Suspected bowel obstruction

Bowel obstruction is failure of intestinal contents to pass because of a mechanical block or a loss of propulsion. It presents with colicky abdominal pain, vomiting, distension and absolute constipation, in a mix that depends on the level. The decisions are whether the bowel is viable, whether the patient needs theatre, and what the cause is.

Classification.

• Level: small bowel (high or low) or large bowel.
• Mechanism: mechanical (luminal, mural or extramural) or functional (paralytic ileus, pseudo-obstruction).
• Degree: partial or complete.
• Vascular compromise: simple obstruction, strangulation (blood supply compromised), and closed loop (both ends obstructed, for example volvulus or large bowel obstruction with a competent ileocaecal valve), which can perforate quickly.

Pathophysiology. Gas and fluid accumulate proximal to the block, causing distension and raised intraluminal pressure, then mural oedema, venous congestion and arterial ischaemia. Vomiting and third space loss produce hypovolaemia, hypokalaemia and hypochloraemic metabolic alkalosis. Bacterial translocation causes sepsis. A caecal diameter over 12 cm carries a high risk of perforation.

Patterns by level.

• High small bowel: early repeated vomiting (bilious), little distension, may still pass stool.
• Low small bowel: colicky central pain, distension, late faeculent vomiting, constipation.
• Large bowel: gradual distension, pain, constipation or obstipation, late vomiting.

Key distinctions. Pain that changes from colicky to constant, with fever, tachycardia, localised tenderness or rising lactate, signals strangulation. Passage of stool or flatus in the first hours does not exclude obstruction. Postoperative ileus and pseudo-obstruction mimic mechanical obstruction and are treated differently.

History.

• Pain (colicky, intermittent, then constant), vomiting (bilious or faeculent), time of last stool and flatus, distension.
• Previous abdominal or pelvic surgery (adhesions are the leading cause of small bowel obstruction in adults), hernias, radiotherapy, malignancy, inflammatory bowel disease, diverticular disease, gallstones, previous volvulus, constipation.
• Change in bowel habit, rectal bleeding, weight loss (colorectal cancer).
• Drugs: opioids, anticholinergics, clozapine, calcium channel blockers, vincristine, iron and calcium supplements, laxative misuse.
• Region specific points: sigmoid volvulus is common in parts of Africa, Asia and Eastern Europe, Ascaris worm bolus obstruction in children, abdominal tuberculosis strictures, and hernias presenting late.

Examination.

• Hydration, pulse, blood pressure, temperature, respiratory rate, urine output, mental state.
• Abdomen: distension, visible peristalsis, scars, tenderness, localised guarding, peritonism, masses, bowel sounds (high pitched and tinkling early, absent late).
• All hernial orifices (inguinal, femoral, umbilical, incisional, obturator is palpable on rectal or vaginal examination), a tender irreducible hernia, and testes.
• Rectal examination: empty rectum, mass, impaction, blood.

Red flags.

• Constant pain, localised tenderness, peritonism, fever, tachycardia, hypotension, lactate over 2 mmol/L.
• Blood in the stool, irreducible tender hernia, rapidly increasing distension, caecum over 9 cm on radiograph (over 12 cm is very high risk).
• Closed loop signs on CT, free fluid, pneumatosis or portal venous gas.

Special groups. Neonates and infants (bilious vomiting needs same day paediatric surgical assessment), children (intussusception, with redcurrent jelly stool, vomiting and drawing up of legs), pregnancy (volvulus, adhesions; MRI preferred, and surgery is not delayed), older adults (cancer, impaction, pseudo-obstruction), and patients with known malignancy or peritoneal disease.

Small bowel.

• Adhesions and bands, strangulated or incarcerated hernia (inguinal, femoral, umbilical, incisional, obturator, internal), post-bariatric internal hernia.
• Malignancy (primary small bowel tumour, peritoneal carcinomatosis, metastasis), Crohn stricture, tuberculous stricture, radiation enteritis, ischaemic stricture.
• Gallstone ileus, bezoar, foreign body, Ascaris bolus, intussusception, small bowel volvulus, malrotation with midgut volvulus, Meckel diverticulum with band, intramural haematoma.

Large bowel.

• Colorectal cancer, sigmoid volvulus, caecal volvulus, diverticular stricture, faecal impaction, ischaemic stricture, Crohn stricture.
• Extrinsic compression (ovarian cancer, pelvic mass, endometriosis), hernia (sliding, Richter), intussusception with a lead point, Hirschsprung disease (children), anorectal malformation.

