|Classification and external resources|
Upright abdominal X-ray demonstrating a small bowel obstruction. Note multiple air fluid levels.
Bowel obstruction (or intestinal obstruction) is a mechanical or functional obstruction of the intestines, preventing the normal transit of the products of digestion. It can occur at any level distal to the duodenum of the small intestine and is a medical emergency. The condition is often treated conservatively over a period of 2–5 days with the patient's progress regularly monitored by an assigned physician. Surgical procedures are performed on occasion however, in life-threatening cases, such as when the root cause is a fully lodged foreign object or malignant tumor.
Signs and symptoms
Tinkly bowel sounds as heard with a stethoscope in someone with a small bowel obstruction.
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Bowel obstruction may be complicated by dehydration and electrolyte abnormalities due to vomiting; respiratory compromise from pressure on the diaphragm by a distended abdomen, or aspiration of vomitus; bowel ischaemia or perforation from prolonged distension or pressure from a foreign body.
In small bowel obstruction the pain tends to be colicky (cramping and intermittent) in nature, with spasms lasting a few minutes. The pain tends to be central and mid-abdominal. Vomiting occurs before constipation.
In large bowel obstruction the pain is felt lower in the abdomen and the spasms last longer. Constipation occurs earlier and vomiting may be less prominent. Proximal obstruction of the large bowel may present as small bowel obstruction.
Small bowel obstruction
Causes of small bowel obstruction include:
- Adhesions from previous abdominal surgery (most common cause)
- Hernias containing bowel
- Crohn's disease causing adhesions or inflammatory strictures
- Neoplasms, benign or malignant
- Intussusception in children
- Superior mesenteric artery syndrome, a compression of the duodenum by the superior mesenteric artery and the abdominal aorta
- Ischemic strictures
- Foreign bodies (e.g. gallstones in gallstone ileus, swallowed objects)
- Intestinal atresia
Large bowel obstruction
Causes of large bowel obstruction include:
- Inflammatory bowel disease
- Colonic volvulus (sigmoid, caecal, transverse colon)
- Fecal impaction
- Colon atresia
- Intestinal pseudoobstruction
- Diverticular disease
- Narcotic induced (especially with the large doses given to cancer or palliative care patients)
Outlet obstruction is a sub-type of large bowel obstruction and refers to conditions affecting the anorectal region that obstruct defecation, specifically conditions of the pelvic floor and anal sphincters. Outlet obstruction can be classified into 4 groups.
- Functional outlet obstruction
- Inefficient inhibition of the internal anal sphincter
- Inefficient relaxation of the striated pelvic floor muscles
- Mechanical outlet obstruction
- Dissipation of force vector
- Impaired rectal sensitivity
- Rectal hyposensitivity
Differential diagnoses of bowel obstruction include:
- Pseudo-obstruction or Ogilvie's syndrome
- Intra-abdominal sepsis
- Pneumonia or other systemic illness.
According to a meta-analysis of prospective studies by the Cochrane Collaboration, the appearance of water-soluble contrast in the cecum on an abdominal radiograph within 24 hours of oral administration predicts resolution of an adhesive small bowel obstruction with a pooled sensitivity of 96% and specificity of 96%.
Some causes of bowel obstruction may resolve spontaneously; many require operative treatment. In adults, frequently the surgical intervention and the treatment of the causative lesion are required. In malignant large bowel obstruction, endoscopically placed self-expanding metal stents may be used to temporarily relieve the obstruction as a bridge to surgery, or as palliation. Diagnoses of the type of bowel obstruction is normally conducted through initial plain radiograph of the abdomen, luminal contrast studies, computed tomography scan, or ultrasonography prior to determining the best type of treatment.
Small bowel obstruction
In the management of small bowel obstructions it was once said, "[n]ever let the sun rise or set on small-bowel obstruction" because about 5.5% of small bowel obstructions are ultimately fatal if treatment is delayed. However improvements in radiological imaging of small bowel obstructions allow for confident distinction between simple obstructions, that can be treated conservatively, and obstructions that are surgical emergencies (volvulus, closed-loop obstructions, ischemic bowel, incarcerated hernias, etc.).
A small flexible tube (nasogastric tube) may be inserted from the nose into the stomach to help decompress the dilated bowel. This tube is uncomfortable but does relieve the abdominal cramps, distension and vomiting. Intravenous therapy is utilized and the urine output is monitored with a catheter in the bladder.
Most people with SBO are initially managed conservatively because in many cases, the bowel will open up. Some adhesions loosen up and the obstruction resolves. However, when conservative management is undertaken, the patient is examined several times a day and X rays are obtained to ensure that the individual is not getting clinically worse.
Conservative treatment involves insertion of a nasogastric tube, correction of dehydration and electrolyte abnormalities. Opioid pain relievers may be used for patients with severe pain. Antiemetics may be administered if the patient is vomiting. Adhesive obstructions often settle without surgery. If obstruction is complete a surgery is required.
Most patients do improve with conservative care in 2–5 days. However, in some occasions, the cause of obstruction may be a cancer and in such cases, surgery is the only treatment. These individuals undergo surgery where the cause of SBO is removed. Individuals who have bowel resection or lysis of adhesions usually stay in the hospital a few more days until they are able to eat and walk.
Small bowel obstruction caused by Crohn's disease, peritoneal carcinomatosis, sclerosing peritonitis, radiation enteritis and postpartum bowel obstruction are typically treated conservatively, i.e. without surgery. Conversely, a small bowel obstruction in a "virgin abdomen" (an abdomen that has not seen an operation) is almost never treated conservatively.
Fetal and neonatal bowel obstructions are often caused by an intestinal atresia, where there is a narrowing or absence of a part of the intestine. These atresias are often discovered before birth via a sonogram, and treated with using laparotomy after birth. If the area affected is small, then the surgeon may be able to remove the damaged portion and join the intestine back together. In instances where the narrowing is longer, or the area is damaged and cannot be used for a period of time, a temporary stoma may be placed.
The prognosis for non-ischemic cases of SBO is good with mortality rates of 3-5%, while prognosis for SBO with ischemia is fair with mortality rates as high as 30%.
Cases of SBO related to cancer are more complicated and require additional intervention to address the malignancy, recurrence, and metastasis, and thus are associated with poorer prognosis.
All cases of abdominal surgical intervention are associated with increased risk of future small-bowel obstructions. Statistics from U.S. healthcare report 18.1% re-admittance rate within 30 days for patients who undergo SBO surgery. More than 90% of patients also form adhesions after major abdominal surgery. Common consequences of these adhesions include small-bowel obstruction, chronic abdominal pain, pelvic pain, and infertility.
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