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How Colonoscopy is Done
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.
Equipment
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
Procedure
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
flexure
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
COMPLICATIONS OF COLONOSCOPY
The main complications of colonoscopy are perforation, bleeding, infection and
hypotension.
Perforation
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
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.
Infection
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.
Hypotension
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.
CONCLUSION
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.
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