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What are the common causes of gastric outlet obstruction in adults? SpoilerThe causes can be divided into benign and malignant. Benign Peptic ulcer disease causing pyloric stenosis Chronic pancreatitis Caustic ingestion Post-surgical strictures Crohn’s disease Malignant Distal gastric cancer (most common modern cause) Pancreatic head cancer Duodenal carcinoma Periampullary tumours Historically peptic ulcer disease was the commonest cause, but malignancy is now more common. Why does gastric outlet obstruction cause vomiting of undigested food? SpoilerThe obstruction occurs at the pylorus or proximal duodenum, preventing gastric emptying. Food therefore remains in the stomach for prolonged periods and is vomited before reaching the small intestine, so it appears undigested. What electrolyte and acid–base abnormalities are classically seen? SpoilerThe classical abnormality is: Hypochloraemic Hypokalaemic Metabolic alkalosis Often associated with hyponatraemia and volume depletion. Why does vomiting lead to metabolic alkalosis? SpoilerGastric secretions contain hydrochloric acid (HCl). Vomiting causes loss of: Hydrogen ions Chloride ions Loss of hydrogen ions leads to metabolic alkalosis, and loss of chloride contributes to hypochloraemia, which also impairs renal bicarbonate excretion and worsens the alkalosis. Why does hypokalaemia occur in gastric outlet obstruction? SpoilerHypokalaemia occurs due to: Renal potassium loss from activation of the renin–angiotensin–aldosterone system due to dehydration. Hydrogen–potassium exchange in the kidney during metabolic alkalosis, where potassium is excreted to retain hydrogen ions. What clinical signs might you find on examination? SpoilerPossible signs include: Epigastric distension Succussion splash (if stomach contains retained fluid) Visible gastric peristalsis Signs of dehydration (tachycardia, hypotension) Possible weight loss if chronic What investigations would you perform to confirm the diagnosis? SpoilerInvestigations include: Blood tests: FBC, U&E, LFTs, ABG Nasogastric aspiration (large residual volume) Upper GI endoscopy (OGD) – confirms obstruction and allows biopsy CT abdomen – helps identify malignancy or extrinsic compression OGD is the key diagnostic test. How would you manage this patient initially? SpoilerInitial management is resuscitation and decompression: Nil by mouth Nasogastric tube for gastric decompression IV fluids to correct dehydration Correct electrolyte abnormalities IV proton pump inhibitor Arrange urgent endoscopy Definitive treatment depends on the cause (e.g., endoscopic dilation, surgery, or oncological treatment).