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How is a Colonoscopy Done?

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Preparation for colonoscopy

The most important aspect of preparation for colonoscopy is obtaining a clean colon to allow optimal examination. We prefer to use polyethylene glycol (PEG)\electrolyte solution (Klean Prep, R) Norgina). This requires the patient to drink four liters of the solution the day prior to the investigation and to remain on a liquid diet until after the examination. Some patients are unable to drink this volume of liquid and in these cases PicolaxR (Nordic) which is a combination of sodium picosulphate and magnesium citrate is used. The first sachet is taken first thing in the morning, on the day prior to examination, and the second in the mid-afternoon. Unlike Klean-Prep, Picolax may result in significant fluid and electrolyte loss and it is essential that the patient maintain adequate fluid intake during the preparation. Frail and elderly patients and in particular, those with significant cardiac disease should be admitted for their bowel preparation. It is also important that patients who are on iron therapy should stop this two to three days before commencing bowel preparation as organic iron tannates produce a sticky black stool which is difficult to clear.

Before admission to the colonoscopy unit the patient should have had verbal and written explanation of the procedure and its possible complications. On admission, the patient is given a further opportunity to ask questions and written consent is obtained. The next step is to secure venous access with a plastic cannula either in the back of the hand or in the forearm. Unless there is a specific contraindication or at the patients request, the procedure is carried out under light sedation. It is important, however, not to over sedate the patient, as it will often be necessary to ask him or her to move during the procedure. Our preferred sedation regime includes diazemuls, starting with between 5 and 10 mg and increasing to a maximum of 20mg and pethidine usually starting with 25 mg going up to a maximum of 50mg. Pulse oximetry is used routinely and low dose (2ml per minute) nasal oxygen is administered if there is any drop in oxygen saturation. Antagonists to benzodiazepines (flumazenil) and opiates (naloxone) should be readily available but are rarely used.

Intravenous hyoscine N-butylbromide (BuscopanR)Boehringes Ingelheim) is used routinely. This is given at the beginning of the procedure and may be repeated during a lengthy examination. There is good evidence that buscopan increases the ease with which the examination can be carried out and the only contraindications are glaucoma and cardiac arrhythmias.


A video colonoscope is used. This incorporates a charged couple device (CCD) chip and supporting electronics in the tip so that a digital image is transmitted to a computer and displayed on a video monitor. This instrument has now largely replaced the earlier fiber-optic instruments. As the video colonoscope does not have an eyepiece it does not need to be held near the endoscopist’s face providing significant advantages, both from a point of view of hygiene and convenience. Control of the tip of the instrument is achieved by pull wires attached at the tip just beneath its outer surface and passing back along the length of the instrument to the angling control wheels in the control head. The up-down wheel is larger and closer to the instrument whereas the right-left wheel is smaller and further away (Figure 1).

Figure 1: Control head of the colonoscope

On the front of the hand piece there are two buttons; depressing the top button provides suction through the biopsy channel whereas the lower button is for air insufflation and washing the lens at the tip of the endoscope. Finger pressure on the hole in the centre of this button provides insufflation and further depression triggers the washing system. The tip of the colono-scope houses the lens to light channels, an aperture for the air-water jet and a suction-biopsy channel (figure 2).

Figure 2: Tip of the colonoscope: note the light channels, the lens for the CCD camera, the washing channel and the suction-biopsy channel

Colonoscopes vary in length and stiffness. We prefer to use a long colonoscope (165-180cm) as this is necessary to reach the cecum in a particularly redundant colon (about 10% of cases). Shorter colonoscopes are available (130-140cm) but have no advantages over the longer instrument. The stiffer colonoscopes tend to be favored by experts, as it is easier to maintain a straight instrument after reduction of a loop. However, if a loop is unavoidable the stiffer instruments cause more stretching and pain and, under these circumstances, a floppier shaft is preferable. Recently, variable stiffness colonoscopes have become available and we consider this to be the instrument of choice.  (figure 3)