Functional.

• Paralytic ileus: postoperative, sepsis, peritonitis, acute pancreatitis, retroperitoneal haemorrhage, spinal injury, electrolyte disturbance (hypokalaemia, hypomagnesaemia, hypercalcaemia, hyponatraemia), hypothyroidism, drugs (opioids, anticholinergics).
• Acute colonic pseudo-obstruction (Ogilvie syndrome), toxic megacolon, mesenteric ischaemia.

Mimics. Gastric outlet obstruction, severe constipation, gastroenteritis, acute pancreatitis, diabetic ketoacidosis, acute urinary retention, pregnancy related vomiting, and perforation without obstruction.

Step 1. Resuscitate and look for peritonism or strangulation, which move the patient to theatre.

Step 2. First line tests: full blood count, urea, creatinine, electrolytes (low potassium, low chloride), bicarbonate, venous gas with lactate (rising lactate indicates ischaemia but normal lactate does not exclude it), CRP, glucose, calcium, magnesium, liver tests, lipase, group and crossmatch, pregnancy test, and ECG.

Step 3. Imaging.

• Abdominal radiograph: small bowel over 3 cm in diameter, large bowel over 6 cm, caecum over 9 cm. A sigmoid volvulus shows a coffee bean loop with its apex pointing to the right upper quadrant. Air-fluid levels at different heights suggest obstruction but are not specific. Plain films miss early obstruction and closed loops.
• CT abdomen and pelvis with intravenous contrast has a sensitivity and specificity of about 90 to 95% for obstruction, shows the transition point and cause (adhesion, hernia, tumour, volvulus), and finds strangulation (reduced wall enhancement, wall thickening, mesenteric oedema, free fluid, pneumatosis, portal venous gas, closed loop, whirl sign).
• Water soluble contrast study for adhesive small bowel obstruction: 100 mL given by mouth or nasogastric tube, with an abdominal film at 8 to 24 hours. Contrast reaching the colon within 24 hours predicts non-operative resolution, and failure to reach it by 24 hours predicts the need for surgery. It also reduces time in hospital.
• Ultrasound for hernias and intussusception. Contrast enema or CT for large bowel level and cause.

Step 4. Targeted tests: rigid or flexible sigmoidoscopy for volvulus and distal tumour, colonoscopy after decompression, tumour markers and staging CT for cancer, and stool and parasite tests where Ascaris is possible.

Limitations. CT may not distinguish ileus from partial obstruction without a clear transition point. Contrast needs care in kidney impairment. Radiographic dimensions do not by themselves predict strangulation.

Supportive care ("drip and suck").

• Nil by mouth, nasogastric tube on free drainage (aspirate every 4 hours), urinary catheter, and monitoring.
• Isotonic crystalloid: 1 L over 1 to 2 hours (500 mL boluses if hypotensive), then maintenance of 1.5 to 2 mL/kg/hour plus replacement of nasogastric losses millilitre for millilitre.
• Potassium replacement to a level of 4.0 mmol/L or more: maximum 10 mmol/hour through a peripheral line and 20 mmol/hour through a central line with ECG monitoring; reduce the rate in kidney impairment. Replace magnesium to over 0.7 mmol/L (magnesium sulphate 2 g IV over 20 minutes; monitor reflexes and respiratory rate; reduce in kidney impairment).
• Analgesia: paracetamol 1 g IV every 6 hours (maximum 4 g daily; 3 g daily if weight under 50 kg, malnutrition, alcohol excess or liver disease), and morphine 0.05 to 0.1 mg/kg IV in 2 mg boluses every 5 minutes (maximum 10 mg before reassessment; monitor respiration and sedation; use fentanyl in kidney impairment). Avoid NSAIDs.
• Antiemetic: ondansetron 4 mg IV every 8 hours (maximum 16 mg daily). Avoid metoclopramide and other prokinetics in complete mechanical obstruction.
• Thromboprophylaxis: enoxaparin 40 mg subcutaneously once daily (20 mg daily if CrCl 15 to 30 mL/min; unfractionated heparin 5000 units subcutaneously every 8 to 12 hours if CrCl under 15 mL/min).
• Antibiotics only when strangulation, perforation or sepsis is suspected, and as perioperative cover: ceftriaxone 2 g IV once daily (maximum 4 g daily) plus metronidazole 500 mg IV every 8 hours (maximum 1.5 g daily); monitor creatinine, liver tests and diarrhoea.

Small bowel obstruction.

