Answer:
In patients who have had multiple upper GI endoscopies, colonoscopies, barium studies, and RBC scans without identification of the source of blood loss, enteroscopy needs to be performed. Enteroscopy can be performed either with push enteroscopy or wireless capsule endoscopy. The source of bleeding is most likely from AVMs (or angiodysplasias), usually hiding in [...]

Answer:
Portal pressure and variceal size. The portal to hepatic vein pressure gradient must be > 12 mmHg (normal = 3-6 mmHg) for varices to develop. Beyond this level, there is poor correlation between portal pressure and likelihood of bleeding. The best predictor of impending variceal hemorrhage is size. When varices reach a large size (> [...]

Answer:
Elevation of pressure in the hepatic portal system leads to the development of varices. The normal portal venous pressure is ∼ 10 mmHg but increases to > 20 mmHg in portal hypertension. The causes of portal hypertension are classified as presinusoidal, sinusoidal, and postsinusoidal. The most common cause in the Western world is alcohol-related cirrhosis.
Reference:  [...]

Answer:
Usually. The color of stool depends on colonic transit time. If the stool remains in contact with bacteria that degrade hemoglobin, the resulting stool is melanic. Although right-sided lesions are usually associated with melena (dark, tarry stools) and left-sided lesions with hematochezia (the passage of bright red blood per rectum), the opposite can also be [...]

Answer:

Less common causes include

Meckel’s diverticulum
Ischemic or inflammatory bowel disease
Solitary ulcers of the cecum and rectum

Reference: Sleisenger MH, Fordtran JS (eds): Gastrointestinal Disease: Pathophysiology, Diagnosis, and Management, 7th ed. Philadelphia, W.B. Saunders, 2003.

Answer:

Hemorrhoids are the most common cause but rarely present with massive bleeding requiring hospitalization.
Diverticulosis accounts for a significant percentage of cases. Diverticular bleeding may occur from either the right or left colon.
Angiodysplasia or vascular ectasias are among of the more common well-recognized causes in older patients. They are commonly found in the cecum and ascending [...]

Answer:

Elderly patients (age > 60yr)
Patients with fresh blood per NG tube or rectum
Patients who remain hemodynamically unstable despite aggressive resuscitative measures
Patients who have four or more comorbid illnesses (e.g., cardiac disease, liver disease, diabetes) NSAID use

Reference: Sleisenger MH, Fordtran JS (eds): Gastrointestinal Disease: Pathophysiology, Diagnosis, and Management, 7th ed. Philadelphia, W.B. Saunders, 2003.