The primary function of the stomach is to act as a reservoir, initiate the digestive process, and release its contents gradually into the duodenum so that digestion in the small bowel is optimally performed.
Patients with a diagnosis of gastric cancer, trauma, or complicated peptic ulcer disease may require a gastrectomy, which is the surgical removal of a portion of or, on occasion, all of the stomach. The anatomical changes that result after gastrectomy affect the emptying time of the stomach. If the pyloric valve located between the stomach and first part of the small intestine (duodenum) is removed, the stomach is unable to retain food long enough for partial digestion to occur. Food then travels too rapidly into the small intestine producing a condition known as the post-gastrectomy syndrome.
This syndrome is characterized by a lowered tolerance for large meals, rapid emptying of food into the small intestine or “dumping,” abdominal cramping pain, diarrhea, lightheadedness after eating as well as increased heart rate and sharp drops in blood sugar levels. In the "early" dumping syndrome, symptoms occur approximately one-half hour after eating whereas in the “late” dumping syndrome they appear two to four hours after eating. The carbohydrate component draws water into the intestinal lumen causing sudden fluid shifts in the early dumping whereas late dumping is caused by a reactive hypoglycemia. An estimated 25-50% of all patients who have undergone gastric surgery have some symptoms of gastric dumping. The incidence and severity of symptoms are related directly to the extent of gastric surgery.
Complications of post-gastrectomy syndrome include anemia as a result of vitamin B12 or iron malabsorption and osteoporosis. These problems generally occur months or even years after gastric surgery. Vitamin B12 malabsorption occurs when a protein known as intrinsic factor is either not produced by the stomach (this is a condition called pernicious anemia) or when the proximal stomach is resected (the portion of the stomach that produces intrinsic factor). In either case, that absence of intrinsic factor leads to the poor absorption of vitamin B12. Under normal circumstances intrinsic factor binds to vitamin B12 and assists with the absorption of this vitamin in the lower portion of the small bowel. When vitamin B12 is poorly absorbed, anemia and, in some cases, poor nerve function can occur. This generally does not happen for several years because vitamin B12 is stored in large amounts in the liver.
Iron deficiency anemia develops because removal of the stomach often leads to a marked decrease in the production of gastric acid. This acid is necessary to convert dietary iron to a form that is more readily absorbed in the duodenum. Anemia usually does not occur for a few years after gastric surgery because iron is stored in moderately large amounts in the bone marrow, where red blood cells are produced.
Osteoporosis develops as a result of poor calcium absorption, another problem that occurs after gastric surgery. Under normal circumstances, calcium absorption, which occurs in the duodenum and proximal small bowel, is modest at best, with large amounts being lost in the bowel movement. Following gastric surgery, calcium absorption is even less efficient as a result of rapid emptying of the stomach. Calcium also binds tightly to unabsorbed dietary fat which further interferes with its absorption. Symptoms of osteoporosis may develop ten or more years after gastric surgery because of the large amount of calcium that is normally stored in bone.
Treatment of post-gastrectomy syndrome includes initiation of a post-gastrectomy diet, which is high in protein, low in carbohydrates, and low in concentrated sweets. This diet should be consumed as five or six small meals, with limited fluid intake during meals. On occasion, medications may be required to help control these symptoms. Vitamin B12 deficiency can be prevented by providing vitamin B12 shots once each month indefinitely. Oral iron and calcium supplements are often needed to prevent the development of deficiencies in these minerals.