c l i n i c a l f o l i o s : d i s c u s s i o n

Small Bowel Obstruction



Related narratives: Small Bowel Obstruction, Intestinal Obstruction with Small Bowel Resection, Intestinal Obstruction from Meckel's Band, Intestinal Obstruction with Small Bowel Infarction, Obstructing Small Bowel Primary After Colon Cancer

The most common cause of intestinal obstruction is adhesions from prior surgery. A patient who presents with a complete small bowel obstruction is at risk for strangulation and infarction of the entrapped segment of bowel. There is always a chance that the obstruction will relieve itself, and one should not rush to operate in the absence of peritoneal signs, especially in a patient with multiple prior episodes. Each new operation creates new adhesions, and each operation is more hazardous to the patient. On the other hand, one cannot wait until peritoneal signs appear and a loop of bowel is compromised. Thus one sets a time limit for observation, giving rise to the old surgical adage "never let the sun rise and set on a complete small bowel obstruction".

During the observation period, physical signs give an indication of the patient's status. The initial abdominal X-rays may indicate whether it is a high or low small bowel obstruction by the presence of jejunal loops (distinguished by prominent plicae semicircularis) only, or both jejunum and smooth-walled ileum. In the early stages of obstruction, when most patients present, the patient feels colicy diffuse abdominal pain as teleologically, the bowel contracts violently to overcome the obstruction. This is the response of any hollow viscus to obstruction. On auscultation, there are hyperactive bowel sounds created by the churning of fluid and air within the lumen with each peristaltic rush. The colicy pain induces nausea and vomiting. On palpation, the abdomen is mildly tender diffusely due to stretch on the walls of the dilated bowel, exacerbated by the pressure of the examining hand. It is imperative to pass a nasogastric tube immediately to prevent vomiting and aspiration which can be lethal, especially in an elderly patient. The subsequent role of the NG tube is to prevent swallowed air and gastric secretions from exacerbating the bowel distention.

As time passes on an unrelieved obstruction, the smooth muscle of the bowel wall fatigues and the peristaltic activity decreases. As the bowel becomes atonic, it dilates. The dilated loops are filled with fluid and air. When a drop of fluid falls into a cistern-like loop, there is a high-pitched tinkle heard on auscultation. This high-pitched tinkle should not be confused with the loud early hyperperistaltic rushes. It is a sign of late obstruction. The fatiguing of the bowel is a sign of deterioration of the patient's condition. The return of normal bowel sounds and passage of flatus and stool are signs of resolution.

When a loop of bowel becomes compromised, it undergoes a chain of events. The pressure on the bowel wall and mesentery at the site of obstruction closes off the lowest-pressure channels in the bowel wall first, the lymphatics. One function of the lymphatics is to drain fluid from tissues. With the lymphatics blocked, fluid builds up in the wall of the bowel and the interstitial pressure rises. The next-lowest-pressure channels, the veins, close off subsequently, creating a venous infarct. Since there is still arterial inflow, but no lymphatic or venous drainage, fluid and pressure continue to build. The rising pressure results in ischemia, and finally infarction, as the arteries are compressed and then closed. The end result is tissue necrosis. With necrosis, the bowel wall loses its physical integrity and perforates.

During the course of this process, inflammation progresses in the bowel wall as the body responds to the ischemic insult. The toxic humoral substances released in the course of the inflammatory process cause local peritonitis of the visceral peritoneum, and peritonitis of the parietal peritoneum that the loop is in contact with. This is manifested by local tenderness (visceral peritoneal irritation) and rebound tenderness (parietal peritoneal irritation). When localized tenderness signals a compromised loop, the surgeon has waited too long. The presence of dead bowel increases morbidity dramatically – thus the surgical aphorism. The correct time to operate on a complete intestinal obstruction is before a loop of bowel becomes compromised. Time passed without resolution of the obstruction is the critical decision-maker, not peritoneal signs.

This page was last modified on 10-Feb-2003.