Large bowel obstruction

What is large bowel obstruction?

Large bowel obstruction is a blockage of the colon or rectum that stops stool and gas from passing. Gas and stool build up above the blockage and the colon stretches. It can develop slowly, as with a tumour, or suddenly, as with a twist, and it needs hospital assessment because the bowel can tear or lose its blood supply.

The large bowel, or colon, absorbs water and stores stool before it leaves through the rectum and anus. Because a stretched colon can tear and a twisted one can lose its blood supply, large bowel obstruction needs prompt assessment in hospital.

What causes large bowel obstruction?

In adults, bowel cancer is the most common cause of large bowel obstruction. Other causes are volvulus, where a loop of colon twists, narrowing after repeated diverticulitis or from inflammatory bowel disease, and a hard mass of stool. Pseudo-obstruction mimics a blockage when the bowel stops working without anything physically blocking it.

• Bowel cancer narrowing or blocking the colon or rectum
• Volvulus, where a loop of colon twists on itself
• Narrowing (stricture) after repeated diverticulitis
• Narrowing from inflammatory bowel disease
• Severe constipation with a hard mass of stool
• Pseudo-obstruction, where the bowel stops working without a physical blockage

What are the symptoms?

Large bowel obstruction usually causes a swollen abdomen, crampy pain, constipation and being unable to pass wind. Nausea and vomiting can follow. When a tumour is the cause, a change in bowel habit, blood in the stool or weight loss may have come first.

• Swelling and bloating of the abdomen
• Crampy abdominal pain
• Constipation and being unable to pass wind
• Nausea, with vomiting later in the illness
• A change in bowel habit or blood in the stool in the weeks before, when a tumour is the cause

When is a blocked bowel an emergency?

A swollen abdomen with no wind or stool passing needs same-day hospital assessment. Go to an emergency department for severe or constant pain, fever, a fast heart rate, feeling faint or vomiting that will not stop. Earlier warning signs such as blood in the stool or a lasting change in bowel habit also need prompt review.

The warning signs below need prompt attention.

• Severe or constant abdominal pain
• A tight, very swollen abdomen with no wind or stool passing
• Fever, a fast heart rate or feeling faint
• Vomiting that will not stop
• Black or bloody stools, or unexplained weight loss beforehand

How is it diagnosed?

Large bowel obstruction is diagnosed from your history, an examination and blood tests, with an X-ray and a CT scan. CT is the usual test to show where the blockage is, what is causing it and whether the bowel is at risk. A tube or scope may be passed into the lower bowel in selected cases.

• Questions about bowel habit, weight loss, bleeding and past operations
• Examination of the abdomen and a gentle rectal examination
• Blood tests for hydration, salts, blood count and infection
• Abdominal X-ray
• CT scan, the usual test to show where the blockage is and what is causing it
• Examination of the lower bowel with a tube or scope in selected cases

How is large bowel obstruction treated?

Treatment depends on the cause. A volvulus of the lower colon may be untwisted with a tube passed through the rectum. A blockage from a left-sided bowel cancer may be opened with a stent in selected patients. Otherwise surgery removes the blocked section, joining the ends where safe or forming a stoma.

• Fluids through a drip and a stomach tube if vomiting
• A tube passed through the rectum to untwist a volvulus of the lower colon
• A self-expanding metal stent to open a blockage from a left-sided bowel cancer in selected patients
• Surgery to remove the blocked section, with the ends joined where safe
• A temporary or permanent stoma when joining the bowel is not safe
• Treatment of a stool mass or pseudo-obstruction without surgery where possible

What are the risks and complications?

An untreated large bowel obstruction can tear the stretched colon or cut off the blood supply to a twisted segment. Surgery carries risks such as leakage where the bowel is joined, wound infection, bleeding and later hernia. A stent has its own risks and is not suitable for everyone.

• A tear (perforation) of the stretched colon, with infection inside the abdomen
• Loss of blood supply to a twisted segment of bowel
• Dehydration and salt imbalance
• After surgery: leakage where the bowel is joined, wound infection, bleeding or a hernia at the wound
• For cancers that can be removed surgically, possible long-term disadvantages of a stent that are still being studied