• Immediate surgery for peritonitis, strangulation, closed loop obstruction, irreducible tender hernia, or clinical deterioration. Do not wait for contrast studies.
• Adhesive small bowel obstruction without these features: non-operative management for up to 72 hours with serial examination every 4 to 6 hours, water soluble contrast at 6 to 24 hours, and surgery if there is no resolution (contrast not reaching the colon by 24 hours, persistent high nasogastric output, or no passage of stool or flatus by 48 to 72 hours). About 70 to 80% of partial adhesive obstructions settle.
• Laparoscopic or open adhesiolysis, bowel resection when non-viable, hernia repair, and enterolithotomy for gallstone ileus.
• Ascaris bolus: nil by mouth and nasogastric drainage, then albendazole 400 mg orally as a single dose once the obstruction has settled (avoid in the first trimester of pregnancy; monitor liver tests with repeated use), with surgery for non-resolution.
• Intussusception in children: air or saline enema reduction under radiological direction, with surgery for failure or peritonitis.

Large bowel obstruction.

• Complete obstruction with a competent ileocaecal valve is a closed loop. Surgery is usually needed urgently, particularly with caecal diameter over 12 cm, peritonism or ischaemia.
• Malignant obstruction: self expanding metal stent as a bridge to surgery or for palliation in selected patients (avoid in curative right sided disease and with perforation), or resection with primary anastomosis, Hartmann procedure or defunctioning stoma.
• Sigmoid volvulus: rigid or flexible sigmoidoscopic decompression with a flatus tube left in situ for 24 hours, successful in about 85%. Because recurrence is high (up to about 60 to 70%), arrange elective sigmoid colectomy in the same admission when the patient is fit. Emergency surgery for gangrene, perforation or failed decompression.
• Caecal volvulus: surgery (right hemicolectomy).
• Faecal impaction: manual disimpaction, enemas, then laxatives.

Ileus and pseudo-obstruction.

• Treat the cause, stop opioids and anticholinergics where possible, correct potassium to 4.0 mmol/L or more and magnesium to over 0.7 mmol/L, keep nil by mouth with nasogastric drainage for vomiting, mobilise early and avoid fluid overload.
• Acute colonic pseudo-obstruction with caecal diameter over 12 cm, or no improvement after 24 to 48 hours of supportive care, and no mechanical obstruction on contrast imaging: neostigmine 2 mg IV over 3 to 5 minutes; maximum 2 mg in a single dose (repeat once if no response, after specialist review); continuous ECG and blood pressure for at least 30 minutes with atropine 0.6 to 1.2 mg IV ready for symptomatic bradycardia; avoid with mechanical obstruction, bradycardia under 60 beats/min, bronchospasm, recent myocardial infarction, active ischaemia, pregnancy and active bleeding; reduce to 1 mg in kidney impairment. Colonoscopic decompression, or caecostomy when it fails.

Malignant bowel obstruction not suitable for surgery.

• Dexamethasone 8 mg subcutaneously or IV once daily for 3 to 5 days, then stop if there is no benefit; monitor glucose and use gastric protection.
• Octreotide 100 micrograms subcutaneously every 8 hours, titrated to a maximum of 600 micrograms daily; monitor glucose and gallstone symptoms.
• Hyoscine butylbromide 20 mg subcutaneously every 6 hours (or 60 to 120 mg by 24 hour subcutaneous infusion); maximum 120 mg daily; monitor for dry mouth, urinary retention and tachycardia; avoid with prokinetics.
• Opioid analgesia, antiemetics and a venting gastrostomy where appropriate, with palliative care input.

Monitoring. Hourly observations in the first 6 hours, then every 4 hours, hourly urine output, nasogastric volumes, daily electrolytes and creatinine, lactate when changing, serial abdominal examination, and repeat imaging for deterioration.

Referral and escalation. General surgery for all patients on first recognition. Paediatric surgery for children. Critical care for shock or sepsis. Gastroenterology or interventional radiology for stenting and decompression. Oncology and palliative care for malignant obstruction. Nutrition support if more than 5 to 7 days without adequate intake.

Admission criteria. All patients with suspected obstruction are admitted. A patient with chronic constipation and a soft abdomen, no vomiting and a normal radiograph can be treated as an outpatient.

Discharge and safety netting. Discharge when eating and passing stool, with a plan for the cause (elective hernia repair, sigmoid colectomy, oncology follow up). Patients are told to return for vomiting, colicky pain, distension, no stool or flatus, fever, severe constant pain or a painful hernia.