Special Surgery 34. Bariatric Surgery

I. Definition, Indications and Patient Selection

Definition

Bariatric/metabolic surgery = surgical treatment of obesity aiming at durable weight loss and improvement/remission of obesity-related comorbidities
Mechanisms:

Restricts food intake
Changes gut hormones and bile acid/metabolic signaling
May reduce nutrient absorption depending on procedure
Improves insulin sensitivity and beta-cell function, especially in type 2 diabetes

Modern term "metabolic surgery" emphasizes comorbidity improvement, not only weight loss

Obesity-Related Comorbidities

Type 2 diabetes mellitus
Hypertension
Obstructive sleep apnea
Dyslipidemia
NAFLD / NASH / metabolic dysfunction-associated steatotic liver disease
GERD
Polycystic ovary syndrome, infertility
Osteoarthritis
Cardiovascular disease risk
Reduced quality of life and functional limitation

Indications

Classic exam/NIH-style thresholds:

BMI >=40 kg/m2 regardless of comorbidities
BMI >=35 kg/m2 with at least one serious obesity-related comorbidity
BMI >=30 kg/m2 can be considered in selected patients with uncontrolled type 2 diabetes/metabolic disease

Current ASMBS/IFSO-style framing:

Metabolic and bariatric surgery is recommended for BMI >35 kg/m2 regardless of comorbidity presence/severity
Should be considered for BMI 30-34.9 kg/m2 with metabolic disease
Asian populations use lower BMI thresholds because metabolic risk occurs at lower BMI
Appropriately selected adolescents may be candidates in specialist centers

Additional Requirements

Multidisciplinary assessment:

Bariatric surgeon
Dietitian/nutrition specialist
Psychologist/psychiatrist when indicated
Anesthesiology and internal medicine/endocrinology assessment

Previous non-surgical therapy attempted or insufficient durable response:

Diet, exercise, behavioral therapy
Anti-obesity medication when appropriate

Patient understands procedure, risks, lifestyle changes and lifelong follow-up
Ability to comply with supplementation and monitoring

Contraindications / Relative Contraindications

Uncontrolled psychiatric illness
Active alcohol/drug abuse
Untreated eating disorder with unsafe behavior
Inability to understand or comply with postoperative care
Prohibitive anesthetic/surgical risk
Pregnancy: delay surgery; avoid pregnancy during rapid weight-loss period after surgery
Untreated endocrine cause of obesity should be evaluated

Preoperative Workup

History/physical exam with obesity complications assessment
Labs:

CBC, electrolytes, renal/liver function
HbA1c/glucose/lipids
Iron/ferritin, B12, folate
Vitamin D, calcium, PTH if indicated

Screen/treat sleep apnea
Upper endoscopy depending on symptoms/local practice/procedure choice, especially GERD before sleeve
Abdominal US if gallstone symptoms or local protocol
Smoking cessation and VTE risk assessment
Preoperative low-calorie/liver-shrinking diet often used

II. Types of Bariatric Surgery

1. Sleeve Gastrectomy (SG)

Most commonly performed bariatric operation worldwide
Restrictive + hormonal/metabolic procedure
About 70-80% of greater curvature stomach removed
Narrow tubular gastric sleeve remains
Mechanism:

Reduced gastric volume → early satiety
Reduced ghrelin-producing fundus → less hunger
Accelerated gastric emptying and gut hormone changes

Pros:

Technically simpler than bypass
No intestinal anastomosis
No internal hernia from mesenteric defects
Good weight loss and diabetes improvement

Cons:

Irreversible gastric resection
Staple-line leak/bleeding risk
Can worsen or cause GERD
May be less effective than bypass/duodenal switch for severe reflux or very severe metabolic disease

2. Roux-en-Y Gastric Bypass (RYGB)

Restrictive + mild malabsorptive + strong metabolic procedure
Creates small gastric pouch
Pouch anastomosed to jejunum as alimentary limb
Bypasses most stomach, duodenum and proximal jejunum
Biliopancreatic limb carries bile/pancreatic juice and joins alimentary limb distally

Pros:

Excellent durable weight loss
Strong type 2 diabetes remission/improvement
Often improves GERD
Long clinical experience

Cons:

More complex than sleeve
Anastomotic leak/stricture risk
Internal hernia risk through mesenteric defects
Marginal ulcers
Dumping syndrome
Nutritional deficiencies: iron, B12, folate, calcium, vitamin D

3. Biliopancreatic Diversion with Duodenal Switch (BPD/DS)

Sleeve gastrectomy + long small bowel bypass
Most powerful weight-loss/metabolic operation
Useful in selected patients with very severe obesity or severe metabolic disease
Highest nutritional risk:

Protein-calorie malnutrition
Fat-soluble vitamin deficiency: A, D, E, K
Mineral deficiency
Diarrhea/steatorrhea

Requires highly compliant patient and specialist long-term follow-up

4. One-Anastomosis Gastric Bypass (OAGB / Mini-Gastric Bypass)

Long gastric pouch with loop gastrojejunostomy
Restrictive + malabsorptive/metabolic
Technically simpler than RYGB in some hands
Concerns: bile reflux, marginal ulcer, nutritional deficiencies
Used in selected centers; local practice varies

5. Adjustable Gastric Band

Pure restrictive operation with band around proximal stomach
Now much less common because of inferior long-term weight loss and reoperation/removal risk
Complications: slippage, erosion, dysphagia, esophageal dilation, port problems

