Chapter 6 Acute Lower Gastrointestinal Bleed
Definition
The passage of maroon stools is typical of a right colonic bleed, while the passage of bright red blood tends to occur with a left colon source. However, a patient may also pass bright red blood per rectum with a brisk upper GI bleed.
Etiology
A prospective study from 2001 assessed the relative frequencies of the various causes of severe hematochezia (Table 6-1). A colonic source was found in 81% of cases, an upper GI source in 15%, and a small bowel source in 1%. The remainder of cases did not have a source found on investigation. Other studies show slightly different ranges for patients with hematochezia (Table 6-2).
Table 6-1 Causes of Severe Hematochezia
| Cause | Percent |
|---|---|
| Colon | |
| Diverticulosis | 24.0 |
| Internal hemorrhoids | 11.3 |
| Ischemic colitis | 10.0 |
| Rectal ulcers | 7.4 |
| Inflammatory bowel disease or other colitis | 6.6 |
| Post-polypectomy bleed | 6.0 |
| Colonic neoplasm | 5.0 |
| Colonic angiomas or radiation telangiectasias | 4.6 |
| Other | 6.1 |
| Total colon | 81.0 |
| Upper GI source (esophagus, stomach, duodenum) | 15.3 |
| Small bowel source | 1.3 |
| No source identified | 2.4 |
| Total non-colon | 19.0 |
| Total | 100.0 |
Table 6-2 Causes of Hematochezia
| Cause | Percent |
|---|---|
| Diverticulosis | 17–40 |
| Arteriovenous malformations | 2–30 |
| Colitis | 9–21 |
| Ischemic, infectious, radiation or inflammatory | 10 |
| Neoplasia, polyps, or post-polypectomy bleeding | 11–14 |
| Hemorrhoids, rectal varices | 4–10 |
| Upper GI source (proximal to Ligament of Treitz) | 0–11 |
| Small bowel source | 2–9 |
Diverticulosis is the most common cause of moderate to severe hematochezia, accounting for roughly one third of cases of brisk lower GI bleeds. The prevalence increases with age, from 30% at age 60 to 65% at age 85. Risk factors for diverticular bleeding include use of nonsteroidal anti-inflammatory drugs, constipation, and older age. Although diverticulosis usually occurs in the left colon, diverticula in the right colon account for the majority of cases of diverticular bleeding. The source of bleeding is arterial, and usually painless; some patients may experience mild abdominal cramping due to colonic spasm.
Colorectal Polyps and Cancer
Studies estimate that colorectal polyps and cancer account for roughly 20% of lower GI bleeds, slightly more if post-polypectomy bleeds are included as well. Colorectal polyps or cancer usually do not cause severe hematochezia, but rather, occult GI bleeding or intermittent mild hematochezia. Patients with colorectal cancer may have other associated signs and symptoms, including weight loss, constipation, or change in bowel habits. Bleeding results from erosions and ulcerations that develop from the friable mucosa. Although polyps may be removed endoscopically, treatment of colorectal cancer usually requires surgery.
Post-polypectomy bleeding may occur up to one week after the procedure, and is treated endoscopically.
Colitis
Inflammatory bowel disease and, in particular, ulcerative colitis, may present with hematochezia. Most patients will have other associated signs and symptoms, including abdominal pain, cramping and tenderness, fevers or chills, and increased white blood cell count.
Ischemic colitis typically presents with subjective pain out of proportion to physical findings. Moderate hematochezia usually occurs within 24 hours of pain onset.
The most common bacterial causes of hematochezia are Shigella, Campylobacter, Salmonella, and Enterohemorrhagic E. coli. Clostridium difficile infection may also cause hematochezia. In immunocompromised patients, cytomegalovirus infection should also be considered. Infectious colitis is unlikely to cause severe or massive bleeding.
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