Define Gastric Outlet Obstruction. Describe its clinical features and management.

The Concept

Gastric outlet obstruction is a mechanical blockage to the emptying of the stomach at or near the pylorus, so that ingested food cannot pass into the duodenum. The two important causes reflect a historical shift: traditionally it was a benign complication of chronic peptic ulceration (fibrosis and scarring narrowing the pylorus — 'cicatricial pyloric stenosis'), but with modern ulcer treatment the leading cause is now malignancy — a distal gastric carcinoma or a carcinoma of the head of the pancreas.

Clinical Features

The stomach fills but cannot empty, so the patient has projectile vomiting of large volumes of undigested, non-bile-stained food (the obstruction is proximal to the bile duct), often hours after eating. There is early satiety, weight loss and dehydration, a visible gastric peristalsis in a thin patient, and a succussion splash (a splashing sound on shaking the abdomen, from retained fluid and food).

The Classic Metabolic Picture

Persistent vomiting of acidic gastric juice loses hydrogen and chloride ions (and, secondarily, potassium), producing the characteristic hypochloraemic, hypokalaemic metabolic alkalosis with paradoxical aciduria — a favourite exam finding that must be corrected before any intervention.

Management

Management begins with resuscitation and correction of the fluid and electrolyte abnormality (isotonic saline with potassium), nasogastric decompression of the stomach, and nutritional support. The cause is then treated: benign strictures by endoscopic balloon dilatation or surgery, and malignant obstruction by resection, stenting or a bypass (gastrojejunostomy) as appropriate.

Benign VS Malignant — the Key Distinction

Distinguishing the cause matters greatly. A benign peptic stricture tends to occur in a patient with a long ulcer history, whereas malignant obstruction is suggested by a short history of weight loss, anorexia and anaemia in an older patient. Endoscopy with biopsy makes the distinction and is essential, because the treatment and prognosis differ entirely.

A Note on Resuscitation

The metabolic derangement is not a footnote but a priority: the hypochloraemic, hypokalaemic metabolic alkalosis and dehydration must be corrected with saline and potassium before any endoscopy, dilatation or surgery, because operating on a dehydrated, alkalotic, hypokalaemic patient is dangerous. Nasogastric decompression relieves the distended stomach meanwhile.

The Bottom Line

Gastric outlet obstruction gives projectile non-bilious vomiting of undigested food with a hypochloraemic hypokalaemic metabolic alkalosis; it is now most often malignant, so correct the electrolytes, decompress, and biopsy at endoscopy before treating the cause.

A Note on the Paediatric Mimic

It is worth distinguishing this acquired adult condition from infantile hypertrophic pyloric stenosis, a congenital cause of gastric outlet obstruction in babies (typically 3–6 weeks old) from hypertrophy of the pyloric muscle — presenting with projectile non-bilious vomiting, a palpable 'olive' and visible peristalsis, and the same hypochloraemic hypokalaemic metabolic alkalosis, but treated by Ramstedt's pyloromyotomy. Recognising the shared physiology (loss of gastric acid) while separating the very different causes and treatments is a common exam theme.

The metabolic picture is characteristic — correct before surgery.

• Gastric outlet obstruction = mechanical block to gastric emptying at the pylorus.
• Causes: chronic peptic ulcer scarring (benign) and distal gastric/pancreatic carcinoma (now the leading cause).
• Projectile non-bilious vomiting of undigested food, visible peristalsis, succussion splash, weight loss, dehydration.
• Classic hypochloraemic hypokalaemic metabolic alkalosis (loss of gastric HCl).
• Correct fluids/electrolytes + NG decompression first, then treat the cause (dilatation/surgery, or manage the cancer).