Procedure Choice

Clinical situation	Often favored procedure logic
Severe GERD / Barrett esophagus	RYGB often favored; sleeve may worsen reflux
Very high BMI / severe diabetes	RYGB or BPD/DS considered depending on risk/compliance
Need simpler operation / avoid bowel bypass	Sleeve gastrectomy often chosen
High nutritional non-adherence risk	Avoid highly malabsorptive procedures
Previous abdominal surgery	Individualized; adhesions may influence approach

III. Outcomes, Complications and Management

Expected Outcomes and Benefits

Sustained weight loss, commonly about 25-35% of initial body weight depending on procedure and adherence
Type 2 diabetes improvement or remission
Improved hypertension
Improved dyslipidemia
Improved obstructive sleep apnea
Improved NAFLD/NASH in many patients
Improved mobility, fertility/PCOS, quality of life
Reduced long-term mortality in appropriate patients compared with non-operative management

Early Complications

Bleeding:

Intraluminal or intra-abdominal
Tachycardia, Hb drop, melena/hematemesis or drain blood

Staple-line/anastomotic leak:

Most feared early complication
Signs: tachycardia, fever, abdominal/shoulder pain, sepsis
Diagnosis: CT with oral/IV contrast, clinical suspicion more important than negative imaging
Treatment: antibiotics, drainage, endoscopy/stent/vacuum therapy or surgery depending on severity

DVT/PE:

Obesity increases VTE risk
Prevention: early mobilization, pneumatic compression, pharmacologic prophylaxis

Wound infection, pneumonia, atelectasis
Anastomotic edema/early obstruction

Late Complications

Nutritional deficiencies:

Iron deficiency anemia
Vitamin B12 deficiency
Folate deficiency
Calcium/vitamin D deficiency → secondary hyperparathyroidism, bone loss
Thiamine deficiency with vomiting → Wernicke encephalopathy risk
Fat-soluble vitamins A/D/E/K especially after BPD/DS

Dumping syndrome after RYGB:

Early: tachycardia, sweating, cramps, diarrhea after sugar-rich meal
Late: postprandial hypoglycemia
Treatment: diet first, small meals, avoid simple sugars

Marginal ulcer after RYGB/OAGB:

Risk: smoking, NSAIDs, H. pylori, ischemia
Treatment: PPI, stop NSAIDs/smoking, endoscopy if symptoms/bleeding

Internal hernia after RYGB:

Intermittent postprandial abdominal pain, nausea/vomiting
Can cause closed-loop obstruction/ischemia
Low threshold for CT and diagnostic laparoscopy

GERD after sleeve gastrectomy
Gallstones due to rapid weight loss
Weight regain / insufficient weight loss
Excess skin, body contouring needs
Alcohol-use disorder risk can increase after bypass in some patients

Emergency Red Flags After Bariatric Surgery

Persistent tachycardia after operation
Fever/sepsis
Severe abdominal pain with minimal findings
Vomiting/inability to tolerate liquids
GI bleeding
Dyspnea/chest pain → PE until excluded
Post-RYGB colicky intermittent pain → internal hernia until excluded

IV. Follow-Up, Nutrition and Practical Exam Points

Lifelong Follow-Up

Requires lifelong multidisciplinary follow-up:

Surgeon/bariatric team
Dietitian
Primary care/endocrinology
Psychology/psychiatry when needed

Monitor weight trajectory, comorbidities, eating behavior and mental health
Adjust diabetes, blood pressure and lipid medications after weight loss
Pregnancy should usually be delayed until weight stabilizes, often 12-18 months

Nutrition Principles

Diet progression: liquids → pureed/soft → solid high-protein diet
Small frequent meals, slow eating, chew well
Protein priority
Avoid high-sugar liquids/foods, especially after bypass
Avoid dehydration; drink between meals rather than with meals if symptomatic
Alcohol caution
Avoid NSAIDs especially after RYGB because marginal ulcer risk

Routine Supplementation

Daily bariatric multivitamin/mineral preparation
Vitamin B12
Iron, especially menstruating women and bypass/DS patients
Folate
Calcium citrate + vitamin D
Thiamine urgently if prolonged vomiting or poor intake
Fat-soluble vitamins A/D/E/K and protein monitoring especially after BPD/DS

Laboratory Monitoring

CBC
Iron studies/ferritin
B12, folate
Vitamin D, calcium, PTH
Albumin/protein status in malabsorptive procedures
Liver/kidney function
Glucose/HbA1c, lipids
Additional vitamins/minerals according to procedure and symptoms

Comparison Summary

Procedure	Mechanism	Main advantage	Main concern
Sleeve gastrectomy	Restriction + hormonal	Common, simpler, no bypass	GERD, irreversible, leak
RYGB	Restriction + mild malabsorption + metabolic	Diabetes/GERD benefit, strong weight loss	Internal hernia, dumping, deficiencies
BPD/DS	Restriction + marked malabsorption	Strongest weight/metabolic effect	Highest nutritional/protein deficiency risk
Gastric band	Restriction	Reversible	Less used; slippage/erosion/reoperation

Exam-Focused Algorithm

Assess BMI + comorbidities + previous conservative treatment
Exclude contraindications and perform multidisciplinary assessment
Choose procedure based on GERD, diabetes, BMI, nutrition risk and patient factors
Operate laparoscopically in most elective cases
Prevent early complications: leak, bleeding, VTE
Ensure lifelong vitamins, labs and follow-up

Exam focus: Sleeve is common and simpler but may worsen GERD. RYGB is metabolically strong and improves reflux but has internal hernia, dumping and deficiency risks. BPD/DS has the strongest effect but the highest nutritional risk. Bariatric surgery is not just an operation: patient selection and lifelong follow-up are mandatory.