Colonoscopy

A colonoscopy is a direct look at the lining of the large intestine. A flexible tube about the thickness of a finger, carrying a camera and a light at its tip, is passed through the anus and steered around the whole length of the colon to where it joins the small intestine. The images appear on a screen in high definition and your doctor examines the lining carefully on the way back out.

It does more than look. Instruments passed down a channel in the tube allow your doctor to take small samples of the lining for the laboratory, to remove growths from the wall, to stop a point that is bleeding, and to stretch a narrowed segment. Removing a growth at the time it is found is the reason the test is done as often for prevention as for diagnosis.

How much of the lining is actually seen depends almost entirely on how clean the bowel is. Preparation is the part patients do themselves and the part that determines whether the examination is worth having, so the instructions about the laxative and the fluids are worth following precisely.

The preparation starts a day or two before. You move to a low-residue diet, then to clear fluids only, and you drink a large volume of laxative solution in divided doses, usually one the evening before and one early on the morning of the test. It will keep you near a toilet for several hours and the end result should be clear or pale yellow fluid. Chilling the solution and drinking it steadily through a straw makes it more tolerable. You may take clear fluids up to two hours before the appointment, and your doctor will tell you what to do about blood thinners, diabetes medication and iron tablets, all of which need specific instructions.

On the day, a cannula is placed in your hand and sedation is given through it. You are drowsy or asleep and most people remember little or nothing. You lie on your left side with your knees drawn up. Gas is used to open the bowel out so it can be seen, and carbon dioxide is used in most units because it is absorbed quickly and leaves far less bloating.

The examination takes 20 to 45 minutes and longer where growths are removed. You then rest in the recovery area for an hour or so while the sedation wears off, and go home the same day. You must have a responsible adult to take you home.

Expect cramping and wind for a few hours as the gas clears, and walking about helps it. You can eat normally once you are fully awake, starting light, and drink plenty of fluids to make up for what the preparation took out of you.

Sedation stays in your system longer than it feels like it does. For the rest of the day do not drive, do not operate machinery, do not sign anything legally binding and do not be alone at home if it can be avoided. Most people are back to normal the following morning and at work the next day.

If growths were removed, you will be told to avoid heavy lifting and strenuous exercise for a few days and given specific advice about when to restart blood-thinning medication. A little fresh blood on wiping in the first day or two is common after a removal. Samples sent to the laboratory take about a week, and your doctor will tell you before you leave what was seen and when the follow-up interval should be.