Gastric outlet obstruction
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- What are the common causes of gastric outlet obstruction in adults?
The 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?
The 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?
The classical abnormality is:
Hypochloraemic
Hypokalaemic
Metabolic alkalosis
Often associated with hyponatraemia and volume depletion.- Why does vomiting lead to metabolic alkalosis?
Gastric 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?
Hypokalaemia 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?
Possible 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?
Investigations 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?
Initial 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).
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