Figure 3: Variable stiffness colonoscope: stiffness is varied by rotating the circular hand-piece immediately distal to the head of the colonoscope

Handling of the Colonoscope

The first skill to master is the use of the angling wheels. As the colonscopist’s right hand will be holding the shaft most of the time it is important to develop a technique which allows manipulation of both the up-down wheel and the right-left wheel with one hand. In general, it is best to use the thumb and middle finger to manipulate the wheels leaving the index finger free for the suction and air-water buttons (figure 4). Occasionally, it will be necessary for the endoscopist to take his/her right hand off the colonoscope shaft to allow bimanual manipulation of the controls; this is rarely necessary. Manipulation of the shaft is another very important facet of colonoscopy maneuvering and it should be held approximately 20cm away from the anal margin, preferably between the fingers and the thumb, to allow an easy rolling action for twisting the colonoscope shaft.

Figure 4: position of the hand on the head of the colonoscope: note how the thumb can be moved across to manipulate the left-right control wheel


The procedure starts with the patient in the left lateral position with the knees well drawn up. We give the patient a pair of special disposable shorts with a posteriorly situated aperture, which maintains the patient’s dignity even when asked to move position during the procedure. A rectal examination is carried out to ensure that there is no immediate impediment to the passage of the colonoscope and this opportunity is taken to lubricate the anal margin. The tip of the colonoscope is then inserted and this is best done by placing the tip alongside the index finger and easing the tip sideways through the anal canal (figure 5). The colonoscope is then positioned so that it is coming straight back from the patient and lying in a smooth loop on the trolley. The endoscopist keeps his /her body pressed against the trolley to prevent the colonoscope falling off the side (figure 6). Air is then insufflated into the rectum to obtain a good view and often a pool of irrigation fluid will be seen. The colonoscope should then be twisted so that the pool is lying in the 5 o’clock position in line with the suction channel and the fluid can then be aspirated. This should be done throughout the colonoscopy whenever fluid is encountered, particularly on withdrawal.

From this point onwards there are some basic principles that must be observed to facilitate the examination and minimize any discomfort or danger:

• Steering is usually accomplished by a combination of up-down angulation and torque. Right-left angulation is reserved for fine control.

• When the lumen is not obvious the colonoscope is pulled back and the direction of lumen estimated by the shadowing which indicates the direction of the lumen. It is also important to remember that, when visible, the taenia coli indicate the direction of the lumen (figure 7).

• When steering into a bend, the shaft is twisted until the direction of angulation of the tip is in the twelve or six o’clock position. This provides the maximum range of movement.

• Whenever steering is difficult, movements are carried out very slowly and deliberately; this saves time in the long-term.

• Every attempt is taken to straighten out loops. There are two main reasons for this. Firstly, they are painful and may lead to perforation and secondly, they impede the progress of examination by taking up length and preventing torque from being transmitted to the end of the instrument.

• If a significant resistance is felt, the colonoscope should not be advanced otherwise it may cause perforation either by direct advancement of the tip through the colon wall or from the apex of the loop splitting the colonic wall (figure 8).

• As little insufflation, as possible, is used as this minimizes discomfort and tends to keep the colon shortened and, thereby, easier to intubate.

• If the patient indicates pain, air is aspirated and the colonoscope pulled back. This is because the pain is likely to be due to the stretching of the mesentery by a loop that is increasing in size or to colonic distension.

• If progress is being made but there is some resistance to insertion, further lubrication is applied to the shaft of the instrument.

• Although the procedure almost always starts in the left lateral position, liberal use is made of the supine and right lateral positions, whenever difficulty in negotiating a tight bend is encountered. There are no definite rules but, in general, the usual changes are as follows: recto-sigmoid: to right lateral, sigmoid and descending colon: back to left lateral, splenic flexure: to right lateral, transverse colon: to supine, hepatic flexure: to left lateral.

