CHAPTER 9 Gastric Bypass
INDICATIONS FOR SURGERY
Obesity: The specific indications for bariatric surgery continue to evolve. The National Institutes of Health issued a consensus statement in 1991 that established guidelines for identifying patients for whom the benefits of surgery outweigh the associated risks (Box 9-1). Importantly, patients weighing more than 600 pounds exceed the maximum weight capacity of many operating tables and may require staged therapy (including dietary modification) before a definitive surgery.
PREOPERATIVE EVALUATION
I. Cardiovascular: A preoperative electrocardiogram should be obtained for men older than 40 years, women older than 50 years, or patients with known coronary artery disease, diabetes mellitus, hypertension, obstructive sleep apnea, or arrhythmias. Patients with multiple cardiac risk factors should also undergo stress testing when possible. Unfortunately, this is not always feasible because most patients cannot tolerate even moderate exercise and thallium stress testing is inaccurate in patients with a BMI of more than 30. When available, transesophageal dobutamine stress echocardiogram is often the optimal study. In patients found to be at moderate or high cardiovascular risk, perioperative β-blockade may be recommended, although no study has yet demonstrated a benefit in this population.
II. Pulmonary: Between 40% and 80% of patients undergoing bariatric surgery have obstructive sleep apnea. Generally, patients should undergo preoperative sleep studies. If obstructive sleep apnea is shown, 4 weeks of CPAP or bilevel positive airway pressure (biPAP) is required before surgery. Long-standing OSA or reactive airway disease (also associated with obesity) can lead to pulmonary hypertension, which substantially increases operative risk. Systolic pulmonary artery pressures of greater than 50 mm Hg are a contraindication to surgery.
III. Psychiatric: More than 50% of candidates for bariatric surgery take psychotropic medication, most often for depression. The presence of inadequately treated psychiatric conditions has been correlated with inadequate weight loss and dissatisfaction after surgery. A structured interview with a psychologist or psychiatrist using a validated questionnaire, such as the Weight and Lifestyle Inventory or the Beck Depression Inventory, is recommended.
IV. Gastrointestinal: Nonalcoholic steatohepatitis (NASH) and cirrhosis are present in 40% and 2% of the severely obese population, respectively. Hepatic compromise is a contraindication to surgery, and liver function tests should, therefore, be obtained for all surgical candidates. Because of the high rate of postoperative cholelithiasis, some surgeons advocate screening for gallstones with a right upper quadrant ultrasound and, if the study is positive, removal of the gallbladder at the time of bariatric surgery.
V. Educational: Bariatric surgery results in the loss of 60% of excess body weight in most individuals, but requires extensive lifestyle changes postoperatively. Many patients have unrealistic expectations and require preoperative education. Postoperative referral to a support group may also be beneficial.
COMPONENTS OF THE PROCEDURE AND APPLIED ANATOMY
Preoperative Considerations
I. Sequential compression devices should be applied before the induction of anesthesia to prevent deep vein thrombosis (DVT). Some centers advocate preoperative treatment with subcutaneous heparin as well.
II. More than 50% of obese patients have gastroesophageal reflux disease. Supine positioning increases intra-abdominal pressure and the risk of aspiration during intubation. Intubation with the head of the table elevated at 15 degrees to 20 degrees is often preferred to decrease this risk.
Patient Positioning and Preparation
I. The patient is placed in the supine position with the arms extended. Pressure points are padded to prevent necrosis. Additionally, buttresses are constructed under the arms to minimize the amount of traction placed on the torso and to decrease the risk of brachial plexopathies.
II. The sterile preparation should extend to the nipples superiorly, to the pubis inferiorly, and to the posterior axillary lines laterally.
