Lower GI (LGI) bleeding is the loss of blood from the GI tract distal to the ligament of Treitz. LGI bleeding is a common problem in emergency medicine and should be considered potentially life threatening until proven otherwise.

LGI bleeding occurs less often than upper GI (UGI) bleeding, with an annual incidence of approximately 36 per 100,000.¹ Because blood must travel through the UGI tract down to the LGI system, UGI bleeds are the most common source for all causes of blood detected in the LGI system. Among patients with an established LGI source of bleeding (i.e., bleeding past the ligament of Treitz), the most common cause is diverticular disease, followed by colitis, adenomatous polyps, and malignancies.^2,3 LGI bleeding is more common among females and increases significantly in the elderly.¹

About 80% of episodes of LGI bleeding resolve spontaneously.⁴ However, one cannot predict which episodes will spontaneously resolve or which episodes will result in complications. This is partly due to the difficulty in establishing a pathophysiologic diagnosis. In one study, a cause for bleeding was found in <50% of the cases.⁵

Hematochezia is either bright red or maroon-colored rectal bleeding. If hematochezia originates from a UGI source, it indicates brisk UGI bleeding, which may be accompanied by hematemesis and hemodynamic instability. Approximately 10% of hematochezia episodes may be associated with UGI bleeding.⁶ Melena is dark or black-colored stools and usually represents bleeding from a UGI source (proximal to the ligament of Treitz) but may also represent slow bleeding from an LGI source.

DIVERTICULOSIS

Diverticular bleeding is usually painless and results from erosion into the penetrating artery of the diverticulum. Diverticular bleeding may be massive, but up to 90% of episodes will resolve spontaneously. Bleeding can recur in up to half.^7,8 Although most diverticula are located on the left colon, right-sided diverticula are thought to be more likely to bleed.⁹ Elderly patients with underlying medical illnesses, those with increased needs for transfusion, and those taking anticoagulants or nonsteroidal anti-inflammatory drugs have increased morbidity and mortality.⁷

VASCULAR ECTASIA

Vascular ectasia, which includes arteriovenous malformations and angiodysplasias of the colon, is a common cause of LGI bleeding. Vascular ectasia can also be present in the small bowel and is difficult to diagnose. The development of vascular ectasia in the large bowel seems to be due to a chronic process and increases with aging. Inherited conditions can also give rise to arteriovenous malformations. There is also a suggestion that valvular heart disease is a risk factor for developing bleeding vascular ectasias, although this is an area of debate.⁴

ISCHEMIC COLITIS AND MESENTERIC ISCHEMIA

Ischemic colitis is the most common cause of intestinal ischemia and is usually transient. The colon is predisposed to ischemia because of its poor vascular circulation and high bacterial content. Aneurysmal rupture, vasculitis, hypercoagulable states, prolonged strenuous exercise, cardiovascular insult, irriTable bowel syndrome, and certain medications that cause vasoconstriction or slow bowel motility are known risk factors. Diagnosis is usually made by endoscopy. Although most cases will resolve on their own, up to 20% will require surgical intervention.¹⁰

Mesenteric ischemia can lead to bowel necrosis. Causes include thrombosis or embolism of the superior mesenteric artery, mesenteric venous thrombosis, and nonocclusive mesenteric ischemia associated with low arterial flow with vasoconstriction. Diagnosis is difficult, and the presentation can mimic other intra-abdominal pathologies. Diagnosis requires a high index of suspicion, especially in patients >60 years old and in those with atrial fibrillation, congestive heart failure, recent myocardial infarction, postprandial abdominal pain, or unexplained weight loss. CT has a specificity of 92% but only a sensitivity of 64%. Angiography remains the diagnostic study of choice. Despite aggressive treatment, prognosis is poor, with a survival of 50% if diagnosed within 24 hours.¹¹

MECKEL’S DIVERTICULUM

Meckel’s diverticulum consists of embryonic tissue, most commonly found in the terminal ileum. More than half of lesions contain ectopic gastric tissue, which can secrete gastric enzymes, eroding the mucosal wall and causing bleeding. It is a rare but important condition, especially in the younger population.

OTHER CAUSES OF LOWER GI BLEEDING

Numerous other lesions may result in LGI hemorrhage (Table 76-1), including infectious colitis, radiation colitis, rectal ulcers, trauma, and inflammatory bowel disease. Polyps and carcinomas can cause LGI bleeding and are usually a source of chronic anemia. Delayed hemorrhage can occur up to 3 weeks after polypectomy. Patients with left ventricular assist devices are prone to GI bleeding especially due to anticoagulation, risk of arteriovenous malformations, and acquired von Willebrand’s disease.¹² Although hemorrhoids are the most common source of anorectal bleeding, massive hemorrhage is unusual.¹⁰ For further discussion of hemorrhoids, see chapter 85, “Anorectal Disorders.”