How is a colonoscopy performed?

How is a colonoscopy performed?

How is a colonoscopy performed?

Colonoscopy consists, thanks to a flexible endoscope, in observing the interior of part of the intestines and, if necessary, performing biopsies and treatment. It requires specific preparation of the digestive tract, then hospitalization for a few hours.


Colonoscopy is the observation of the inside of the large intestine (colon) and the end of the small intestine. This examination is carried out using an endoscope (flexible tube equipped with a small camera, a lamp, and, if necessary, surgical instruments passing through the channel of the endoscope). This instrument allows:

  • observe the inner lining of the intestine in search of abnormalities,
  • to carry out samples and treatment, if necessary:
    • performing biopsies
    • removal of colon polyps
    • coagulation of small lesions of blood vessels.

Colonoscopy is the reference examination for the diagnosis of colon diseases (colon polyps, colorectal cancer, Crohn’s disease, ulcerative colitis, etc.) It is prescribed when there are digestive symptoms ( rectorrhagia, presence of black blood in the stool, recent constipation, abdominal pain …) or after a positive screening for colorectal cancer.


Colonoscopy is performed under general anesthesia or sedation (light anesthesia). This is why a consultation with an anesthesiologist is mandatory, eight to ten days before the examination.

During the colonoscopy, the doctor observed in detail different parts of the intestine. They must therefore be perfectly clean, without any fecal matter. This is why you are asked to follow a diet without dietary fiber (or “without residue”), generally the day before and sometimes two days before the exam. In this context, certain dishes are to be avoided (green vegetables, raw vegetables, salad, dairy products, raw fruits), and your meals are limited to a few types of food:

  • broths without vegetables;
  • incomplete pasta;
  • potatoes;
  • meat;
  • fish;
  • cooked fruit compotes;
  • Whitebread.

To be able to comply with this regime, it is preferable to postpone any business or leisure trips during the days concerned.

To finish cleaning your bowels, your doctor will prescribe a bowel prep liquid. This is a product to be ingested once or twice, the day before and/or a few hours before the examination, depending on the prescription. This drug quickly causes very significant diarrhea, without abdominal pain.

Finally, on the day of the colonoscopy, it is necessary to arrive on an empty stomach. Therefore, do not take any food, drink, or medication from the time set by the anesthesiologist (generally six hours before the examination for solid foods and three hours for liquids). You are also asked not to smoke during this time (tobacco increases gastric secretions).

If you are taking medication, it is important to inform the anesthesiologist during the pre-anesthesia consultation: indeed, their effect can be modified by the preparation of the colon. Follow the instructions given to you carefully.


Colonoscopy is performed in a hospital or clinic by a gastroenterologist. It gives rise to hospitalization for a few hours (we speak of ” outpatient surgery “).

The examination consists of several stages:

  1. You are installed in a room or a box, equipped with a bed or an armchair. There, you undress and put on the attire required to enter the operating room (stupid gown, cap, and slippers).
  2. You are taken to an operating theater equipped with anesthetic monitoring devices, and anesthesia is performed.
  3. The doctor introduces, through the anus, the endoscope (flexible tube equipped with a small camera, a lamp, and, if necessary, surgical instruments passing through the channel of the endoscope). To unfold the walls of the intestine to observe them well, the air is blown through the tube.
  4. The gastroenterologist looks inside the colon and part of the small intestine through the camera. If necessary, he takes samples and treatments.
  5. The colonoscope is gently withdrawn, and the insufflated air is aspirated.
  6. You are taken to the recovery room, and you wake up from the anesthesia within minutes. There, we monitor your blood pressure, your breathing, and your general condition (including the absence of pain, and discomfort), for about an hour.
  7. The gastroenterologist who performed the colonoscopy reports his observations to you. If he has taken samples, the results will be communicated to you a few days later.
  8. We bring you back to your room or your cubicle to continue monitoring for a few hours. You are also served a snack. At this stage, you may feel abdominal bloating without pain, due to the persistence of gas in the digestive tract. This passes with the emission of this gas through the anus.
  9. You leave the establishment. Due to the effects of anesthesia:
    • it is mandatory to be accompanied by a relative (relative or friend);
    • Driving a vehicle is prohibited on the day of the intervention.

After each examination, the endoscope is disinfected and the accessories used are sterilized (biopsy forceps, etc.) or discarded in the case of single-use equipment, according to defined procedures, to prevent possible transmissions of infections.


The day after the exam, you can resume your activities without difficulty.

In very rare cases, complications may occur perforation of the digestive wall, digestive hemorrhage, etc. In the event of any abnormal symptom (eg abdominal pain, emission from the anus of red blood, abnormally black stools, fever), quickly consult your doctor.