• On withdrawal of the instrument, air is aspirated every few centimeters in order to make the patient more comfortable at the end of the procedure.

• Although it is useful to think of the colon in anatomical terms, while carrying out the examination, there are no definite luminal landmarks between the anal canal and the cecum. It is, therefore, impossible to be certain how far the colonoscope has progressed along the colon until the cecum has been positively identified.

Rectum and Recto-Sigmoid Junction

Once a good view of the rectum has been obtained it is usually easy to “slalom” around the mucosal folds of the rectum using a combination of torque and up-down angulation until the recto-sigmoid junction is reached. The tip of the colonoscope is then carefully steered into the angle of the recto-sigmoid junction. If a luminal view is not obtained, then pulling back the angled instrument may improve the situation by shortening the colon and straightening the loop that has formed during the initial insertion. If this does not produce a luminal view, it may be necessary to push blindly and allow the tip of the colonoscope to slide past the bend. While this is being done there should be no blanching of the mucosa and the patient should not experience excessive discomfort.

If this maneuver fails, then the patient should be turned onto the right lateral position. This often has the effect of opening up the recto-sigmoid junction and allowing easier passage of the colonoscope. As soon as the lumen is seen again, the colonoscope should be pulled back to straighten the loop which will have formed. It is possible to tell when the shaft of the colonoscope is straight again by feeling a slight resistance and noticing that the tip is starting to slide backwards. It may then be possible to pass directly from the rectum into the descending colon but if there is any significant redundancy of the sigmoid colon a loop is bound to form. This will be one of two configurations, either the “N” loop or the “alpha” loop (figures 9 and 10).

Figure 9: The "N" loop formation by the colonoscope Figure 10: The "alpha" loop formation by the colonoscope

Dealing with Loops in the Sigmoid Colon

The “N” loop is the more common and makes progression of the instrument past the lower descending colon difficult and painful. If this configuration is suspected, the shaft of the colonoscope should be twisted clockwise and withdrawn at the same time until a straight scope is achieved and a luminal view is obtained. The colonoscope should then be advanced while simultaneously maintaining the clockwise twist, in order to prevent the loop from reforming (figure 11). If formation of the loop is preventing the colonoscope from entering the descending colon, and it cannot be reduced by the means indicated above, the assistant should apply pressure in the lower abdomen to attempt to reduce the loop down into the pelvis so that the colonoscope can be passed onwards and around the sigmoid-descending junction, when the withdrawal and twisting maneuver is more likely to be successful. If an “alpha” loop forms during negotiation of the sigmoid colon there is no impediment to the passage of the colonoscope as there is no acute bend and, indeed, if the instrument passes easily through the sigmoid colon it is likely that an “alpha” loop is forming. It is important however that the “alpha” loop should be straightened out eventually, as it limits the maneuverability of the instrument and causes some discomfort. Thus, when the splenic flexure has been passed the colonoscope should be withdrawn usually with a clockwise twist (figure 12). Occasionally, depending on the way in which the “alpha” loop has formed, anticlockwise twist is required. As a general principle, twist on withdrawal of the colonoscope should be applied in the direction, which offers least resistance.

Figure 11: Straightening the "N" loop by a combination Figure 12: Straightening the "alpha" loop by withdrawal
of withdrawal and clockwise torque and clockwise torque after hooking round the splenic

Descending Colon and Splenic Flexure

If the patient has been moved to the right lateral position, in order to facilitate negotiation of the sigmoid colon, the left lateral position should be assumed again for passage up the descending colon. The descending colon is normally easy to pass through but negotiating the splenic flexure, which can usually be recognized as the next acute bend, can present problems. First, the colonoscope tip should be angled around the flexure and once the tip is in the transverse colon the instrument should be withdrawn with a clockwise twist (to eliminate a sigmoid loop). The instrument is then inserted while maintaining the clockwise torque, to overcome recurrent looping. If resistance is felt or if the tip does not progress, then a loop must be forming and hand pressure over the lower abdomen may be of value, as described above.

