What happens during a colonoscopy?

Walter J. Coyle, MD
A colonoscopy is used to detect cancer or precancerous polyps in the colon and diagnose other gastrointestinal issues. During the procedure, you will be sedated and the gastroenterologist will insert a colonoscope through the rectum. The doctor uses the colonoscope to view the upper and lower colon. If the colonoscope reveals any suspect tissue, it can be removed and biopsied. Your physician can also remove precancerous polyps; this will decrease your risk of developing full-blown colorectal cancer. The procedure itself usually takes less than an hour. Because you are sedated, you won’t likely feel anything during the procedure.

After the colonoscopy, you won’t be allowed to drive because of the sedation. Most outpatient facilities will not even allow you to check in unless you have arranged for someone to drive you home. You may also want to avoid driving for about 24 hours, but unless your physician advises you otherwise, you can resume your normal activities.
Colonoscopy is typically well-tolerated and rarely causes much pain. You might feel pressure, bloating or cramping during the procedure. Typically, your doctor will give you a sedative or painkiller to help you relax and better tolerate any discomfort. You will lie on your side or back while your doctor slowly advances a colonoscope (a thin flexible tube with a lens and light source allowing your doctor to view images on a video monitor) along your large intestine to examine the lining. Your doctor will examine the lining again as he or she slowly withdraws the colonoscope. The procedure itself usually takes less than 45 minutes, although you should plan on two to three hours for waiting, preparation and recovery. In some cases, the doctor cannot pass the colonoscope through the entire colon to where it meets the small intestine. Your doctor will advise you whether any additional testing is necessary.
If your doctor thinks an area needs further evaluation, he or she might pass an instrument through the colonoscope to obtain a biopsy (a small sample of the colon lining) to be analyzed. Biopsies are used to identify many conditions, and your doctor will often take a biopsy even if he or she doesn’t suspect cancer. If colonoscopy is being performed to identify sites of bleeding, your doctor might control the bleeding through the colonoscope by injecting medications or by cauterization (sealing off bleeding vessels with heat treatment) or by use of small clips. Your doctor might also find polyps during colonoscopy, and will most likely remove them during the examination. These procedures don’t usually cause any pain.
Polyps are abnormal growths in the colon lining that are usually benign (noncancerous). Your doctor can’t always tell a benign polyp from a malignant (cancerous) polyp by its outer appearance, so it will usually be removed for analysis. Because cancer begins in polyps, removing them is important in preventing colorectal cancer.
Your doctor may destroy tiny polyps by fulguration (burning) or by removing them with wire loops called snares or with biopsy instruments. Your doctor will use a technique called "snare polypectomy" to remove larger polyps by passing a wire loop through the colonoscope and remove the polyp from the intestinal wall using an electrical current. You should feel no pain during the polypectomy.
Afterwards, you will be monitored until most of the effects of the sedatives have worn off; someone must drive you home and stay with you.

When the patient arrives, an intravenous drip feed is placed. The patient receives conscious sedation ("twilight sleep") and then the colonoscope is inserted to the end of the colon. All lesions are removed and the whole procedure typically takes 30 to 40 minutes.

Daniel Labow, MD
Surgical Oncology
The day before the colonoscopy, you take a bowel preparation to clean out the colon and fast after midnight before the test. Then, an iv is started and sedation given. The test then takes place and lasts less than 30 minutes in most cases. You might feel a little groggy after the test for a few hours but can resume all normal activities that day. 
You’ll lie on your left side while the doctor inserts the colonoscope into your rectum.  A camera at the tip of the colonoscope sends images to a monitor so the doctor can look closely at the inside lining of your colon. The scope puts air into your colon to inflate it and give the doctor a better view.
Your doctor can also insert instruments through the colonoscope to remove polyps, take tissue samples, inject solutions, destroy abnormal tissue, or help widen openings.
A colonoscopy itself usually takes about 30 minutes, but may take longer if a polyp is found and removed. Before the colonoscopy begins, you will be given a sedating medicine (usually through your vein) to make you feel comfortable and sleepy during the procedure. You will probably be awake, but you may not be aware of what is going on and may not remember the procedure afterward. Most people will be fully awake by the time they get home from the test.
During the procedure, you will be asked to lie on your side with your knees flexed and a drape will cover you. Your blood pressure, heart rate, and breathing rate will be monitored during and after the test.
Your doctor should do a digital rectal exam (inserting a gloved, lubricated finger into the rectum), before inserting the colonoscope. The colonoscope is lubricated so it can be easily inserted into the rectum. Once in the rectum, the colonoscope is passed all the way to the beginning of the colon, called the cecum. You may feel an urge to have a bowel movement when the colonoscope is inserted or pushed further up the colon. To ease any discomfort it may help to breathe deeply and slowly through your mouth. The colonoscope will deliver air into the colon so that it is easier for the doctor to see the lining of the colon and use the instruments to perform the test. Suction will be used to remove any blood or liquid stools.
The doctor will look at the inner walls of the colon as he or she slowly withdraws the colonoscope. If a small polyp is found, the doctor may remove it. Some small polyps may eventually become cancerous. For this reason, they are usually removed. This is usually done by passing a wire loop through the colonoscope to cut the polyp from the wall of the colon with an electrical current. The polyp can then be sent to a lab to be checked under a microscope to see if it has any areas that have changed into cancer.
If your doctor sees a larger polyp or tumor or anything else abnormal, a biopsy may be done. For this procedure, a small piece of tissue is taken out through the colonoscope. The tissue is looked at under a microscope to determine if it is a cancer, a benign (non-cancerous) growth, or a result of inflammation.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.