How does gastric bypass surgery achieve weight loss? Surgical principles and long-term effects explained.

Gastric Bypass:

Scopinaro first used Billroth II gastrectomy for the treatment of obesity with good results. Gastric bypass, also known as RouxY gastric bypass, involves creating a 20-30 ml gastric pouch at the fundus of the stomach. The proximal end of the RouxY jejunum is anastomosed to this pouch, and a jejunostomy is performed 40-60 cm below it. Gastric bypass not only restricts food intake but also induces dumping syndrome after carbohydrate consumption, further limiting the eating habits of patients with hyperphagia, thus making weight loss more effective and lasting.

1. Surgical Procedure: A midline incision is made in the upper abdomen. The abdominal cavity is exposed using a Gomez retractor. An 18-gauge nasogastric tube is placed. Using your index finger, enter the esophagus and stomach posterior to the cardia on the left side of the esophagus, and dissect downwards and to the right. At the bifurcation of the descending branch of the left gastric artery, approximately 2.5–3.0 cm below the esophageal junction, extend your index finger.

2. Surgical Outcomes
Within one year post-surgery, significant weight loss is observed. For 2–3 years post-surgery, weight is maintained at 30% above the standard weight. If morbid obesity is defined as exceeding the standard weight by 45 kg, 94% of patients are no longer morbidly obese within two years post-surgery.

Gastric bypass surgery can achieve relatively lasting and effective weight loss without serious metabolic disorders. According to Brolin, 91% of patients experienced the disappearance or remission of obesity-related comorbidities within two years.

Morbid obesity is often associated with abnormal glucose metabolism. According to Pories, approximately 21% of morbidly obese patients have type 2 diabetes, and 13% have impaired glucose tolerance. Of these diabetic patients, 95% underwent gastric bypass surgery and achieved normal glucose metabolism and blood glucose levels; some patients even experienced improved glucose tolerance post-surgery and were able to discontinue insulin. The significant improvement in diabetic patients was not only due to weight loss or reduced calorie intake, but also likely due to the role of the neuroendocrine bypass in the gastric antrum and duodenum.

Post-gastric bypass surgery, 90% of morbidly obese patients with sleep apnea and pulmonary insufficiency experienced symptom improvement, such as increased PaO₂, decreased PaCO₂, and a reduction in the frequency of sleep apnea.

Furthermore, with significant post-operative weight loss, chronic pain associated with obesity and musculoskeletal weakness caused by degenerative arthritis also showed significant improvement.

3. Complications Due to difficulties in intraoperative exposure, hepatomegaly caused by hepatic steatosis, short mesentery, and thickened greater omentum in morbidly obese patients, early postoperative complications are prone to occur.

(1) Short-term complications of gastric bypass surgery

① Mortality: The mortality rate among short-term complications of gastric bypass surgery is approximately 1.5%. These patients typically have pre-existing high-risk factors, such as Pickwickian syndrome, uncontrolled diabetes, cardiopulmonary failure, and debilitating arthritis.

② Wound infection: Wound problems are the most common. Approximately 10% of patients experience small-scale wound infection, 10% experience seroma and fat liquefaction, 3.8% experience severe wound infection, and 1% experience wound dehiscence. 2.5% of patients develop anastomotic leakage or subseptal abscess. Infection is most common in patients with diabetes.

(2) Long-term complications of gastric bypass surgery

① Dumping syndrome: Approximately 70% of patients experience post-operative nausea, weakness, sweating, palpitations, and syncope. However, this is a desirable outcome after surgery because these symptoms alter patients' eating habits, directly impacting the effectiveness of long-term weight control.

② Nutritional Deficiencies

Reports indicate that during the early postoperative period of significant weight loss, 49% of patients experienced hair loss, 43% experienced constipation, 43% experienced anemia, 37% experienced vitamin B₁₂ deficiency, and 30% experienced folic acid deficiency. These nutritional deficiencies occur because rapid weight loss leads to a decline in nutrient and protein levels. To avoid nutritional deficiencies, detailed monitoring of nutrition and metabolism is necessary before and after surgery; during the perioperative period, a balanced nutritional supply should be ensured, and relevant nutrients may be supplemented as needed.

③ Nausea and Vomiting

Approximately 35% of patients experience nausea and vomiting, mostly due to overeating in the early postoperative period.

④ Other complications: 16% developed incisional hernia; 12% developed neuropathy, caused by insufficient intake of B vitamins, which needs to be corrected promptly; 9% developed cholecystitis; 6% developed bile reflux and esophagitis; 4% developed small bowel obstruction due to intestinal adhesions; 3.8% developed anastomotic ulceration; 3% developed gastric sac dilatation; 2.8% experienced anastomotic staple dislodgement; 1.3% experienced anastomotic stenosis. If gastric sac dilatation, an overly large anastomosis, or anastomotic staple dislodgement occurs, reoperation for repair is often necessary.