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Colonoscopy is a procedure where an appropriately trained healthcare professional (some of the best endoscopists are nurses rather than doctors) uses a flexible tube with a light source and camera at one end a video screen at the other to examine the lining of the large bowel, otherwise known as the colon. It is the best currently available way of looking at the lining of the large bowel and compared to other ways of examining the large bowel has the advantage that biopsies can be taken and small polyps (growths in the bowel) can be removed at the same procedure, provided the operator is competent to do so. Occasionally larger or multiple polyps require one or more further procedures.  Diverticular disease is the commmonest finding at colonoscopy. On occasion endoscopists may also look into the last part of the small bowel (known as the terminal ileum) as well. In order to ensure clear views of the bowel and to make completion of the procedure more likely patients are required to clear their bowels using a medication to clean and empty the bowels (Various medications and diets are used). Most endoscopy units will have protocols for this. It may also be necessary to consider carefully the use of certain medications when undergoing this procedure, such as anti-coagulants or blood thinning drugs.

Usually endoscopes are between 9 and 11mm in diameter and approximately 1.5metres long (though the endoscopist may not need to insert all this). Endoscopes tend to have at least one “working channel” and a port for suction (sucking fluid or debris up the scope) and insufflation (blowing air or fluid in so the endoscopist can see where they are going!). This channel can also be used to insert snares, clips and other equipment should they be required. A number of tools are available to make the procedure more comfortable for both endoscopist and patient (Scopeguide and Carbon dioxide are common). Colonoscopy may be undertaken with or without sedation or/and pain relief. Drugs that may be used include nitric oxide (mixed with air), fentanyl and midazolam in various combinations. In the United Kingdom it is unusual to have colonoscopy under general anaesthetic except under specific circumstances.

As one might expect having a tube passed around the large bowel may be uncomfortable. This is particularly the case when loops form within the bowel that cannot be easily resolved. In such circumstances the endoscopist may not be able to reach the whole of the large bowel (We aim to reach the caecum). Typically endoscopists are expected to reach the caecum in at least 95% of cases. It may be useful to know the endoscopists’” caecal intubation rate” prior to embarking on the procedure. As with any invasive procedure colonoscopy is not without some risks. If a polyp is found and removal is undertaken there is approximately a 1 in 150 chance of a significant bleed, which may require the patient to be admitted overnight. In tandem with this polyp removal incurs a 1 in 500 risk of perforation (making a hole in the bowel wall) – whilst these may managed without surgery on occasion surgery is required and this may involve removal of the affected part of bowel. Even without polypectomy colonoscopy does carry a small risk of these adverse events (perhaps one in 2000). It is estimated that endoscopists miss a cancer in 3% of colonoscopies. Missing smaller polyps probably occurs more frequently. More complex interventions like Endoscopic mucosal resection (EMR) and endoscopic surgical dissection (ESD) are often undertaken by advanced endoscopists.

Diagramatic representation of Colonoscopy
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