Health News, Information and Advice from a British Doctor

Having a Colonoscopy

Colonoscopy is the endoscopic examination of the large bowel (or colon). The procedure, when complete, should be able to examine the whole of the large bowel from the anus right around to the caecum, where the colon attaches to the end of the small bowel (ileum) at the ileocaecal valve. In many circumstances the colonoscopist is also able to pass the telescope through the ileocaecal valve and enter the last part of the small bowel  (the terminal ileum). Sigmoidoscopy is a more limited examination of the lower half of the colon and is considerably quicker and more easily tolerated.


The colonoscope is just a very long endoscope (up to 1.4m in length) which is slightly stiffer and thicker than the gastroscope, but otherwise has the same functionality with a multi-directional tip, a very bright light, an HD video-chip, a suction channel and water-spray channel (for cleaning the video-chip lens) and an operating channel. Colonoscopy is an extremely important tool for investigating certain conditions that might affect the large bowel (such as diverticular disease, inflammatory bowel disease, polyps or even cancer) and is particularly useful because instruments can be passed through the operating channel of the telescope, which can treat bleeding points, take biopsies and even remove polyps and small cancers. Although other modalities are available for examining the large bowel, such as the old fashioned barium enema or the more modern CT colonogram, it is this latter benefit of the colonoscopic procedure that makes it the ‘gold standard’ investigation. It also offers an alternative to major abdominal surgery for treatment of bleeding areas, removing polyps and small cancers.
Indications for requesting colonoscopic examination of the large bowel are multiple but the commonest are listed below:

  • change in bowel habit (either diarrhoea or constipation or both)
  • bleeding from the back passage
  • excess mucus production
  • abdominal pain (bloating and wind)
  • surveillance because of positive family history of bowel cancer or polyps
  • surveillance because of previous polyps and cancer
  • abnormal result from barium enema or CT colonogram
  • anaemia
  • weight loss and loss of appetite
  • positive result from bowel screening

These latter four indications usually prompt an urgent referral although any of the above symptoms may be indicative of a sinister underlying cause.

The Procedure The bowel has to be completely empty for the procedure to be successful, so laxatives and eperients are usually posted from the endoscopy unit well in advance of the appointment date, along with clear instructions on how to take them and when to starve. Information leaflets are usually included and a consent form may also be included. Different units often offer different types of sedation/pain relief and these would usually be discussed with you on arrival. These include formal sedation, usually with midazolam plus a pain relieving injection such as fentanyl or pethidine, gas and and air (entonox) identical to that given to mums in labour, no sedation at all or just a pain killing injection. The pre-op nurses will check and double check all your personal and medical details prior to entering the examination room and you will be asked to change into a surgical dressing-gown. Consent for the procedure should have been obtained as an outpatient or on arrival. It is generally considered bad practice to obtain this actually within the treatment room. You will be told about the ‘most frequently occurring complications’ which include perforation, haemorrhage and complications of sedation. In reality these are vanishingly rare for straightforward diagnostic colonoscopy. When you enter the room there will be at least 2 nurses to greet you plus one or more doctors, or in more progressive units, a nurse endoscopist and all will be introduced to you. The nurses will run through your details again and then either put a cannula in your arm or instruct you how to use the gas and air. You will be asked to lie on your left hand side and a blood pressure cuff put on your arm, some nasal specs in your nostrils for delivering oxygen and a peg on your finger for measuring oxygen levels in the blood. If you have opted for sedation it will be given now and you probably will have only sketchy memories of the next few minutes, if at all. Colonoscopy can take anything between 15 and 30 minutes. The main sensation experienced by patients is abdominal discomfort and wind. Occasionally this can be severe and may be a reason for terminating the procedure. If you find it very uncomfortable you can request that the examination be stopped in which case an alternative method for examining the bowel may well be organised. If all goes well (and it does in 95% of patients) then the bowel has been completely and successfully examined and you will be moved to the recovery area. During the procedure quite a lot of air is introduced into the bowel, don’t be embarrassed about expelling it, you will be positively encouraged to do so! At this stage the colonoscopist may well want to discuss the findings with you. Any biopsies obtained usually take about a week to process. Special considerations Anticoagulation (Warfarin) and antiplatelet drugs (aspirin and clopidogrel) Unless special therapies or multiple biopsies are intended, it is usually safe to continue these drugs. If you have any doubt or anxieties then phone the unit for advice Diabetes For tablet or diet controlled diabetics then simply abstain from taking the tablets on the morning of the procedure. For insulin controlled diabetics (IDDM) then it is best to phone up the unit and seek advice. Usually these patients are done at the start of the morning lists and simply abstaining from the morning injection (to be given after the procedure) is all that is required but occasionally patients are admitted and put on a drip prior to the procedure. Written by Dr M J Webberley, consultant gastroenterologist August 2015