Surgical Treatment of Obesity

Demographics

Obesity has reached epidemic proportions in the United States. The number of obese persons increased by 34% from 2000 to 2016. Nearly 40% of adults and 18% of children are now obese. In Hispanic and black populations, the prevalence is near 50% for adults. Worldwide, the number of overweight people has increased to approximately 38%, with 500 million now obese.

Patients with a body mass index (BMI) between 25 and 29.9 are considered overweight, and a BMI greater than 30 is considered obese. Other factors, such as fat distribution and weight gain, modify the risk within each BMI category. One of the etiologies of obesity derives by the ingestion of more calories than are expended, so excess calories are stored as fat. However, genetic and environmental factors contribute to obesity. The marked increase in obesity in the past 20 years cannot be attributed to genetic factors alone and are most likely caused by changes in the environment.

Obesity is responsible for at least 30 other diseases. Type 2 diabetes (T2DM) is associated with severe obesity in 20% of patients. Hypertension, hyperlipidemia, obstructive sleep apnea (OSA), hypoventilation, asthma, gastroesophageal reflux disease (GERD), coronary artery disease (CAD), chronic heart failure (CHF), cerebrovascular accident (CVA, stroke), nonalcoholic steatohepatitis (NASH), low back pain, degenerative joint disease (DJD), pseudotumor cerebri, urinary stress incontinence, and polycystic ovary syndrome (PCOS) are all associated with obesity. Furthermore, as released by the Office of Disease Control, approximately 40% of cancers are associated with obesity and 55% of those in obese females. The most common type of cancers that are associated with obese patients are esophagus, uterus, breast, prostate, liver, and kidney. Patients are also prone to ventral and incisional hernias. Severely obese people are at risk for mental disorders, including depression and anxiety, as well as eating disorders.

Even the fat distribution in the body plays a role in the prevalence of comorbidities. In fact, persons with increased abdominal fat are at increased risk for diabetes, hypertension, hyperlipidemia, and ischemic heart disease (metabolic syndrome) compared with those with increased gluteal and femoral fat ( Fig. 191.1 ).

As a result, the increased BMI translates to a decreased life span. Severely obese women are twice as likely to die as those of normal weight. The increase in prevalence of obesity worldwide and its growing effect on related medical diseases and mortality have empowered both medical and surgical efforts to combat this growing epidemic.

Among the different potential and popular treatments for obesity are diets, behavioral modifications, and physical activity. Dietary modification should encourage patients to eat three meals daily, to avoid snacking between meals, to avoid energy-dense and high-fat foods, and to increase the intake of fruits and vegetables. Physical activity is also important for overall health for cardiovascular benefits but is not helpful in achieving meaningful weight loss without reduction of caloric intake.

The next level of treatment includes pharmacotherapy because it can help selected patients to achieve and maintain weight loss. Patients receiving pharmacotherapy for obesity should also be involved in efforts to change their lifestyles, including developing the habits of healthy eating and adequate exercise. Weight loss is usually 3 to 5 kg over placebo, but the weight tends to be regained once the medications are discontinued.

Surgery is the most effective approach for achieving weight loss in the extremely obese patient (BMI ≥ 40). Indications for surgery include BMI greater than 40 or BMI between 35 and 40 and severe obesity-related diseases, such as diabetes and OSA. Serious psychiatric disorders are absolute contraindications for surgery. Of the various types of obesity surgery, the gastric bypass procedure, also known as the Roux-en-Y, and the sleeve gastrectomy (SG), are the most popular.

Indications

Surgical therapy focuses on those with a BMI of 35 kg/m ² or greater, although evidence now indicates that obese individuals with BMI lower than 35 may benefit from surgery as well, especially if they have T2DM.

Body mass index is the most practical and widely used measure of an individual's size. It is calculated by dividing the patient's weight in kilograms by the height in meters squared (kg/m ² ). In adults, BMI is categorized as follows:

• Underweight less than 18.5 kg/m ²

• Normal weight 18.5 to 24.9 kg/m ²

• Overweight 25 to 29.9 kg/m ²

• Class I obesity 30 to 34.9 kg/m ²

• Class II obesity 35 to 39.9 kg/m ²

• Class III obesity 40 to 49.9 kg/m ² (severely, extremely, or morbidly obese)

• Class IV obesity ≥50 kg/m ² (“super-obese”)

Bariatric surgery should be considered for patients who have failed medical management, such as dieting, exercise, and drug therapy. According to the National Institutes of Health, candidates for surgery should have a BMI greater than 40 or BMI greater than 35 and major comorbidity, such as T2DM, OSA, obesity-related cardiomyopathy, or DJD. Currently, patients with BMI greater than 30 (or as low as 27.5 in Asian population) with poorly controlled hyperglycemia should also be considered for bariatric surgery. The American Diabetes Association has also published similar guidelines in 2017. Patients must have tried to lose weight by medical methods, must be motivated, and must be informed about the procedure and potential consequences. They must also be an acceptable surgical risk.

Patients who may not be considered for surgery include those with unstable CAD, severe pulmonary disease, portal hypertension, or active substance abuse, as well as those unable to carry out the necessary postsurgical lifestyle changes. Contraindications also include untreated major depression or psychosis, active binge eating, or severe coagulopathy. Bariatric surgery has proven to be effective, safe, and beneficial in those older than 65 or younger than 18 years of age. These age limits that were considered in the past as a contraindication are now being relaxed as long-term positive outcome data in both populations are reported.

Preparation

Before surgical intervention, patients must attend an educational seminar and interact with former surgical patients. They receive a tutorial on the procedure, are evaluated by a psychiatric therapist, and meet with a nutritionist. Many patients will need to have sleep apnea ruled out if they have high BMI or severe symptoms. Cardiac and pulmonary evaluations are performed to assess the risk of anesthesia. Patients undergoing gastric bypass and SG are evaluated by upper endoscopy because, after the gastric pouch is created and the stomach is divided, access to the stomach is extremely difficult. In addition, the presence of Barrett esophagus is considered a relative contraindication in patients who are selected for SG. The preoperative endoscopic evaluation can recognize other important, acute and chronic pathologies such as hiatal hernias, masses, and ulcers. Patients also undergo blood testing for thyroid disease, liver disease, and T2DM. Postoperatively, patients are encouraged to follow up with nutrition and psychiatric support groups.

Types of Bariatric Procedures

Historically, the bariatric surgical procedures were classified according to their malabsorptive or restrictive mechanism. The restrictive procedures limit caloric intake by creating a small stomach pouch, ranging from virtual in the adjustable gastric band and to a long narrow gastric tube in the gastric sleeve. Weight loss depends on a decrease in caloric intake and therefore is more gradual.

The primary mechanism of malabsorptive procedures is to create rapidly emptying and diverting pathways for food and digestive substances so that they meet distally within the small-bowel lumen and therefore have a smaller length of absorptive surface area in which to interact. In addition, the rapid emptying of undigested food to the distal small bowel will stimulate incretins that participate in the remission of diabetes. The biliopancreatic diversion (BPD) and duodenal switch are examples of malabsorptive procedures. The Roux-en-Y gastric bypass (RYGB) combines features of both restriction and malabsorption with the creation of a small stomach pouch and a 25% to 30% functional small-bowel bypass. However, more modern classifications take into account other potential mechanisms of action of the bariatric procedures, such as modification of enterohormones, alterations in the complex brain-gut-pancreas-visceral fat axis, modification of bile salts, and modifications to the gut flora.

The trend now is toward minimally invasive approaches to bariatric surgery; studies show better cost effectiveness and safety than with open procedures ( Fig. 191.2 ).