Patient information from BMJ

Large bowel obstruction

Last published:Dec 10, 2024

A large bowel obstruction means that something is blocking your large bowel (lower digestive system). It is a medical emergency that usually needs surgery. 

Several things can cause a large bowel obstruction, including bowel cancer.

What is a large bowel obstruction?

The large bowel is the lower part of the digestive system. You might also hear it called the large intestine, lower intestine, or colon. Water and vitamins are absorbed into your body from your food from here. Waste material (stools) is then pushed down towards your rectum. 

When something blocks the large bowel and stops things passing through, it’s called a large bowel obstruction. This is a medical emergency, as the obstruction can cause serious problems. 

For example, you can become quickly dehydrated because you are not absorbing water. The bowel can become damaged (perforated), which can lead to an infection and damage to other parts of your body inside your abdomen. 

If you have a large bowel obstruction you will almost certainly need surgery.

Bowel cancer is one cause of large bowel obstruction. This happens when a tumour grows in the bowel. 

For more information on bowel cancer and its treatments, see our other patient information: Bowel cancer: what is it?; Bowel cancer: what are the treatment options?; and Bowel cancer: should I be screened?

Large bowel obstructions are more common in older people and people with cancer or who have had cancer in the past.

Other things that can cause large bowel obstructions include:

• Narrowing of part of the bowel. The medical name is 'stricture'. This can have several causes, including problems with blood vessels, and a condition called diverticular disease

• Twisting of the bowel. The medical name for this twisting is 'volvulus'

• Hernia (when part of your bowel moves into another part of the abdomen and becomes trapped)

• An object that has been swallowed, or an object inserted into the rectum

• Some cancers that only affect women, such as cervical cancer

• A condition that affects women called endometriosis. If you have endometriosis, tissue that should only grow inside the uterus (womb) grows on other parts of the body, including the bowel.

What are the symptoms of a large bowel obstruction?

Symptoms of a large bowel obstruction can include:

• Pain in the abdomen

• A hard, swollen abdomen

• Changes in your bowel habits: for example, you might need to go to the toilet more than usual, or you might not be able to go at all

• Stools can become either harder or softer than usual

• Unexplained weight loss

• Not being able to pass wind

• Feeling or being sick

• Bleeding from your rectum

• Fever. This is a sign of infection. It could mean that the bowel has become damaged (perforated) and that the contents of the bowel are leaking into the abdomen.

The symptoms are different depending on what has caused your obstruction. The cause can also affect whether the symptoms come on suddenly or more gradually over time. 

When bowel cancer is the cause, the symptoms come on gradually. Symptoms will probably include recent weight loss and bleeding from the rectum. This type of obstruction is more common in older people. 

When twisting (volvulus) is the cause, the symptoms come on quickly. This type of obstruction is more common in older people, and those:

• who have already had serious bowel problems;

• who have had abdominal surgery in the past;

• who have diabetes; and 

• who use laxatives (medicines to help you go to the toilet) for a long-term bowel condition.

When diverticular disease is the cause, the symptoms come on gradually. You will probably notice pain and tenderness in your abdomen. (For more information, see our leaflet: Diverticular disease.)

When narrowing of the bowel (stricture) is the cause, the symptoms will probably include having to go to the toilet a lot, and only producing a small amount of stool each time. 

This type of obstruction is more common in people who have had previous treatments such as surgery or radiotherapy in the abdomen. 

How is a large bowel obstruction diagnosed?

If you have symptoms of possible bowel obstruction, your doctor will want to examine you and arrange some tests. 

• During a physical exam, your doctor will listen to the sounds in your abdomen. They will also feel inside your rectum for anything unusual. This is called a digital rectal examination (DRE for short)

• If you are a woman you might also need a vaginal examination, especially if you have endometriosis

• A type of scan called a computed tomography (CT) scan can usually detect an obstruction and what has caused it

• You will probably have blood tests to look for anaemia (low iron levels that suggests bleeding somewhere inside your bowel) and to check your blood sugar levels and kidney function. Blood tests are also needed to check your blood type if you are going to have surgery

• Your stool can be tested to see if there is blood in it

• Other types of tests include a colonoscopy (where a long, thin tube with a tiny camera on the end is inserted into your rectum to look closely at the bowel). A test called a contrast enema can also be used in some situations to show a blockage.

What are the treatment options for a large bowel obstruction?

If you are told you have a large bowel obstruction you will not be allowed to eat or drink anything until your doctor knows more about what has caused the problem, and probably not until you have been treated. 

You probably won’t feel like eating anyway. And you can be given fluids through a very narrow tube that goes directly into your veins (an intravenous (IV) drip). You might also need to have:

• oxygen to breathe, to help make sure that you have enough oxygen in your blood;

• a blood transfusion - again, to increase the amount of oxygen in your blood;

• antibiotics;

• a tube called a catheter inserted into your bladder to drain urine and make sure that your body is making it normally;

• the contents of your stomach above the blockage removed. This is done using nasogastric decompression. A tube is inserted through your nose and the contents of your stomach are gently sucked out. This means you can have surgery more safely, and it should also make you feel more comfortable.

Everyone with a large bowel obstruction will need some kind of procedure or operation to clear the obstruction. But if your bowel is perforated (damaged or torn) you will probably need emergency surgery, because perforation can cause an infection. 

Different procedures are used to treat different types of blockage. For example, if you have an obstruction caused by bowel cancer, you will probably have surgery to remove the part of the bowel affected by the tumour.You may also have radiotherapy or chemotherapy (treatment with medicines).

If your obstruction is caused by a twisted bowel, you will probably need surgery to remove the part of the bowel that is twisted.

If you have a blockage caused by narrowing of the bowel, you might just need a procedure to gently open up the narrowed area.

People with other types of blockage, such as those caused by diverticular disease and endometriosis, often, but not always, need to have surgery to remove the obstruction. 

What happens next?

Having a large bowel obstruction usually means having major surgery. This can be life changing, at least for a while after the operation.

For example, some people need a colostomy after surgery. If you have a colostomy, the surgeon makes an opening in your abdomen and waste from your bowel is diverted to pass out through this opening into a bag, instead of passing out through the rest of your bowel and your rectum.

Not everyone who has surgery will need a colostomy. And many people only need it for a while until their bowel heals.

Many people recover well after surgery for a large bowel obstruction. But it is a major operation, and there are risks. For example, the bowel can perforate (tear), causing an infection. This can lead to sepsis. Your surgical team will discuss all the risks of surgery with you, as well as how these would be managed.

If you have bowel cancer your doctor will monitor you for at least 5 years after you finish treatment. You will occasionally need a test called a colonoscopy. A tiny camera on the end of a long, thin tube is inserted into the rectum so that your doctor can check for any problems.

If your large bowel obstruction was caused by something else, your doctor will explain what type of monitoring you will need and for how long.