Step by Step, What Happens During a Colonoscopy

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    Step by step, what happens during a colonoscopy

    In this article, you will learn step-by-step what happens during a colonoscopy. In a colonoscopy, your gastroenterologist will be closely examining your rectum and colon looking for signs of abnormal tissue, sources of bleeding, and inflamed pouches or sections. In order for you to understand what occurs during this procedure, it is important to know about the anatomy of the colon and the rectum. This information may seem overwhelming at first. But, assuredly, with a grasp of the anatomy of your colon before the colonoscopy, you are well-prepared in understanding the complexity of the procedure and in asking your doctor any questions you may have. After the introduction to the anatomy, you will have the opportunity to walk through the procedure with a bird’s eye perspective from pre procedural preparation, the procedure itself,  to the post-procedural process. 

    Anatomy of the Colon and Rectum

    The gastrointestinal (GI)  tract is a long and twisted tube that consists of a series of hollow organs joined from the mouth to the anus. The hollow organs of the GI tract include:

    • Mouth
    • Esophagus 
    • Small intestine
    • Large intestine or colon
    • Rectum
    • Anus

    The colon, or large intestine, is a long (approximately 6 feet) muscular tube that connects the small intestine to the rectum. It’s main function is to process wastes to allow for an easy bowel movement or emptying of the bowels. Other functions of the colon are  to absorb water and electrolytes and digest chemicals with the help of gut microbes.

    The parts of the colon are:

    • Cecum – Pouch-like passage connecting small intestine to colon
    • Ascending colon – Absorbs water from waste
    • Transverse colon – Absorbs water and salts from waste
    • Descending colon – Stores stool to be emptied
    • Sigmoid colon – Contracts to increase colon pressure to move stool into rectum
    • Rectum – Holds stool until evacuation happens

    Stool is the waste left over from the process of digestion after it passes through the small intestine. Stool passes through the colon from a liquid to solid state due to peristalsis – wave-like muscular contractions of the gastrointestinal tract. As the stool moves through the colon, water and salts are absorbed into the intestinal wall. The ascending and transverse sections of the colon have beneficial bacteria that help to break down food into smaller pieces.

     Once the stool reaches the sigmoid colon, it is in solid form and stored until emptied into the rectum for a bowel movement one to two times daily The average time it takes feces or stool to get through the colon is 24-36 hours. 

    The lining of the colon is actually a series of layers that consist of inner linings (mucosa and submucosa), a thick layer of muscle (muscularis propria), and outer layer (serosa).  The mucosa is responsible for absorbing the water from the liquid waste and some nutrients. The mucosa also makes mucus to help the stool move with ease through the colon and rectum. 

    Colonoscopy Equipment

    The colonoscope is the main tool of the colonoscopy procedure. The tool is basically a long flexible tube with a camera attached on one end. The colonoscope has a channel where different surgical instruments can be inserted to be used during the procedure. The instrument has five main components, including:

    • Control section 
    • Instrument channel (where the surgical instruments are inserted)
    • Tip (camera on end)
    • Connection section (connects to power and video)
    • Line (flexible tube of colonoscope)

    What Happens During a Colonoscopy: Detailed Step By Step Breakdown


    Step 1: Check-in                                               5 minutes

    Step 2: Preparation for procedure       15- 20 minutes

    Step 3: Meet with physician                     5-10 minutes                                     

    Step 4: Colonoscopy                               20-45 minutes

    Step 5: Recovery                                           30 minutes

    Step 6: Discharge                                            5 minutes                                

    Pre-procedure: Preparation and Sedation

    Before your colonoscopy, you will be escorted to a private prep room where you will be asked to change into a hospital gown. Your nurse will ask about your current medications, allergies, and your medical history. Then your nurse will place an intravenous (IV) line where you will receive your sedation medicine and fluids. You will also have your vitals measured, including blood pressure, oxygenation content, and heart rate.  


    After your doctor checks in with you to see if you have questions and explain the procedure, you will be taken to the procedure room to be sedated. In the room, you will be connected to a monitor that records your heart rate, blood pressure, and level of oxygenation.  You will be asked to lie down on your left side with your knees bent and pulled up. Your nurse will give you sedation medications.

    During procedure

    The procedure is done with the patient in the left lateral decubitus position or laying down on their left side. 

    The colonoscope is inserted through the patient’s rectum into the colon. The scope is then moved throughout the colon to visualize the lumen (the opening inside the bowels)  and the walls of the colon.

    The gastroenterologist first inspects the region around the anus to check for skin tags, hemorrhoids, prolapse, or anal fistulaw and fissures.A digital rectal examination is also performed and topical anesthetic is applie to lubricate the canal and relax the sphincters. 

