Intestinal obstruction results from any disease or process that impedes the normal passage of contents. It may be acute, subacute, chronic or acute on chronic.
The common causes vary according to age. Neonatal obstruction may result from a meconium ileus, an atresia of the small or large bowel, a malrotation or Hirschsprung disease. Children develop intestinal obstruction from external hernia, intussusception or surgical adhesions. In adults external hernia, large bowel cancer, adhesions, diverticular disease and Crohn’s disease may all cause obstruction.
The bowel may obstruct from an intraluminal mass, a mural problem or extramural compression. These result in a simple obstruction. The bowel above the lesion becomes progressively distended resulting in painful stretching. There may be compression of blood vessels and a consequent ischaemia.
In a volvulus, malrotation or hernia there may be strangulation. There is occlusion of the low-pressure veins resulting in congestion and oedema. As the extracellular pressure rises arteries become obstructed causing ischaemia and infarction.
Patients present with pain, vomiting and a failure to pass faeces or flatus. The site of pain is dependent on the embryological gut:
· Foregut (stomach to half way along the second part of duodenum). Pain is felt in the epigastrium.
· Midgut (until two thirds of way along the transverse colon). Pain is felt in the umbilical region.
· Hind gut (down to the dentate line of the rectum). Pain is felt in the suprapubic region.
Physical examination reveals abdominal distension, possibly visible peristalsis. Auscultation reveals exaggerated bowel sounds and high pitched tinkling sounds when bowel becomes distended with fluid or gas.
Obstruction may progress to perforation and peritonitis.
In a volvulus there are two points of obstruction. Similarly in proximal colonic obstruction the ileocaecal valve forms a second point of obstruction. A closed loop obstruction therefore results with rapid compromise of blood supply and high risk of strangulation.
Abdominal X-ray reveals the distension and allows assessment of the position within the bowel. Small bowel has markings that cross the whole bowel diameter (valvulae conniventes) whereas large bowel markings (haustra) only partially extend across the diameter. Erect abdominal X-ray may demonstrate fluid levels and any coexistent perforation.
Following resuscitation, prompt diagnosis and operation are essential to avoid strangulation. Nil by mouth, NG suction and i.v. fluids are used in non-surgical causes or patients unable to tolerate procedures.
Hernias are reduced and repaired, adhesions and bands are divided.
Lesions within the bowel wall such as tumours require resection with end-to-end anastomosis.
Gallstones or food bolus causing intraluminal obstruction are milked into the colon.
Strangulated bowel is resected and an end-to-end anastomosis performed.
Right colonic obstruction:
Obstructive lesions of the right colon are managed by right hemicolectomy and end-to-end ileocolic anastomosis.
Palliative side-to-side anastomosis between the ileum and transverse colon is performed in cases of inoperable tumours.
Left colonic obstruction: Surgery is often a two-stage procedure to reduce the risk of anastomotic leakage.
Resection of bowel with both ends exteriorised or a Hartman’s procedure (a defunctioning colostomy with closure of the distal stump, which is returned to the abdominal cavity).
Restoration of continuity at elective surgery some weeks later.