The underlying pathophysiology of colonic ischemia (frequently called “ischemic colitis”) is much like that of ischemia anywhere else in the body: ischemia of the heart (MI), ischemia of the kidney, ischemia of the brain (stroke), etc. The reason it should be called “colonic ischemia” is because not every case of ischemia results in colitis, but the type of injury is the same.
The incidence of colonic ischemia cannot be accurately stated, because so many cases are relatively “meh” or benign. Someone gets some cramping, maybe they pass a little blood in their stool, things get better after a day or two on their own. That makes strongly evidence-based guidelines hard to come by. This is my caveat for the answers below. My source for this post is the 2015 ACG clinical guideline.
But you’re probably wondering, “Do I need to consult GI for every single case of suspected colonic ischemia? Do I need to ask if colonoscopy is indicated for every single patient?”
Appropriate consultation is an art, of course. GI consultation should not be automatic, but for ischemia, which can be vague and multifactorial, never shy away from consulting GI just because “it’ll get better on its own.” A consultant can help identify contributing factors, like meds that should be discontinued, workup for rheumatologic or hematologic disease, suggest other input from cardiology, etc. Think about the following factors:
- How confident are you about the diagnosis? Some cases are slam dunks: cramping abdominal pain, some red stools, double halo sign on CT in a patient with a history of vascular disease. But a lot of these findings are non-specific. The differential includes diverticulitis, IBD, infectious colitis, and even malignancy. If you want to rule out another cause and prove it’s ischemic injury, ask GI about more imaging vs. colonoscopy.
- How severe is the case? Mild cases will likely resolve on their own after a couple of days. Moderately severe cases (see algorithm below) seem most likely to benefit from the additional diagnostic of colonoscopy. Colonoscopy can show the extent of ischemic damage; in particular colonoscopy can visualize right-sided ischemia and pancolitis, which are associated with worse outcomes. As discussed below, anyone with severe findings/peritonitis should NOT have colonoscopy.
- Is this the first time it happened, or is there a pattern of recurrence? If it’s a mild, first-time case, it’s probably not a big deal. Multiple episodes deserve a more detailed workup with endoscopic evaluation and histopathology to prove ischemic injury.
- Are there implications for the future? Because of the differential diagnosis above, consider your patient’s other symptoms, medical conditions, and overall state of health. Would it matter for this particular case whether other types of colitis or masses were excluded?
NB: no prep is indicated for colonoscopy being done for colonic ischemia.
When should colonoscopy NOT be performed? The yield decreases substantially >48 hours after symptoms begin (to about 30%) so colonoscopy won’t be as helpful then. Colonoscopy is not recommended in severe cases, peritoneal signs, or diverticulitis because of theoretical risks of insufflation worsening pressure-related injury or causing perforation.
As a corollary–the ACG guidelines from 2015 also state that there is no evidence to support specific rules on when antibiotics are indicated and how long to give them for. Antibiotics not only prevent bacteremia/sepsis, they probably also help reduce the body’s inflammatory response to bowel injury…but there’s not a whole lot of human studies to show how helpful or unhelpful they are. Therefore, the guideline authors recommend antibiotics that cover bowel flora (like a third-gen cephalosporin + metronidazole) in “moderate” and definitely “severe” cases of colonic ischemia. They suggest 72 hours, but I think if someone is rapidly clinically improving, it’s reasonable to stop antibiotics after 1-2 days.