Transverse Colon and Hepatic Flexure

If difficulty is encountered in negotiating the splenic flexure, the patient should be turned into the supine position or the right lateral position, as this tends to open out the acute angle between the transverse and descending colon. Once the splenic flexure has been passed, the transverse colon is often easy to negotiate and the hepatic flexure is seen as an acute bend. However, in the redundant transverse colon, there may be a very similar bend at its mid-point and when this has been passed it may be difficult to make progress. This is made easier by pulling back frequently, with suction after each small advance, as this will shorten the transverse colon and tend to advance the tip (figure 13). When the hepatic flexure is seen, air should be aspirated to collapse the flexure towards the tip of the colonoscope, which should then be steered around the bend. At the same time, the colonoscope is withdrawn to lift up the transverse colon and push the tip down into the ascending colon (figure 14).

Figure 13: The effect pf pulling back and suction when the colonoscope is in the tranverse colon. This has the effect of reducing the downward looping and advancing the tip

Figure 14: Entering the ascending colon: a combination of pulling back and applying suction tends to drop the tip of the colonoscope into the cecum

Ascending Colon

When the lumen of the ascending colon is seen, suction should be activated again to bring the cecum up to the tip of the colonoscope. If difficulty is encountered in passing the hepatic flexure, and the patient is in the supine or right lateral position, then positioning the patient in the left lateral position will often help. If, on the other hand, the patient is in the left lateral position and the ascending colon has been entered then turning the patient into the right lateral position may allow the colonoscope to move down towards the cecum.

Identifying the Cecum

Identification of the cecum is an essential component of colon-oscopy. It must be emphasized again that, once the anal canal has been passed, it is impossible to say with certainty where in the colon the tip of the colonoscope actually is, from the luminal appearance alone, until the cecum has been reached. Various parameters are used to identify the cecum including the fusion of the three taenia, the appendiceal orifice, visualization of the colonoscope light through the abdominal wall in the right iliac fossa and indentation of the cecum by finger pressure in the right iliac fossa. None of these parameters are adequate, however, as they can be mimicked in other parts of the colon.

It is essential, therefore, to identify the ileo-cecal valve. This takes the form of a bulge on the medial wall of the cecum, about 5cm from the pole and with a large slit at the apex. The slit may be impossible to see owing to the angle of the valve. It can be entered, however, by passing the bulge, angling the tip of the colonoscope in the correct direction and pulling it back along the medial wall of the cecum until the tip impacts in the valve. To do this effectively, it is important to have the ileo-cecal valve either at the 12 o’clock or the 6 o’clock position on the screen, as this permits maximum angulation of a colonoscope. Once the ileo-cecal valve has been intubated, insufflation will distend the ileum revealing a granularity caused by the villi of the small bowel mucosa.

Withdrawal of the Colonoscope

On withdrawal of the colonoscope, careful inspection of the colonic mucosa should be carried out and pools of irrigation fluid should be aspirated so that lesions are not missed. When the tip of the colonoscope has been pulled back into the rectum, it is often useful to carry out a retro-flexion maneuver, in order to visualize the distal rectum around the anal canal. This involves fully retroflexing the instrument with the up-down wheel and pushing it gently back into the rectum with either clockwise or anticlockwise twist (figure 15).

Figure 15: Retro-flexion is necessary to obtain a view of the distal rectum and upper anal canal


A video of a colonoscopy


The main complications of colonoscopy are perforation, bleeding, infection and hypotension.


Perforation can be caused by rough handling of the endoscope and pushing against undue resistance, as described above. More commonly, however, it is due to endoscopic snaring of a broad based polyp. Occasionally, perforation can occur because of insufflation of air into a thin walled diverticulum and it is essential, when colonoscoping a patient with diverticular disease, to avoid pushing the tip of the instrument into the mouth of a wide necked diverticulum. Patients should always be warned about the possibility of perforation, particularly if polypectomy is envisaged.

