Bariatric Surgery

US Pharm. 2007;32(9):HS-27-HS-37.

For many individuals--especially those who are morbidly obese--diet and exercise, even in combination with drug therapy, are usually not enough to achieve adequate weight loss.^1-4 There is growing consensus that bariatric surgery is the most effective intervention for achieving sustained weight loss in the obese population.^3-11 In addition, emerging evidence suggests that bariatric surgery is cost effective from an overall, long-term health care standpoint, compared with medical management.^10,12 However, because of the serious risks associated with it, bariatric surgery is recommended only for morbidly obese individuals who have not responded to diet, exercise, and/or medications.^1-3 For people with less severe obesity, the risks of bariatric surgery typically outweigh the potential benefits.^7,13

In the United States, the number of bariatric surgery procedures has increased significantly over the past few decades.^1,14,15 More than 140,000 people had bariatric surgery in 2005, compared with approximately 13,000 patients in 1998. This represents a 1,000% increase between the years 1998 and 2005.^3,5 Data suggest that the use of bariatric surgery to control weight is likely to continue increasing over the next decade.¹⁴ For this reason, pharmacists will be called upon more often to provide services to patients who have had bariatric surgery.⁴ 

Obesity Epidemic
Obesity--defined as a body mass index (BMI) of greater than 30 kg/m²--is a chronic medical condition that is increasing in epidemic proportions in the U.S. ^{3,5,6,8,11,14-20} Table 1 defines obesity classes according to BMI. ^2,8,11,18 Obesity has become a major health problem in the U.S. due to its high prevalence, causal relationship with serious medical comorbidities ( Table 2), and economic consequences.^5,15,21,22 The percentage of obese American adults increased from 15.3% in 1995 to 23.9% in 2005.¹⁶ Today, more than 31% of American adults (~61 million people) are obese. ^5,8 Of these, about 4.8% are considered to be morbidly obese.¹⁶

Obesity, particularly abdominal obesity, is associated with an increased risk of type 2 diabetes, hyperlipidemia, hypertension, obstructive sleep apnea, coronary heart disease, and stroke.^{9,11,12,16,17,23} In the U.S., health care expenditures related to obesity and obesity comorbidities amount to $100 billion annually. Each year, there are 400,000 deaths attributed to obesity in the U.S. ^16,24 The life expectancy of an obese individual is profoundly shorter than that of a normal-weight individual--for example, a 25-year-old morbidly obese male has a 22% reduction in expected remaining lifespan, representing an approximate loss of 12 years of life.¹⁷

Clinical Guidelines
Most clinical guidelines regarding the role of bariatric surgery have followed the lead of the 1991 NIH Health Consensus Development Conference by concluding that such procedures should be considered for patients with either a BMI of greater than 40 kg/m² or a BMI of greater than 35 kg/m² with coexisting medical conditions.^6,9,11,14-16 These criteria are endorsed by the National Heart, Lung, and Blood Institute guidelines for the treatment of obesity, published in 1998. The criteria are also endorsed in more recent guidelines published by the Institute for Clinical Systems Improvement, the American Society for Bariatric Surgery, and the European Association for Endoscopic Surgery.¹⁶ The American College of Physicians has adopted a somewhat more conservative approach (Table 3), recommending that bariatric surgery be considered only in patients who have a BMI of 40 kg/m² or greater as well as coexisting medical conditions. ^16,25,26 In general, each of these guidelines recommends that patients who are considering bariatric surgery attempt to lose weight prior to surgery, be free of medical and psychological complications, and be cared for by a multispecialty team with experience in bariatric surgery and perioperative care.¹⁶

Types of Procedures
Bariatric surgery procedures can be categorized into operations utilizing one of three methods to produce weight loss: malabsorptive, restrictive, and mixed technologies. ^3,11 Table 4 compares and contrasts the three most commonly used contemporary bariatric surgery procedures: biliopancreatic diversion, gastric banding, and gastric bypass.^{2,3,7-9,11,24}

Malabsorptive Procedures: Malabsorptive procedures decrease the effectiveness of nutrient absorption by shortening the length of the functional small intestine. Profound weight loss can be achieved depending on the length of the functional small bowel segment. However, the benefit of superior weight loss is often offset by significant metabolic complications, such as protein calorie malnutrition and various micronutrient deficiencies.⁸ Although rarely used today, biliopancreatic diversion with or without duodenal switch is a classic example of a strictly malabsorptive procedure.⁷

Biliopancreatic diversion with or without duodenal switch involves removing part of the stomach.^2,7 The remaining section is surgically connected to the lower part of the small intestine. Weight loss occurs primarily because the contents of the stomach bypass the majority of the small intestine, thereby passing into the large intestine before most of the nutrients and calories can be absorbed.⁷ Inevitable complications associated with this procedure include malabsorption of carbohydrates, proteins, lipids, minerals, and vitamins. Other complications include diarrhea, gallstones, hepatic cirrhosis, osteoporosis, osteomalacia, neuropathy, and night blindness associated with mineral and vitamin deficiencies. This procedure is rarely performed in the U.S.²

