Indications for and complications of bariatric surgery

Procedures - the distinction that drives everything

Type	Procedure	Mechanism
Restrictive	Sleeve gastrectomy (now the commonest in Australia), adjustable gastric band (largely abandoned)	Reduced volume; sleeve also removes the ghrelin-producing fundus
Restrictive + malabsorptive	Roux-en-Y gastric bypass (RYGB)	Small pouch + BYPASSES duodenum and proximal jejunum
Predominantly malabsorptive	Biliopancreatic diversion +/- duodenal switch	Most weight loss, most severe nutritional consequences

*The key fact: the duodenum and proximal jejunum are the principal site of IRON and CALCIUM absorption* - bypass them and you buy iron deficiency and osteoporosis
Weight loss is largely NOT mechanical - inc GLP-1 and PYY, dec ghrelin, altered bile acid signalling and microbiome

~30-35% of Australian adults obese; ~25,000-30,000 bariatric procedures/yr, >90% in the private sector
F>M ~4:1
Excess weight loss: sleeve ~55-60%, RYGB ~65-70%, BPD ~75% at 2 years
Total body weight loss ~25-30% (RYGB), ~20-25% (sleeve); ~20-30% regain significant weight by 10 years
T2DM remission ~60-80% at 2 years (RYGB > sleeve); ~35-50% relapse by 5-10 years
Perioperative mortality ~0.1-0.3% - comparable to laparoscopic cholecystectomy

Restriction - reduced gastric capacity, early satiety
Neurohormonal (dominant)
- dec ghrelin (fundal resection in sleeve)
- inc GLP-1 and PYY from rapid nutrient delivery to the distal small bowel -> satiety, inc insulin secretion
- Glycaemic improvement begins within DAYS, before meaningful weight loss - proving the hormonal mechanism
Malabsorption - shortened absorptive length, bile/food separation
Bile acid and microbiome shifts - FXR/TGR5 signalling

BMI >=40, OR
BMI >=35 with a weight-related comorbidity (T2DM, OSA, hypertension, MASLD, osteoarthritis, PCOS, GORD)
BMI >=30 with poorly controlled T2DM (metabolic surgery)
Lower thresholds by 2.5 kg/m2 in people of Asian ancestry
After a documented trial of supervised non-surgical management (though evidence does not require failure of medical therapy)

Untreated eating disorder, active substance misuse, untreated major psychiatric illness
Inability to comply with lifelong follow-up and supplementation
Prohibitive operative risk

MDT: surgeon, dietitian, psychologist, physician/endocrinologist
*Screen and treat H. pylori** (especially before RYGB - the excluded stomach becomes inaccessible to endoscopy*)
Gastroscopy - hiatus hernia, Barrett's (*severe GORD or Barrett's -> RYGB, NOT sleeve*)
OSA screen, HbA1c, lipids, TFTs, liver screen/fibrosis staging
Baseline nutrition: iron studies, B12, folate, vitamin D, calcium, PTH, zinc, thiamine, vitamin A
Very-low-energy diet for 2-4 weeks pre-op - shrinks the liver, improves access
Contraception and defer pregnancy for 12-18 months

Lifelong follow-up and supplementation - the physician's job

Daily multivitamin (often 2 tablets), calcium 1200-1500 mg + vitamin D, iron, B12
Monitoring: 3, 6, 12 months, then ANNUALLY FOR LIFE
- FBE, iron studies, B12, folate, vitamin D, calcium, PTH, magnesium, zinc, copper, vitamin A, albumin, LFTs
*Loss to follow-up is the commonest cause of severe deficiency*

Deficiency	Highest risk	Consequence
Iron	RYGB, BPD >> sleeve	Microcytic anaemia; acid reduction + duodenal bypass
Calcium + vitamin D	RYGB, BPD	Secondary hyperparathyroidism -> osteoporosis, fracture
B12	All (dec intrinsic factor + acid)	Macrocytic anaemia, subacute combined degeneration
THIAMINE	Any, especially with persistent vomiting	*Wernicke encephalopathy - can occur within WEEKS; give IV thiamine BEFORE glucose*
Vitamins A, E, K	BPD/duodenal switch	Night blindness, coagulopathy
Copper, zinc, selenium	RYGB, BPD	Myeloneuropathy, cytopenias, cardiomyopathy
Protein-energy malnutrition	BPD	Oedema, hypoalbuminaemia

Early: anastomotic/staple-line leak (tachycardia is the earliest sign - do not wait for peritonism), bleeding, VTE
Late
- Internal hernia and small bowel obstruction after RYGB - *intermittent post-prandial pain; CT is frequently NORMAL; a low threshold for laparoscopy*
- Marginal ulcer at the gastrojejunal anastomosis - smoking, NSAIDs, H. pylori; lifelong PPI in high risk
- Stricture, band slippage/erosion, gastro-gastric fistula
- Gallstones in ~30% with rapid weight loss - consider prophylactic ursodeoxycholic acid for 6 months
- GORD and de novo Barrett's after SLEEVE - the main reason sleeve is avoided in reflux disease

Dumping syndrome
- Early (10-30 min): osmotic - cramps, diarrhoea, flushing, tachycardia
- Late (1-3 h): reactive hypoglycaemia from a GLP-1-driven insulin surge
- Management: small, low-simple-carbohydrate meals, separate fluids from solids, acarbose, octreotide
Post-bariatric hypoglycaemia - months to years after RYGB; confirm with a mixed-meal test, NOT an OGTT
Altered pharmacokinetics - *avoid NSAIDs and slow-release/enteric-coated formulations; monitor levels of narrow-therapeutic-index drugs; oral contraceptive efficacy may fall after malabsorptive surgery*
Nephrolithiasis (calcium oxalate) after malabsorptive surgery - enteric hyperoxaluria
Alcohol - faster absorption, higher peak; new-onset alcohol use disorder after RYGB
Psychological - body image, excess skin, increased self-harm and suicide risk post-operatively

T2DM, hypertension, dyslipidaemia, OSA, MASLD/MASH, PCOS, infertility, osteoarthritis, GORD
Depression, binge eating disorder, prior trauma - screen pre-operatively
Pregnancy - defer 12-18 months; reduced gestational diabetes and macrosomia, but increased small-for-gestational-age; use a mixed-meal or HbA1c rather than OGTT (dumping)
Idiopathic intracranial hypertension - improves markedly
Cancer risk - reduced overall, notably endometrial and breast
GLP-1 receptor agonists and tirzepatide - increasingly used before, instead of, or after surgery

Mortality reduced ~30-40% at 10 years vs matched non-surgical obesity (SOS study); cardiovascular and cancer deaths both fall
Diabetes remission is greatest with RYGB and greatest with shorter diabetes duration and preserved beta cell function - relapse in a third by 5-10 years, but with better long-term control than medical therapy
Weight regain in 20-30% by 10 years -> revision surgery or adjunctive GLP-1 therapy
Band removal/revision rates historically 40-50% at 10 years - the reason it fell out of favour
Nutritional complications accumulate over decades, not months - *annual monitoring for life is the single most important long-term instruction*

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