Gastrointestinal bleeding.

Exsanguinating hemorrhage often results from a duodenal ulcer penetrating the posterior wall. If the patient's condition does not stabilize after replacement of 25 percent of the blood volume, surgery must be undertaken immediately. For the patient who presents in shock but becomes stable with volume replacement, endoscopy or arteriography may be performed, depending on the presumed site of bleeding. Drainage from the nasogastric tube is the most important indicator of the site of bleeding.