Bowel obstruction (ileus) is a halt in the onward passage of bowel contents. Mechanical obstruction is due to a physical obstacle — most often adhesions or a hernia in the small bowel, and cancer in the large bowel — whereas paralytic ileus is a temporary loss of motility. Initial treatment is decompression with a nasogastric tube and fluids; urgent surgery is needed for strangulation, complete obstruction that does not resolve, or an incarcerated hernia.
What is bowel obstruction?
Bowel obstruction (ileus) is a halt in the normal onward passage of bowel contents. It has two main forms. In mechanical obstruction there is a real obstacle blocking the bowel lumen; depending on the site, we speak of small or large bowel obstruction. In paralytic (adynamic) ileus there is no mechanical obstacle, but the bowel temporarily stops contracting.
Two dangerous situations deserve special attention: the closed loop (obstruction at two points) and strangulation, in which the blood supply to the bowel wall is cut off and necrosis is threatened. Both are surgical emergencies.
How common is it?
Small bowel obstruction is one of the commonest reasons for emergency surgical admission with an "acute abdomen". Most cases are due to adhesions from previous abdominal surgery or to hernias.
In the large bowel, obstruction is less common but is often linked to more serious underlying causes — chiefly cancer. Early identification of the cause determines both the treatment and the prognosis.
How does it present?
The classic symptoms of mechanical obstruction are:
- Colicky abdominal pain — pain that comes in waves.
- Abdominal distension — more marked in low obstructions and in the large bowel.
- Vomiting — early in high small bowel obstructions, late and potentially feculent in low ones.
- Failure to pass gas and stool — absolute constipation.
In paralytic ileus the abdomen is distended but pain is usually less intense, with reduced or absent bowel sounds.
How is it diagnosed?
Diagnosis rests on combining the clinical picture with imaging, aiming to define the site, the cause and any signs of ischaemia:
- Clinical assessment — a distended, tender abdomen; high-pitched or tinkling bowel sounds in mechanical obstruction, silence in paralytic ileus or the late phase. Hernial orifices are always checked.
- Plain abdominal X-ray — dilated bowel loops and air-fluid levels.
- CT of the abdomen and pelvis with contrast — the investigation of choice: it localises the obstruction, reveals the cause, and shows signs of strangulation or ischaemia.
- Laboratory tests — electrolytes, inflammatory markers and lactate, which help gauge severity.
In selected partial small bowel obstructions, water-soluble contrast (gastrografin) has a dual, diagnostic and therapeutic role.
What are the causes?
Identifying the cause determines both treatment and prevention of recurrence:
- Adhesions — scar bands after previous abdominal surgery; the commonest cause of small bowel obstruction.
- Hernias — inguinal, femoral or incisional, when a loop of bowel becomes incarcerated and strangulated.
- Malignancy — the commonest cause of large bowel obstruction.
- Volvulus — mainly of the sigmoid or the caecum.
- Inflammatory strictures — diverticulitis, Crohn's disease; more rarely intussusception or a foreign body.
- Paralytic ileus — after surgery, with peritonitis, electrolyte disturbances, or certain medications (e.g. opioids).
Modern treatment options
Management is individualised according to the cause, the site and the severity. Many partial obstructions resolve conservatively, while strangulation and complete obstruction require urgent surgery.
For details of the techniques, see the Surgical Services page and the Inguinal hernia and Colon cancer pages.
Conservative Decompression
The first step in a stable patient: nil by mouth, a nasogastric tube for decompression, intravenous fluids and electrolyte correction, with close monitoring. Many adhesive small bowel obstructions resolve this way.
Surgical Correction
When there is strangulation, a closed loop or obstruction that does not resolve, surgery is urgent. Depending on the finding: adhesiolysis, resection of a non-viable segment with anastomosis or a stoma — laparoscopically or open.
Treating the Cause
The definitive solution addresses the underlying cause: hernia repair, removal of an obstructing tumour or — in selected cases of obstructing colon cancer — endoscopic stent placement as a "bridge" to surgery.
Frequently asked questions
When is bowel obstruction an emergency?
Bowel obstruction always requires prompt medical assessment. It becomes a surgical emergency when there are signs of strangulation or bowel ischaemia: constant, severe pain (rather than cramping in waves), fever, tachycardia, and a rigid, tender abdomen. In these cases urgent surgery is needed to prevent necrosis and perforation.
What is the commonest cause?
In the small bowel, the commonest cause is adhesions — scar bands that form after previous abdominal surgery — followed by hernias. In the large bowel, the commonest cause is cancer that progressively narrows the lumen, along with volvulus and inflammatory strictures.
Is surgery always needed?
No. A large proportion of partial small bowel obstructions, especially adhesive ones, resolve with conservative treatment: nil by mouth, a nasogastric tube for decompression, intravenous fluids and correction of electrolytes, with close monitoring. Surgery is required when there is strangulation, complete obstruction that does not resolve, an incarcerated hernia, or an obstructing tumour.
What is paralytic ileus?
Paralytic (or adynamic) ileus is a halt in propulsion without a mechanical obstacle: the bowel temporarily stops contracting. It is common after abdominal surgery, and also occurs with peritonitis, electrolyte disturbances or certain medications (e.g. opioids). It is managed conservatively by correcting the underlying cause.
Can bowel obstruction recur?
Yes, adhesive obstruction in particular can recur, as adhesions persist or re-form. Treating the underlying cause — hernia repair, tumour removal — reduces the risk of a further episode. Individualised follow-up helps with early recognition and treatment.