Restrictive Procedures: Restrictive procedures limit caloric intake by downsizing the stomach's reservoir capacity. They limit solid food intake by restriction of stomach size (the only mechanism of action), leaving the absorptive function of the small intestine intact. Although these procedures are simpler in comparison to malabsorptive procedures, they tend to produce more gradual weight loss. Gastric banding is the most commonly performed restrictive procedure.^2,8

Gastric banding, which can now be performed laparoscopically, limits food intake by placing a constricting ring completely around the top end of the stomach.² The band is connected to a narrow tube that extends to an access port just beneath the skin; a health care provider can narrow or widen the entrance to the stomach by injection or removal of saline through the port. Passing of food from the upper pouch to the rest of the stomach is delayed, and the patient feels full after eating less. Gastric banding is a popular choice of weight-loss surgery, because it is relatively simple to perform, can be adjusted or removed, and has a low complication rate. Reported effectiveness of this procedure varies, with loss of excess weight ranging from 45% to 75% after two years.⁷ Band-related complications include splenic injury, esophageal injury, wound infection, band slippage, reservoir deflation/leak, persistent vomiting, and gastrointestinal reflux disease.^2,9,24

Mixed Procedures: These procedures limit food intake while decreasing absorption of nutrients within the body.^7,8 Gastric bypass, also known as Roux-en-Y gastric bypass, is the most common mixed surgical procedure used to treat weight loss in the U.S.⁷ Gastric bypass combines restriction and malabsorption techniques, creating both a small gastric pouch and a bypass that prevents patients from absorbing all they have eaten.² Roux-en-Y gastric bypass, which has a high success rate, is considered the gold standard among bariatric procedures. It can be performed as open surgery or laparoscopically; the laparoscopic procedure is preferred, if possible, because patients who undergo this procedure typically require less time to recover and have fewer complications.^6,11,27

Approximately 80% of gastric bypass patients experience a 60% to 80% loss of excess weight in the first year, with long-term stabilization at 50% to 60% loss of excess body weight (defined as a BMIof >25 kg/m² or body weight that exceeds the ideal BMI).^3,28 Generally speaking, weight loss plateaus after one to two years.⁷ Complications associated with gastric bypass include leaks at the junction of the stomach and small intestine, acute gastric dilation, vomiting, wound hernias, intestinal obstruction, anemia, vitamin and mineral deficiencies, and dumping syndrome.²

Outcomes of Bariatric Surgery
Numerous studies have demonstrated that bariatric surgery reduces weight up to six times more than lifestyle modifications and/or diet.¹³ There are other advantages to bariatric surgery aside from the dramatic weight loss; published estimates of the impact of weight loss on cardiovascular disease and diabetes suggest that substantial benefits are produced by weight loss (Table 5). ² Data also suggest that compared with controls, patients who underwent bariatric surgery experienced a significant relative risk reduction of cancer (76%), endocrine disease (65%), infectious disease (77%), musculoskeletal problems (59%), nervous system disease (39%), respiratory conditions (76%), and psychiatric and mental health problems (47%).³

Complications of Bariatric Procedures
In several large-scale studies, the mortality rate associated with bariatric surgery was 0.1% to 2%. Common causes of death included pulmonary embolism and serious surgical complications.¹⁵ Identified factors that may increase mortality include lack of experience by the surgeon, advancing patient age, male sex, severe obesity (BMI ?50 kg/m²), and coexisting medical conditions.^3,8,16

Common nonfatal perioperative complications following bariatric surgery include venous thromboembolism, anastomotic leaks, wound infections, bleeding, incidental splenectomy, incisional and internal hernias, and early small-bowel obstruction.¹⁶ In the only large, well-controlled, prospective study of bariatric surgery--the Swedish Obese Subjects (SOS) trial--postoperative complications occurred in 13% of patients. Of these patients, 0.5% experienced bleeding, 0.8% experienced embolism or thrombosis, 1.8% had wound complications, and 6.1% had pulmonary complications.^16,29

Rapid weight loss is a known cause of gallstones. An estimated 30% of patients who have gastric bypass develop cholelithiasis; routine oral bile salt administration has been shown to substantially decrease the frequency of this complication. As a result, most bariatric surgery programs advise bile salt supplementation for the first six months following gastric bypass.³

Complications from bariatric surgery may require subsequent readmission or reoperation.¹⁶ Data suggests that 6% to 9% of patients require additional surgeries to correct complications associated with bariatric surgery. The most common reasons for the additional surgeries include gastric revision and hernia repair.⁸

