Most intestinal obstruction is due to a mechanical block. Sometimes the bowel does not function, leading to a paralytic ileus. This occurs temporarily after most abdominal operations and with peritonitis. Some causes of intestinal obstruction are shown. Obstruction of the bowel leads to bowel distension above the block, with increased secretion of fluid into the distended bowel. Bacterial contamination occurs in the distended stagnant bowel. In strangulation the blood supply is impeded, leading to gangrene, perforation and peritonitis unless urgent treatment of the condition is undertaken.
The patient complains of colicky abdominal pain, vomiting and constipation without passage of wind. In upper gut obstruction the vomiting is profuse but in lower gut obstruction it may be absent. Examination of the abdomen reveals distension with increased bowel sounds. Marked tenderness suggests strangulation and urgent surgery is necessary. Examination of the hernial orifices and rectum must be performed.
X-ray of the abdomen reveals distended loops of bowel proximal to the obstruction. Fluid levels are seen in small bowel obstruction on an erect film. In large bowel obstruction, the caecum and ascending colon are distended. A water-soluble barium enema may help to demonstrate the site of the obstruction.
Initial management is by nasogastric intubation to decompress the bowel and replacement of fluid loss by intravenous fluids (mainly isotonic saline). Laparotomy with removal of the obstruction is necessary in most cases of small bowel obstruction and if the bowel is gangrenous owing to strangulation gut resection will be required. A few patients, e.g. those with Crohn’s disease, may have recurrent episodes of subacute intestinal obstruction that can be managed conservatively. Large bowel obstruction can often be managed conservatively with a defunctioning colostomy being performed, if necessary. Volvulus of the sigmoid colon can be managed by the passage of a rectal tube to unkink the bowel, but recurrent volvulus may require sigmoid resection.
Rarely the clinical features of obstruction are produced by a condition in which the nerve plexuses of the bowel are damaged – intestinal pseudo-obstruction. This condition is managed conservatively.
Acute intestinal ischaemia
Mesenteric artery occlusion, either from an embolus or from thrombosis in an arteriosclerotic artery, leads to gut ischaemia and, if not dealt with promptly, necrosis of the intestine. The patient presents with severe abdominal pain and vomiting. Bloody diarrhoea is a helpful indicator of the diagnosis but does not occur for some time. The abdomen is usually tender and bowel sounds are absent. The diagnosis must be considered in any elderly patient with arteriosclerotic disease or in patients with atrial fibrillation. Early surgery may prevent gut necrosis but sometimes massive resection of the dead gut is required to save the patient’s life. Mesenteric venous thrombosis occurs mainly in patients who have circulatory failure and can lead to gut necrosis. Often the patient is extremely ill from the underlying condition but surgery may be necessary if the patient is fit enough.