Overall, colonoscopy is a very safe test, but as with any medical procedure, complications are possible. Studies have estimated the overall risk of complications for routine colonoscopy to be extremely low, at approximately 0.35 percent. During colonoscopies where a polyp is removed (a polypectomy), the risk of complications has been higher, although still very uncommon, at up to 2.3 percent. In contrast, the lifetime risk for developing colon cancer is about 6 percent. Complications during a colonoscopy can include perforation, bleeding, postpolypectomy syndrome, reaction to anesthetic, and infection.
Before a colonoscopy, it is important to clean the bowel properly so that the physician doing the test can pass the instruments through the colon and get a good visual of the colon wall. Complications during the prep for a colonoscopy are uncommon, but can occur, particularly in elderly patients, or in those with congestive heart failure.
A perforation is a tear or a hole in the intestine. The risk of perforation is very low after a colonoscopy is used to make a diagnosis, and is only slightly higher after a colonoscopy during which a polyp is removed. A perforation can occur if an instrument punctures a thin point in the colon wall, or if the air introduced into the colon during the test causes excessive distention.
A large, visible perforation is considered an emergency and is treated through surgery to close the tear. In some cases with smaller tears that are found early, surgery may not be needed, and the perforation may be treated with bowel rest, antibiotics, and careful monitoring.
Bleeding occurs in about 1 out of every 1,000 colonoscopy procedures. The bleeding may be treated during the test, but in most instances, bleeding will resolve on its own. When a polyp is removed, there is a 30 to 50 percent chance that bleeding will occur anywhere from 2 to 7 days after the colonoscopy. This type of bleeding may also resolve on its own, but may require treatment if it is severe.
This is a syndrome that occurs as a result of a burn to the bowel wall during polyp removal. As a reaction to polypectomy, anywhere from 12 hours to a few days later, a patient develops fever, abdominal pain, and an elevated white blood cell count. after a colonoscopy. The risk of postpolypectomy syndrome after a colonoscopy during which a polypectomy was done is very low. Treatment may include rest, intravenous fluids, and antibiotics.
Effects from Anesthetic Medications:
Sedating medications, often called "twilight sleep," are given during a colonoscopy in order to make patients more comfortable. There are risks, such as an allergic reaction or respiratory problems, any time sedatives are given. During a colonoscopy, there is a very small risk of a serious respiratory effect from medications. Other risks from sedatives include a reaction at the injection site, nausea, vomiting, and low blood pressure.
Infection after a colonoscopy is very rare. An infection can be transmitted between patients if the endoscope is not cleaned and sterilized properly between tests. The risk of this happening, however, is very low.
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ASGE. "Complications of Colonoscopy." American Society for Gastrointestinal Endoscopy 2006. 28 Aug 2013.
Wayne JD. "Postpolypectomy electrocoagulation syndrome." UpToDate 11 Jan 2013. 28 Aug 2013.