There are a number of conditions accounting for small and large bowel obstruction. Although a range of pathologies exist, it is important to remember common things are common. There is a clear difference in the origins of pathologies from both the small and large bowel. Colorectal carcinoma is the most common reason for large bowel obstruction, but is relatively rare with the small bowel. Small bowel cancers are mainly those of the caecum causing obstruction at the ileocaecal valve. Progression to obstruction occurs distally in the bowel as the waste contents solidify. Due to the late presentation, metastases are also present at the time of diagnosis in 25% of cases. Volvulus is also seen with bowel obstruction, mainly at the sigmoid colon, seen in the elderly and those with psychiatric illness. Many patients will have had a previous episode. Another frequent cause is ileus which presents post-operatively due to handling of the bowel during abdominal surgery. Obstruction is also a complication of chronic conditions including Crohn’s disease. In females, gynaecological malignancies can cause pseudo-obstruction. Gallstone ileus occurs when a large stone travels into the gut.
The causes of bowel obstruction in children are different. You must consider congenital causes such as meconium ileus seen in neonates with undiagnosed cystic fibrosis. Hirschsprung’s diseaseand intussception should also be excluded.
Causes of mechanical obstruction can be thought of occurring in three subdivisions:
It is also worth considering if the blood supply is compromised, like a strangulated hernia, as this poses further complications and changes the treatment plan to urgent surgical intervention.
Small bowel obstruction is a common presentation for acute abdominal emergencies accounting for up to 80% of cases.
Small bowel obstruction results in a more acute and severe presentation relative to large bowel obstruction. The presenting complaint is commonly central colicky abdominal pain with associated vomitingand abdominal tenderness. Vomiting occurs in proximal obstruction. Dehydration is a common effect with patients requiring fluid management. Tenderness should alert for ischaemic conditions such as strangulated hernia or other forms of complete obstruction. Auscultation reveals the classical high pitched tinkling bowel sounds. You must listen for an appropriate length of time as bowel sounds are absent in paralytic ileus. Later signs include constipation and the presence of a fistula may manifest as foul-smelling faeculant vomiting, anatomically located in the distal bowel.
In cases of severe obstruction, gangrene can develop within hours of ischaemia setting in. Subsequently perforation may occur resulting in shock. In this case signs of shock may be present showing tachycardia, hypotension, cool peripheries and oliguria. Features of peritonism may also be present. This is a serious condition as toxins from the bowel contents can enter the systemic circulation.
Up to 20% of acute abdominal pain presentations are due to bowel obstruction, of which 80% originate from the small bowel.
Large bowel obstruction is less commonly seen than small bowel obstruction. It has a more gradual onset which subsequently leads to its later presentation. It is vital to take a thorough history to reveal any existing chronic conditions as that have the potential complications. From the history it is important to enquire about recent weight loss, changes in bowel habit, rectal bleeding and vomiting (which is a late sign in large bowel obstruction) to exclude the primary diagnosis of bowel cancer. In addition ask about family history of colonic cancer. A long-standing history of constipation may lead to the diagnosis of sigmoid volvulus. The patient may tell you they have had similar less severe experiences previously. On examination there will be significant abdominal distensionand constipationwhich may be confirmed with a PR examination showing an empty rectum. Abdominal tenderness is localised towards the lower abdomen. Auscultation reveals normal bowel sounds.
Managing bowel obstruction is very specific to the cause of the obstruction. As always, conservative management should be considered, but in cases of acute emergencies, surgical intervention may be necessary. Correcting fluid and electrolyte balance is essential if there has been excessive vomiting and there is oliguria (a sign of dehydration). A nasogastric tube can be inserted for in cases of ileus.
Intervention is necessary for acute cases to prevent complications such as perforation and subsequent peritonitis. Hypovolaemia from excessive vomiting or perforation both play a role in circulatory failure there feature of shock should be noted. Oliguria is a good indicator for acute renal failure. In cases of cancer, CT scanning may be needed to stage possible metastatic disease.
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