Bowel Obstruction: Small Intestine and Large Intestine

A bowel obstruction happens when something blocks the normal passage of food, fluid or gas through the intestines. It is a condition that always needs prompt medical assessment, because a blockage in the small intestine or the large intestine can quickly lead to complications if it is not treated. This page explains what a bowel obstruction is, the symptoms to watch for, the common causes, and how a gastroenterologist works alongside your GP and, where needed, a surgeon to diagnose and manage the condition.

What Is a Bowel Obstruction?

The intestines form a long, muscular tube that moves digested food, fluid and gas from the stomach through to the back passage. When part of this tube becomes blocked, contents build up above the blockage. This causes swelling, pain and, depending on the site and severity of the blockage, nausea, vomiting or an inability to pass wind or a bowel motion. A bowel obstruction can affect the small intestine or the large intestine (the colon), and the two forms tend to behave a little differently.

Small Bowel Obstruction

The small intestine is the long section of bowel where most digestion and nutrient absorption takes place. A blockage here is called a small bowel obstruction. This is the more common of the two types, and in Australia, as in other developed countries, it is most often related to scar tissue (known as adhesions) that has formed after previous abdominal or pelvic surgery.

Large Bowel Obstruction

The large intestine absorbs water and forms stool before it is passed. A blockage in this part of the bowel is called a large bowel obstruction. It tends to develop more gradually than a small bowel obstruction and is most often linked to a growth or narrowing of the bowel wall.

Partial, Complete and Closed Loop Obstruction

Obstructions are also described by how severe they are. In a partial obstruction, some gas or stool can still pass through the narrowed section, while a complete obstruction stops everything from passing. A closed loop obstruction occurs when a single section of bowel becomes blocked at two points. Because this traps the segment and can quickly affect its blood supply, it is treated as a medical emergency.

What Is Bowel Pseudo-Obstruction?

Sometimes the bowel becomes swollen and behaves as though it is blocked, even though no physical blockage can be found on scans. This is called pseudo-obstruction, and it happens when the muscles of the bowel wall are not contracting properly. The symptoms can look very similar to a true mechanical obstruction, so it is important for your treating team to tell the two apart, as the management is different.

Symptoms of Bowel Obstruction

The symptoms of a bowel obstruction depend on where the blockage sits and how severe it is.

Symptoms of Small Bowel Obstruction

A small bowel obstruction often develops fairly quickly. Common symptoms include crampy pain around the upper abdomen or belly button, nausea and vomiting, and a swollen, bloated abdomen. Some people continue to pass small amounts of wind or loose stool at first, before this stops as the blockage becomes more complete.

Symptoms of Large Bowel Obstruction

A large bowel obstruction usually builds up more slowly. It commonly presents with worsening constipation, lower abdominal cramping and bloating, with vomiting appearing later, if it appears at all. Occasionally, depending on the underlying cause, symptoms can come on suddenly and severely rather than gradually.

Signs That Need Urgent Attention

If abdominal pain becomes constant and severe rather than coming and going, or if it is accompanied by fever, a fast heart rate or a rigid, very tender abdomen, this can mean the blood supply to part of the bowel has been affected. These signs, along with a complete inability to pass wind or a bowel motion, need emergency care straight away. Go to your nearest hospital emergency department, or call triple zero if symptoms are severe, and avoid eating or drinking until you have been assessed.

What Causes Bowel Obstruction?

Common Causes of Small Bowel Obstruction

The most common cause of small bowel obstruction is adhesions, which are bands of scar tissue that can form after abdominal or pelvic surgery and cause a loop of bowel to twist or become trapped. Hernias, where part of the bowel pushes through a weakness in the abdominal wall, are another well recognised cause. Strictures, or narrowed segments, related to Crohn’s disease can also lead to small bowel obstruction, and less commonly, a tumour in the small bowel is responsible.

Common Causes of Large Bowel Obstruction

Bowel cancer is the most frequent cause of large bowel obstruction. Diverticular disease, where small pouches form in the bowel wall and can lead to scarring and narrowing over time, is another common cause. A twisting of the bowel, known as volvulus, can also block the large intestine and needs urgent recognition.

Other and Less Common Causes

Less commonly, a bowel obstruction can be caused by a gallstone that has travelled from the gallbladder into the bowel, a build-up of hardened stool from severe constipation, a swallowed object, or a section of bowel folding in on itself, which is known as intussusception and mainly affects infants and young children. Other causes include hernias in less typical locations and, in some women, endometriosis affecting the bowel wall.

How is Bowel Obstruction Diagnosed?

If a bowel obstruction is suspected, you will usually be assessed in a hospital emergency department. This involves a detailed history and physical examination, along with blood tests to check for dehydration, electrolyte imbalance or signs of infection. Imaging is central to confirming the diagnosis. An abdominal X-ray is often the first test, though a CT scan is generally the most reliable way to confirm the location and likely cause of the blockage and to check whether the bowel’s blood supply has been affected. Ultrasound is sometimes used as well, particularly in children or during pregnancy.

A colonoscopy or sigmoidoscopy may also be used to look directly at the large bowel, and in some circumstances this can help relieve the blockage as well as diagnose it. Capsule endoscopy, which involves swallowing a small camera to examine the small bowel, has a role in some chronic small bowel conditions, but it is generally avoided when an obstruction is suspected, because the capsule itself can become stuck at the site of narrowing.

