Gastric outlet obstruction

Synopsis

Recognise mechanical failure of gastric emptying, correct volume and chloride depletion, decompress safely, identify benign or malignant narrowing and select durable endoscopic or surgical relief.

Gastric outlet obstruction causes early satiety, postprandial fullness and large-volume non-bilious vomiting of stale food because the block lies before bile enters the duodenum.
Repeated hydrogen and chloride loss produces hypochloraemic metabolic alkalosis; volume contraction activates aldosterone and promotes renal potassium and hydrogen loss.
Initial management is nil by mouth, nasogastric decompression, aspiration protection and measured chloride, potassium and volume correction before sedation or definitive intervention.

Key red flags

Progressive vomiting, weight loss, iron-deficiency anaemia or a palpable epigastric mass requires urgent investigation for gastric, pancreatic or duodenal malignancy.

Fever, guarding, lactate rise, haematemesis or respiratory deterioration suggests aspiration, perforation, ischaemia or bleeding rather than uncomplicated retention.

Malignant trajectory

Progressive early satiety, weight loss, anaemia or a mass suggests infiltrative or extrinsic cancer until excluded.

Aspiration complication

Cough, hypoxaemia, fever or new infiltrates after vomiting indicates respiratory contamination and may require airway support.

Investigation priorities

Renal profile, magnesium and blood gasFirst step

Quantify dehydration, alkalosis and potassium or chloride depletion.

Management branches

Malignant obstructionRestore physiology before choosing durability

A 74-year-old has three weeks of stale-food vomiting, 7 kg weight loss, chloride 78 mmol/L, potassium 2.8 mmol/L and CT thickening at the gastric antrum. He weighs 65 kg, has pH 7.51 and bicarbonate 35 mmol/L, creatinine 90 micromol/L, adequate urine output and no heart failure or potassium-raising medicines.

Keep nil by mouth and decompress 2.3 litres of retained gastric fluid. After senior volume assessment and ECG, prescribe a ready-mixed one-litre bag of sodium chloride 0.9% with potassium chloride 40 mmol by controlled peripheral IV infusion over eight hours: 125 mL/hour and 5 mmol potassium/hour. This individually chosen first replacement is within NHS SPS adult NBM guidance of 20–40 mmol/L, peripheral concentration no greater than 40 mmol/L and usual rate no greater than 10 mmol/hour. Record intake, gastric losses, urine output, pressure, pulse, lungs and the infusion site; check potassium, sodium, chloride, magnesium and creatinine after the first bag before prescribing further replacement.
After the first infusion potassium is 3.2 mmol/L without creatinine rise or pulmonary congestion; magnesium is normal. Further chloride/potassium replacement is adjusted to ongoing losses and repeat results. By the next day, potassium is 3.6, chloride 96, pH 7.43 and pulse 86/min, with adequate urine output and effective decompression. Endoscopy can now proceed with a documented sedation/aspiration plan: the non-traversable antral mass is sampled with at least eight targeted biopsies, confirming gastric adenocarcinoma.

Key medicines

Omeprazole for a benign peptic-ulcer componentOnce decompression has restored a reliable oral route, give omeprazole 20 mg orally once daily for a gastric-ulcer component; the current SmPC expects healing within 4 weeks and permits a further 4 weeks when healing is incomplete. A poorly responsive ulcer may use 40 mg once daily under specialist review while persistent obstruction and malignancy are reinvestigated. Use the morning dose as an intact capsule with water once oral absorption is reliable; do not chew or crush the enteric-coated contents.Do not rely on PPI response to label an adult outlet obstruction benign. Exclude and biopsy gastric cancer and correct electrolyte and volume deficits before procedures. In hepatic impairment the SmPC states 10–20 mg daily may be sufficient, so avoid automatic escalation to 40 mg. Review the nelfinavir contraindication, clopidogrel and CYP2C19 interactions, acute interstitial nephritis and prolonged-treatment magnesium or B12 risk. No dose adjustment is required solely for renal impairment.

Premixed potassium chloride 0.3% in sodium chloride 0.9% for vomiting-related depletionFor the monitored 65 kg adult in the worked case, the initial prescription is one litre containing 40 mmol potassium over eight hours by controlled peripheral IV infusion. NHS SPS supports 20–40 mmol/L initially when a moderately hypokalaemic adult cannot use the enteral route; do not exceed 40 mmol/L peripherally or the usual 10 mmol/hour rate. Choose every subsequent dose from repeat potassium and continuing losses, not a prewritten series of bags. Never inject concentrated potassium directly; use a commercially prepared diluted bag.Before and during infusion assess urine flow, fluid balance, potassium, sodium, chloride, magnesium, renal function and acid-base status; obtain ECG monitoring according to clinical risk, concentration and rate. The selected Baxter product is contraindicated in hyperkalaemia, hyperchloraemia, hypernatraemia, severe renal insufficiency with oliguria/anuria, uncompensated heart failure, Addison disease or product hypersensitivity. Lesser renal impairment requires lower individually reassessed doses. Review potassium-sparing diuretics, ACE inhibitors, ARBs and other potassium-raising medicines. Stop or reduce infusion for rising potassium or fluid overload and escalate new arrhythmia. Its total potassium ceiling is 2–3 mmol/kg/24 hours, not a replacement target.

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