The small intestine's function is to absorb ingested fluids and nutrients. There are many conditions whose treatment may require removal of a part of the small intestine, most notably cancers, Crohn's disease, a blockade in an intestinal artery, a twisted loop of intestine, an obstruction, and some birth defects. Patients undergoing a resection of half or more of their small intestine are likely to suffer from a myriad of complications known as "short bowel syndrome."
According to the National Digestive Diseases Information Clearinghouse, resection of a large part of the small bowel can lead to deficiencies of various minerals, vitamins, and nutrients. Depending on the section removed of the small bowel, certain deficiencies can occur. The removal of the first part of the small bowel, the duodenum, places the patient at risk for iron deficiency. The removal of the ileum, or the last part of the small intestine, impairs the absorption of vitamin B12 and bile acids, which are essential in digesting dietary fat. Patients who have the middle section, the jejunum, removed suffer from difficulty absorbing proteins, fats, carbohydrates and a few other vitamins.
The Merck Manuals Online Medical Library points out that diarrhea is the main symptom of the short bowel syndrome resulting from the resection of the small intestine. This diarrhea may or may not be associated with abdominal cramping or bloating. The severity of the diarrhea usually decreases as time goes by; at first it is often severe enough that patients are totally dependent on receiving fluids and nutrition by IV, called total parental nutrition. Many patients eventually improve as they adapt to their shortened bowel. Yet, some remain dependent on intravenous nutrition for life. Some patients have diarrhea only after meals, and are thus instructed to change their dietary habits and to break up their large meals into smaller and more frequent meals. These patients are sometimes prescribed the drugs cholestyramine and loperamide one hour before eating.
As noted in the Merck Manuals Online Medical Library, in the early postoperative period, the severe diarrhea could lead to a fatal dehydration because of the extensive loss of water, sodium, and potassium. Patients are, therefore, monitored closely and given rehydrating fluids intravenously.