The Role of the Gastroenterologist in Bowel Obstruction

A gastroenterologist plays a central role in working out what is causing a bowel obstruction and how best to manage it. This includes reviewing your history and symptoms, arranging and interpreting imaging and blood tests, and, where appropriate, performing endoscopy to look directly at the bowel. In some situations, this endoscopic assessment can also be used to treat the blockage. Examples include using colonoscopy to relieve pseudo-obstruction of the large bowel, placing an expandable stent to open up a blockage caused by a bowel cancer, or gently stretching a narrowed stricture caused by Crohn’s disease.

Not every bowel obstruction can be managed this way. A complete obstruction, a closed loop obstruction, or one where the blood supply to the bowel is thought to be compromised is a surgical emergency, and your gastroenterologist will refer you to a general or colorectal surgeon if they expect an operation is needed to relieve it. Where bowel cancer is the underlying cause, your gastroenterologist will also refer you to an oncologist, to plan any further cancer treatment that may be needed. Your gastroenterologist can coordinate these referrals and continues to work alongside these specialists, and alongside your GP, as part of a coordinated team.

How is Bowel Obstruction Treated?

Initial and Non-Surgical Care

Initial treatment in hospital usually involves admission for close monitoring, stopping food and fluid by mouth, and giving fluids directly into a vein to correct dehydration. A tube may be passed through the nose into the stomach to relieve pressure and ease vomiting. Medicines to control nausea and pain are given as needed, and antibiotics may be used if there is a risk of infection. Many partial obstructions, particularly those caused by adhesions, settle with this kind of conservative care over a few days, without the need for surgery.

When Surgery is Needed

Surgery is generally needed for a complete obstruction, a strangulated obstruction where the blood supply is affected, or an obstruction that fails to improve with conservative treatment. The type of operation depends on the underlying cause and may involve removing the affected section of bowel. Your gastroenterologist and surgeon will discuss the most appropriate approach for your situation, along with how to prepare and what to expect during recovery.

Possible Complications of Bowel Obstruction

Left untreated, a bowel obstruction can cut off the blood supply to part of the bowel wall, leading to tissue damage. This can progress to a tear, or perforation, in the bowel wall, allowing infection to spread through the abdomen and potentially leading to sepsis. These complications are uncommon when a bowel obstruction is recognised and treated promptly, which is why urgent assessment is so important whenever the symptoms described above are present.

Can Bowel Obstruction Be Prevented?

Not every bowel obstruction can be prevented, since some causes, such as adhesions after previous surgery, are largely outside your control. There are still steps that can lower your overall risk. Taking part in the National Bowel Cancer Screening Program helps detect and treat bowel cancer and related growths before they cause a blockage. If you live with Crohn’s disease or another inflammatory bowel condition, following your specialist’s management plan reduces the risk of strictures developing. Treating constipation early, staying well hydrated and being gentle in resuming normal eating after abdominal surgery, as advised by your surgical team, are also helpful.

If you have a known narrowing in part of your bowel, your gastroenterologist may recommend a diet lower in insoluble fibre, the tough, rough part of plant foods such as skins, husks and some nuts and seeds, to reduce the chance of food becoming trapped. As Queensland Gastroenterology does not have an accredited practising dietitian on site, if referral to a dietitian is suggested, we recommend using the Dietitians Australia Find a Dietitian directory to find a dietitian who can tailor this advice to your needs.

When to See Your GP or Seek Emergency Care

If you develop sudden abdominal pain together with a complete inability to pass wind or a bowel motion, this needs emergency care, so go to your nearest hospital emergency department without delay and avoid eating or drinking beforehand.

Symptoms are not always this severe. A partial obstruction can still allow some wind or stool to pass while causing ongoing bloating, crampy discomfort or a noticeable change in your usual bowel habit. These milder but persistent symptoms still deserve prompt medical attention rather than a wait and see approach, so see your GP if they continue, come and go, or gradually get worse.

It is also worth seeing your GP if you already live with (or suspect you have) a condition such as Crohn’s disease or diverticular disease, especially if you notice new or worsening symptoms, since these conditions can sometimes lead to narrowing or scarring of the bowel over time. Your GP can examine you, arrange initial tests and, if needed, refer you to a gastroenterologist for further assessment, whether this is your first presentation or a review of an existing condition.

Our specialist team provides comprehensive assessment and ongoing care for patients with bowel obstruction across Brisbane and South East Queensland. Once you have your referral, please contact our practice directly to arrange an appointment.

References

This information has been adapted from the following sources, as at 30/07/2026. It is intended for general patient education and does not replace individual medical advice from your GP or gastroenterologist.

Hopkins C. Large-Bowel Obstruction: Background, Etiology, Pathophysiology. Medscape. Updated 21 July 2026. Available at emedicine.medscape.com/article/774045-overview

Ramnarine M, Pantic D. Small-Bowel Obstruction. Medscape. Updated 2 December 2024. Available at emedicine.medscape.com/article/774140-overview
healthdirect Australia. Bowel obstruction. Reviewed September 2024. Available at healthdirect.gov.au/bowel-obstruction

Dité P, Lata J, Novotný I. Intestinal obstruction and perforation, the role of the gastroenterologist. Digestive Diseases. 2003;21:63-67.

Tai FWD, Sidhu R. Small bowel obstruction: what a gastroenterologist needs to know. Current Opinion in Gastroenterology. 2023;39(3):234-241.