commitment to accept significant changes in their eating habits for the rest of their lives."
A second adjustable gastric banding device was approved by the FDA through the Premarket Approval (PMA) process in September 2007, the REALIZE® model (Ethicon Endo-Surgery, Cincinnati, OH). Labeled indications for this device are as listed below:
“The [REALIZE] device is indicated for weight reduction for morbidly obese patients and is indicated for individuals with a BMI of at least 40 kg/m2, or a BMI of at least 35 kg/m2 with one or more comorbid conditions. The band is indicated for use only in morbidly obese adult patients who have failed more conservative weight-reduction alternatives, such as supervised diet, exercise, and behavior modification programs.”
3. Open Gastric Bypass with Roux-en-Y short-limb (<150cm) (GBY or RYGB)
The original gastric bypass surgeries were based on the observation that post-gastrectomy patients tended to lose weight. The current procedure involves both a restrictive and a malabsorptive component, with horizontal or vertical partition of the stomach in association with a Roux-en-Y procedure (i.e., a gastrojejunal anastomosis). Thus, the flow of food bypasses the duodenum and proximal small bowel. The procedure may also be associated with an unpleasant dumping syndrome in which a large osmotic load delivered directly to the jejunum from the stomach produces abdominal pain and/or vomiting. The dumping syndrome may further reduce intake, particularly in sweets eaters. Operative complications include leakage and marginal ulceration at the anastomotic site. Because the normal flow of food is disrupted there are more metabolic complications compared to other gastric restrictive procedures. These complications include iron deficiency anemia, vitamin B-12 deficiency, and hypocalcemia (all of which can be corrected by oral supplementation). Another concern is the ability to evaluate the blind bypassed portion of the stomach.
4. Laparoscopic Gastric Bypass
Introduced in 2005, laparoscopic gastric bypass is the laparoscopic version of the open gastric bypass described above.
5. Mini Gastric Bypass
Recently a variant of the gastric bypass called the mini-gastric bypass has been popularized. Using a laparoscopic approach the stomach is segmented (similar to a traditional gastric bypass), but instead of creating a Roux-en-Y anastomosis the jejunum is anastomosed directly to the stomach (similar to a Billroth II procedure). The type of anastomosis used makes this procedure unique.
6. Sleeve Gastrectomy (SG)
A ‘sleeve’ gastrectomy is an alternative approach to gastrectomy that can be performed on its own, or in combination with malabsorptive procedures (most commonly biliopancreatic diversion with duodenal switch). In this procedure, the greater curvature of the stomach is resected from the angle of His to the distal antrum, resulting in a stomach remnant shaped like a tube or ‘sleeve’. The pyloric sphincter is preserved, resulting in a more physiologic transit of food from the stomach to the duodenum, and avoiding the ‘dumping syndrome’ (overly rapid transport of food through stomach into intestines) that is seen with distal gastrectomy. The sleeve gastrectomy procedure is relatively simple to perform, and can be done by the open or laparoscopic technique. Some surgeons have proposed this as the first in a two-stage procedure for very high-risk patients. Weight loss following sleeve gastrectomy may improve a patient’s overall medical status, and thus reduce the risk of a subsequent more extensive malabsorptive procedure, such as biliopancreatic diversion.
7. Endoluminal (also called endosurgical, endoscopic, or natural orifice) bariatric procedures
With these procedures access to the relevant anatomical structures is gained through the mouth without skin incisions. Primary and revision bariatric procedures are being developed to reduce the risks associated with open and laparoscopic interventions. Examples of endoluminal bariatric procedures studies include gastroplasty using a transoral endoscopically guided stapler and placement of devices such as a duodenal-jejunal sleeve and gastric balloon.
