Colonoscopy refers to the use of an endoscope to directly view and survey the lower gastrointestinal tract (the terminal ileum, colon and rectum). The colon is first cleansed using purgatives such as Polyethylene Glycol or an oral Fleet preparation, and the procedure is then performed as a day-surgery procedure by a trained endoscopist, who is a gastroenterologist or a surgeon.
Colonoscopies are an important tool in screening for Colorectal Cancer (CRC), and are the gold standard for the early detection of tumours and pre-cancerous polyps. A colonoscopy also has the advantage of allowing the sampling of tissue for histologic confirmation of the diagnosis (looking at the cells under a microscope), and also allows the removal of polyps, sparing the need for open surgery.
The effectiveness of a colonoscopy in screening for CRC depends on a number of factors. Important amongst these are the cleanliness of the colon at the time of endoscopy and the time taken to survey the colon. It stands to reason that if the scope is done carefully in a well-cleansed colon, the likelihood of a) completing a full survey of the colon and b) finding a significant lesion are increased.
The completeness of a colonoscopy is measured by an index known as the caecal intubation rate, the caecum being where the colon begins. Therefore a caecal intubation rate of 100% means that the endoscope could be advanced through the whole length of the colon, allowing for assessment of all the colonic segments. Practically it is impossible to achieve a complete colonoscopy every time, due to the factors explained above, but international norms for a tertiary center are a caecal intubation rate of >90%.
A measure of the success of a colonoscopy is whether it can detect a significant lesion in the colon. Most commonly these are polyps, which are precursors of colorectal cancer. Finding and removing these polyps are important in preventing colon cancer. The rate of detection of these lesions is expressed as the polyp detection rate.
In NUH, the caecal intubation rate and polyp detection rate are tracked using a unique electronic endoscopy record system, with photographic evidence of a successful intubation through to the caecum, and successful removal and retrieval of a polyp.