Dumping Syndrome: Postoperative gastrointestinal complications of bariatric surgery are common. Nausea and vomiting frequently occur in more than 50% to 70% of patients undergoing restrictive procedures, partly as a result of eating too much or eating too rapidly. The dumping syndrome--a complex of neurohormonally mediated symptoms such as facial flushing, lightheadedness, palpitations, fatigue, and diarrhea--occurs in more than 50% of patients after Roux-en-Y gastric bypass when they consume meals high in refined sugars or fats.^12,16 The same phenomenon does not appear to happen after gastric banding procedures. ²⁰ Dumping syndrome may discourage patients from eating foods with a high sugar content, thus contributing to the beneficial effects of the surgery. ¹⁶ Patients who develop dumping syndrome should be advised to avoid foods that provoke symptoms. Dumping syndrome is rarely severe enough to cause significant problems with nutritional intake.²⁰

Dietary Considerations Following Surgery
In the immediate postoperative period, bariatric surgery patients require a water and sugar-free, clear-liquid diet. At one day to two weeks, patients can usually progress to high-protein liquid diets with products such as Boost HP, Ensure Plus, and Carnation Instant Breakfast. At about two to four weeks following surgery, most patients can tolerate pureed diets (e.g., yogurt, soups, cottage cheese, eggs, protein shakes, and soft vegetables). Patients should generally eat about 3 oz. four to six times per day; drink water and sugar-free, clear liquids; stop eating if they feel full; and avoid consuming foods and beverages at the same time (i.e., patients should drink beverages 30 minutes before or 60 minutes after eating). At around four to six weeks, diets are usually advanced, including sliced deli meat, cheeses, salads, soups, and fruits, in addition to the pureed diet. Patients should be encouraged to slowly add new foods one at a time in small quantities during this transition. The stomach begins to tolerate larger quantities of food during this period. Finally, after six weeks, diets should be advanced to include solid foods at each meal. However, certain foods (e.g., red meats, corn, rice, breads, fruits with seeds, high-fat foods) often cause vomiting and should be avoided. Additionally, overeating can cause vomiting and result in electrolyte imbalances. Clinical dietitians are frequently consulted to recommend patient-specific diets that maximize calories and prevent dehydration and electrolyte imbalances.²⁰

Nutritional Deficiencies
Nutritional deficiencies commonly occur in patients who have undergone bariatric surgery due to inadequate intake of nutrients and alterations in the digestive anatomy as a result of surgery.²² It is important to note that nutritional deficiencies are much more common in patients who have had gastric bypass than in patients who have had solely restrictive procedures, since restrictive procedures retain use of the entire gastrointestinal tract.²² Iron deficiency is the most commonly recognized micronutrient deficiency following gastric bypass.³ Data suggest that up to 50% of patients suffer from iron deficiency following gastric bypass.⁸ Patients also commonly experience deficiencies in the fat-soluble vitamins (i.e., vitamins A, D, E, and K).²² Calcium and vitamin D absorption are also decreased and can lead to hyperparathyroidism. Many patients who have undergone bariatric surgery experience vitamin B₁₂ deficiency secondary to decreased intrinsic factor.⁸ Likewise, thiamine deficiency has been reported in patients who experience recurrent vomiting. ²⁰ 

In order to prevent nutritional deficiencies, bariatric surgery patients require vitamin and mineral supplements. Table 6 lists general guidelines for administering these supplements in patients who have had bariatric surgery.^3,8,20,22,30 Patients should generally have serum iron, hematocrit, 25-hydroxy-vitamin D, parathyroid hormone, and vitamin B₁₂ levels monitored at six-month intervals until stable on replacement therapies; levels should then be monitored yearly. In addition, bone density should be monitored every one to two years. Vitamin A should be monitored yearly in all patients who have had malabsorptive procedures.³⁰

Special Populations
Pregnancy: Data suggest that weight loss after bariatric surgery may lead to increased fertility, and this can lead to unwanted pregnancies. Pharmacists should encourage all sexually active women who have undergone bariatric surgery to use a backup form of contraception.²² In addition, pharmacists should inform patients and prescribers that low-dose oral contraceptive products may have decreased absorption in patients who have had bariatric surgery.³¹

Bariatric surgery does not appear to be associated with adverse perinatal outcomes, and pregnancy after surgery may be less likely to be complicated by gestational diabetes, hypertension, and macrosomia.²⁰ The American College of Obstetricians and Gynecologists (ACOG) recommends that women delay pregnancy for 12 to 18 months after having bariatric surgery and be evaluated for nutritional deficiencies. For women who have had gastric banding, the ACOG recommends that the band be monitored during pregnancy and adjusted accordingly.^20,32