The multiple variants of malabsorptive procedures differ in the lengths of the alimentary limb, the biliopancreatic limb, and the common limb, in which the alimentary and biliopancreatic limbs are anastomosed. These procedures also may include an element of a restrictive surgery based on the size of the stomach pouch. The degree of malabsorption is related to the length of the alimentary and common limbs. For example, a shorter alimentary limb (i.e., the greater the amount of intestine that is excluded from the nutrient flow) will be associated with malabsorption of a variety of nutrients, while a short common limb (i.e., the biliopancreatic juices are allowed to mix with nutrients for only a short segment) will primarily limit absorption of fat.
1. Biliopancreatic Bypass Diversion Procedure (also known as the Scopinaro procedure) (BPB)
The biliopancreatic bypass (BPB) procedure, developed and used extensively in Italy, was designed to address some of the drawbacks of the original intestinal bypass procedures that have been abandoned due to unacceptable metabolic complications. Many of the complications were thought to be related to bacterial overgrowth and toxin production in the blind, bypassed segment. In contrast, BPB consists of a subtotal gastrectomy and diversion of the biliopancreatic juices into the distal ileum by a long Roux-en-Y procedure. The procedure consists of the following components:
- A distal gastrectomy functions to induce a temporary early satiety and/or the dumping syndrome in the early postoperative period, both of which limit food intake.
- A 200 cm long alimentary tract consists of 200 cm of ileum connecting the stomach to a common distal segment.
- A 300-400 cm biliary tract, which connects the duodenum, jejunum, and remaining ileum to the common distal segment.
- A 50-100 cm common tract where food from the alimentary tract mixes with biliopancreatic juices from the biliary tract. Food digestion and absorption, particularly of fats and starches, are therefore limited to this small segment of bowel, i.e., creating a selective malabsorption. The length of the common segment will influence the degree of malabsorption.
- Because of the high incidence of cholelithiasis associated with the procedure, patients typically undergo an associated cholecystectomy.
There are many potential metabolic complications related to biliopancreatic bypass, including most prominently iron deficiency anemia, protein malnutrition, hypocalcemia, and bone demineralization. Protein malnutrition may require treatment with total parenteral nutrition. In addition, there have been several case reports of liver failure resulting in liver transplant or death.
2. Biliopancreatic Bypass Diversion with Duodenal Switch
The duodenal switch procedure is essentially a variant of the biliopancreatic bypass described above. However, instead of performing a distal gastrectomy, a sleeve gastrectomy is performed along the vertical axis of the stomach preserving the pylorus and initial segment of the duodenum. This is then anastomosed to a segment of the ileum similar to the biliopancreatic bypass, to create the alimentary segment. Preservation of the pyloric sphincter is intended to ameliorate the dumping syndrome and decrease the incidence of ulcers at the duodenoileal anastomosis by providing a more physiologic transfer of stomach contents to the duodenum. The sleeve gastrectomy decreases the volume of the stomach and decreases the parietal cell mass. However, the basic principle of the procedure is similar to that of the biliopancreatic bypass, i.e., producing selective malabsorption by limiting the food digestion and absorption to a short common ileal segment.
3. Gastric Bypass with Long-Limb (i.e., > 150cm)
Recently variations of gastric bypass procedures have been described that consist primarily of long limb Roux-en-Y procedures, which vary in the length of the alimentary and common limbs. For example, the stomach may be divided with a long segment of the jejunum (instead of ileum) anastomosed to the proximal gastric stump to create the alimentary limb. The remaining pancreaticobiliary limb (consisting of stomach remnant, duodenum, and length of proximal jejunum) is then anastomosed to the ileum creating a common limb of variable length in which the ingested food mixes with the pancreaticobiliary juices. The stomach may be bypassed in a variety of ways, i.e., either by resection or stapling along the horizontal or vertical axis. Unlike the traditional gastric bypass (essentially a gastric restrictive procedure), these very long limb Roux-en-Y gastric bypasses function as a malabsorptive procedure, depending on the location of the anastomoses.
4. Laparoscopic Malabsorptive Procedure
This describes any of the malabsorptive/restrictive procedures done by laparoscopy.