If frank perforation into the peritoneal cavity is noted at the time of colonoscopy, then the patient should go for immediate surgical repair. If perforation is suspected, then a water soluble contrast enema should be carried for confirmation. Again, if there is free leakage of contrast into the peritoneal cavity, repair is indicated. Conservative treatment of large colonic perforations is highly dangerous; when perforation occurs during colonoscopy with a well-prepared bowel little peritoneal contamination occurs and there is a window of opportunity to repair the perforation with minimal morbidity. Taking an expectant approach is likely to lead to abscess formation or generalized peritonitis.


Bleeding is nearly always the result of polypectomy and patients should be warned about this possibility. It may occur at the time of polypectomy or may be delayed for up to 14 days after polypectomy. Management of such bleeding is outside the scope of this article but patients who are on aspirin should have this stopped 7 to 10 days before colonoscopy and polypectomy. If the patient is on anti-coagulate medication this must be controlled, as for any surgical procedure, if polypectomy is anticipated.


It is known that colonoscopy can lead to bacterium and prophylactic antibiotics should be used for patients with prosthetic heart valves, a prior history of endocarditis, a synthetic vascular graft less than one year old and surgically constructed systemic-pulmonary shunts. Occasionally, gram negative septicemia can result from colonoscopy and unexplained pyrexia or collapse should be managed with blood cultures and antibiotics.


Bradycardia, hypotension and cardiorespiratory arrest can be induced by over sedation and vagal stimulation from the instrumentation. If the patients develops a profound bradycardia during colonoscopy the investigation should be terminated and the use of atropine considered.


Colonoscopy is a challenging procedure and consistent success requires intensive training and practice. It must be remembered, however, that a 100% cecal intubation rate is not feasible, even in the best of hands. The colonoscopist must be prepared to abandon a procedure, particularly when it becomes clear that the sigmoid colon is very sharply angled in the pelvis. This will probably be due to a combination of adhesions and diverticular disease and persistence in this situation may well lead to perforation. Nevertheless, a total colonoscopy rate in the region of 90% s should be achievable. The new generation of virtual reality colonoscopic trainers may well hasten the training process. Another innovation, which may facilitate training, is the new magnetic imager, which allows the endoscopist to visual-ise the shape of the colon.6 There is, however, no substitute for clinical experience, and if a trainee in gastrointestinal surgery wishes to have colonoscopy as part of his/her repertoire, intensive, focused hands-on training is required. There is no place for an occasional colonoscopist, and a trainee should not expect to be competent until 500 examinations have been performed under direct supervision.


1. Winawer SJ, Stewart ET, Zauber AG et al. Accuracy of colonscopy and double contrast barium enema for surveillance after polypectomy. N Engl J Med 2000; 342: 1523-1524
2. Lieberman DA, Weiss DG, Bond JH, Ahnen DJ, Gdenal H, Chejfec G. Use of colonoscopy to screen asymptomatic adults for colorectal cancer. Veterans Association Co-operative Study No 380 N Engl J Med 2000; 343: 162-165
3. Towler BP, Irwig L, Glasziou P, Weller D, Kewenter J. Screening for colorectal cancer using the faecal occult blood test, haemoccult. Cochrane Database Syst Rev 2000; (2): CD001216
4. Saunders BP, Williams CB. Premedication with intravenous antispasmodic speeds colonic insertion. Gastrointest Endosc 1996; 43: 209-211
5. Brooker JC, Saunders BP, Shah SG, Williams CB. A new variable stiffness colonoscope makes colonoscopy easier: a randomised controlled trial. Gut 2000; 46: 801-805
6. Shah SG, Brooker JC, Williams CB, Thapar C, Saunders BP. Effect of magnetic endoscope imaging on colonos-copy performance: a randomised controlled trial. Lancet 2000; 356: 1718-1722


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