    Anal canal: In medicine, an intubation is when a tube is placed in a body cavity. Thus an insertion of the colonoscope in the anus is referred to as an intubation. When the colonoscope is intubated, the gasteroenterologist will inflate the anal canal with air to allow for ease of entry and visualization of the anal region. The anal sphincter restricts the examination of the anus and must be examined once it passes through the canal. 

    Rectum:The rectum is approximately 6 inches or 15 cm long and is easily passed by the colonoscope because it is immobile. 

    Rectosigmoid junction: Gastroenterologists consider this section of the colon challenging because it is such a tight bend. The lumen, or opening, bends significantly and care must be taken to clear the bend and avoid looping the tube of the colonoscope. Once the section is cleared, the descending colon is in clear view and able to be examined and visualized.  

    Sigmoid descending junction (SDC) and sigmoid colon: The S-shaped curve of the sigmoid colon make it the most challenging part of the colonoscopy. There are many folds in the lining of the sigmoid colon which makes it very difficult to visualize the lumen. Thus, the gastroenterologist will add air into the colon and possibly move the patient or colonoscope to allow passage of the tube further up into the colon. In this area, manual abdominal compression may be used and the patient may be moved to ease movement of the colonoscope. 

    Descending colon: After passing through the sigmoid descending junction and the sigmoid region, the gastroenterologist will then move through the descending colon which is a long tube with low mobility. This portion of the colonoscopy usually only takes a few seconds depending on findings (for example, if a polyp or patch of abnormal tissue is found).  

    Splenic flexure: This bend between the descending and ascending colon is the highest portion of the large intestine. It is located just under the diaphragm. If the progression of the colonoscope is difficult, the examiner may move the patient’s position or have an assistant apply abdominal compression.  

    Transverse colon: The opening or lumen of the transverse colon is triangular in shape and is quite mobile. Again, if progression is difficult, an assistant will apply abdominal compression on the umbilical (belly button) area to prevent looping of the colonoscope. 

    Hepatic flexure: This bend of the colon is easy to identify for the examiner and the ascending colon is most often located on the right side. The gastroenterologist will turn the colonoscope to the right while applying air suction. Sometimes, the patient will be placed in the supine (on the back) position to help with progression. 

    Ascending colon: This section of the colon is triangular in shape and has thick folds. It has low mobility, so the examiner can advance the colonoscope easily with a straight push. 

    Cecum: Once the examiner reaches the cecum, the beginning of the colon, the colonoscopy is considered complete. The gastroenterologist will move the colonoscope through the ileocecal valve (the valve between the ileum of the small intestine and the cecum of the large intestine) to confirm that the entire colon was visualized. 


    After the procedure, you will be taken into the recovery room to be observed by medical staff as you regain consciousness. During this time your vitals will be monitored to make sure you are oxygenating properly and that your blood pressure and heart rate are within normal range. The recovery typically takes from 30 minutes to an hour, depending on how sedated you were. Once the medications have worn off you will be allowed a drink of water and pain medication if needed. 

    Who reviews the results?

    Your physician will review the preliminary results of your colonoscopy once you have recovered from the sedation. Because of the nature of the medication, your doctor will most likely not spend too much time explaining the results to you and allow you to recover. Your doctor may send home a print out of the results if you request before the procedure. There are generally two findings from a colonoscopy:

    Negative result. This result is the best outcome of a colonoscopy. Your colon is considered healthy with no abnormal findings. At this point, your physician may want to schedule your future screening. Your physician may also ask you to schedule one sooner than recommended if there were any issues with visualization or if residual waste obscured the view. 

    Positive result. In this case, your physician found a polyp or an abnormal site during the colonoscopy. This is actually quite common and there is no reason to become overly concerned. Most polyps are benign and promptly removed during the procedure. If you had polyps removed during the colonoscopy, your physician will tell you when to expect the results from pathology. The time it takes to receive these results can vary from a few days to a week.

    Post-procedural care and future screenings

    Your recovery from the colonoscopy should take a short time, usually only 24 hours. Your physician will review with you the plan of care in the future depending on the results of the colonoscopy. If you had a negative result, your physician will schedule your next screening based on your age, your health status, and family history of colon cancer. 

    If your physician found a polyp, adenoma (abnormal growth), your physician will discuss with you if you need additional procedures. Sometimes, the examiner is unable to remove all the tissue or there are multiple polyps that require a more extensive colonoscopy. In this case, your physician will develop a plan of action with you for future removal. If the tissue is precancerous or cancerous then you will need additional treatments as well. 


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