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How is a colonoscopy done?

A thin and flexible tube is inserted through the anus and it slowly advances towards the rectum and bowel. This instrument, called a colonoscope, is as thick as a finger and consists of a lens and a light source that enables images to be observed on a video monitor. It also has a working cannula through which can be introduced auxiliary material to carry out treatments.

For what is a colonoscopy recommended?

A colonoscopy is recommended as a test for the prevention and detection of colorectal cancer, as well as to evaluate symptoms like bleeding or chronic diarrhoea.

How do I prepare for a colonoscopy?

Before the test, the diet recommendations and routines indicated by the health team must be followed because it is essential that the bowel is free from waste in order to visualise the mucosa (lining).

In general, the preparation consists of having a fibre-free diet for 2-3 days before the test, and drinking clear fluids (water only, tea and coffee without milk or cream, clear soup, and carbonated drinks). The test is performed while fasting; therefore, all the previous preparation must be finished 6 hours before.

It is advisable to come accompanied due to the administration of sedation or anaesthesia.

It is a very easy, straightforward test. Moreover, there is no stress and it doesn't cause any discomfort. 

Can I take my medication?

The majority of medications can continue to be taken as usual, but some can interfere with the preparation or the examination. The health team should be informed about the medication that you are taking, in particular products derived from aspirin, anti-inflammatory drugs, anticoagulants (warfarin, dabigatran, apixaban, or heparin), clopidogrel, or other anti-platelet drugs, insulin, or iron. Furthermore, you have to mention any medication allergies.

What happens during a colonoscopy?

The patient must be naked from the waist down and placed on one side or facing upwards on a trolley. In order to visualise the mucosa well, the doctor may introduce gas (air or CO2) into the bowel. In the majority of cases, a rapid elimination general anaesthetic is administered, since the distension of the bowel walls and the advance of the colonoscope, through certain curves or difficult points, can cause abdominal discomfort. A catheter is inserted in a vein of the hand or arm, as well as some electrodes to monitor vital signs.

You will not feel pain during the test. The health professional will slowly advance the colonoscope through the large intestine until it reaches the area that connects the small and large intestine (blind end). Occasionally, the patient is asked to change position (from the side or facing upwards) in order to apply gentle pressure on the abdomen and help the progression of the colonoscope.

As the colonoscope is slowly withdrawn, the bowel lining is examined again. On those occasions when the colonoscope is unable to pass through the entire intestine, an additional test has to be performed.

How long does a colonoscopy last?

The procedure itself generally lasts less than 45 minutes. If the preparation and recovery are taken into account, it lasts between two and three hours.

What happens if the colonoscopy shows something abnormal?

In the cases in which an additional evaluation is needed, an instrument is passed through the colonoscope in order to obtain a biopsy (a small specimen of the bowel lining). Biopsies are used to identify many conditions, and are often performed despite there being no suspicion of cancer.  

When a colonoscope is performed to identify bleeding sites, drugs are injected through the colonoscope or the bleeding vessels are sealed with thermal treatment (cauterisation) or by using small clips.

Polyps can be found during the examination, and it is very possible that they are removed during it.

At first you receive a bit of psycological preparation for what you will have. They insert a tube with a light in your anus, then they look around inside and directly remove any polyps they find. 

What happens after a colonoscopy?

The patient remains under observation until most of the effects of the sedatives or anaesthetics have worn off. For this reason, it is advisable to be accompanied during and after the examination.

It is possible to have cramp or swelling due to the air introduced into the bowel during the examination. These effects usually disappear rapidly when the gas is expelled.

In general, you can eat after the colonoscopy, although in cases in which polyps have been removed (polypectomy), you should follow a special diet and restrict some activities.

It is also normal to have small losses of blood for several days after the procedure.

The health team will explain the test results to you. Normally, you have to wait a certain time to obtain the results of the biopsies.

What are the possible complications of the colonoscopy?

The colonoscopy and the polypectomy are generally safe. A possible complication that could arise is a perforation or a tear of the intestinal wall that could require surgery. You could also bleed in the area where the biopsy was performed or where the polyp was removed, although it is mild. The bleeding can stop by itself or be controlled through the colonoscope. It rarely requires follow-up treatment. Some patients may have a reaction to the sedatives, or a complication of a heart or lung disease. 

Although the complications after the colonoscopy are rare, it is important to recognise the early signs of any complications. In this sense, it is advisable to contact the medical team if you note intense abdominal pain, fever and shivering, or continuous rectal bleeding.

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Substantiated information by:

Maria Pellisé Urquiza

Published: 6 June 2018
Updated: 6 June 2018


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