Pediatrics: Between 1980 and 2002, the prevalence of obesity tripled in children and adolescents age 6 to 19 years.³³ More recent data suggest that one million adolescents between the age of 12 and 19 years are obese.¹⁵ Perhaps more alarming is the fact that obesity-related comorbid diseases are as prevalent and severe among adolescents as among adults. Specifically, dramatic increases in the incidence of obesity-related glucose intolerance/diabetes, metabolic syndrome, premature coronary artery disease and stroke, and impaired quality of life all indicate that severe obesity constitutes a major health problem for adolescents and adults. Limited early experience with bariatric surgery in adolescents suggests that the surgery is safe and is associated with weight loss, correction of obesity comorbidities, and improved self-image and socialization.³ However, many experts feel that adolescent patients may not have proper insight to appreciate the consequences of undergoing surgery or to cooperate fully with follow-up care. ¹⁶

Role of the Pharmacist
It is important for all pharmacists who take care of patients who have had bariatric surgery to monitor patient profiles regarding appropriateness of therapy and to have a basic understanding of bariatric dosing considerations.³⁴ This knowledge can greatly benefit patients who have had any of the contemporary procedures.^1,4,34

Decreased Medication Requirements: Many chronic medical conditions improve quickly during the immediate postoperative period, necessitating medication changes. Blood pressure, which often decreases to the normal range without continued therapy, should be monitored at all postoperative visits. It is important to note that hypotension is common in the early postoperative period, especially in the presence of persistent vomiting and poor fluid intake. Patients should be monitored monthly until blood pressure stabilizes, and antihypertensive medications should be adjusted accordingly.²⁰

Blood glucose should also be monitored frequently in the early postoperative period, and patients should be managed with sliding-scale insulin. Many patients with diabetes have a decreased need for insulin after bariatric surgery. Discontinuation of all diabetic medications should be considered when blood glucose normalizes and after the patient begins to eat.²⁰

Generally, medications for gastrointestinal reflux should be discontinued after bariatric surgery, since obesity is one of the primary causes of gastrointestinal reflux. Medications can be restarted if symptoms recur.²⁰

It is generally ill advised to decrease or stop psychiatric medications during the immediate postoperative period. Maintaining patients on psychiatric medications reduces emotional lability, which is common during the first few months after bariatric surgery. ²⁰

Bariatric Dosing Considerations: The reduced size of the stomach after surgery can place patients at risk for gastrointestinal adverse events; therefore, patients should be instructed to avoid using nonsteroidal anti-inflammatory drugs and salicylates. Pharmacists should explain that other options for pain relief exist, including acetaminophen, opioids, and tramadol. Bisphosphonates should be avoided, since they too may increase the risk of gastrointestinal ulcerations. Because patients who have bariatric surgery can be at risk for osteoporosis due to decreased calcium absorption, other treatment options (e.g., calcitonin nasal spray, synthetic parathyroid hormone, or raloxifene) should be considered. Finally, patients should be instructed to avoid oral corticosteroids, medicinal caffeine, and liquid medications that contain more than 2 g of sugar, because these too can increase the risk of gastrointestinal problems. ²²

Decreased intestinal length and surface area in patients who have had gastric bypass can lead to the reduced absorption of extended-release, delayed-release, and enteric- or film-coated product formulations. To overcome this problem, the immediate-release dosage forms should be substituted, which usually requires increased frequency of administration.²² In addition, drugs that are rapidly and primarily absorbed in the stomach or duodenum are likely to exhibit decreased absorption in patients who have had gastric bypass (Table 7).^22,31,34

Special considerations also exist regarding the administration of total parenteral nutrition to patients who have had bariatric surgery.³⁴ Bariatric surgery patients who have been receiving nothing orally or who have been on clear liquids prior to initiation of nutritional support are at an increased risk for developing refeeding syndrome.³⁵ The syndrome is primarily associated with hypophosphatemia, as well as declines in serum potassium magnesium and calcium levels. In rare occurrences, cardiac dysfunction and fluid retention also occur. The mechanism of these electrolyte abnormalities can be explained by the acute administration of macronutrients (primarily dextrose) that promote anabolism (muscle building) in a state of overall depleted electrolyte body stores (due to postoperative malnourishment). Consequently, carbohydrates and lipids should generally be dosed lower than the amount needed to maintain current weight, while protein should be dosed higher in order to avoid muscle catabolism.³⁴

Conclusion
As the number of patients undergoing bariatric surgery increases, patient populations who have had the procedures and present to ambulatory care and hospital pharmacists will also increase. Accordingly, it is imperative for all clinicians to be familiar and comfortable with the medication management of these patients. Clinicians must not only understand the physiologic, metabolic, and psychological manifestations of morbid obesity but also be cognizant of the predicted improvement in comorbidities and the potential complications that can occur in patients who undergo bariatric surgery.²⁰ Clearly, pharmacists have a vital role, as part of a multidisciplinary team, in providing bariatric patients with appropriate medical care.³⁴

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