notes by dr Claudio Italiano
The most important therapeutic aspect of colonoscopy is the removal of small colic polyps; is one of the greatest achievements in the field of gastroenterology. It has been shown that the removal of adenomas is able to consistently reduce the incidence of colon cancer. The polyps, both pedunculated and sessile, can be removed by endoscopy from any part of the colon. It is clear that the endoscopist will always request the histological investigation of the excised polyp and that in case of suspected cancer injury, he will always entrust the oncologist surgeon with the specific treatment of the case.
Many polyps are adenomas; this histology is typical of most small colon polyps (<5 mm). Since many polyps are adenomas, any polyps detected during a diagnostic colonoscopy must be removed at the same time. Every endoscopist must be able to perform a polypectomy when he or she identifies a polyp, which will happen frequently. It is not necessary for the patient to return for a subsequent polypectomy and there are no indications for an exclusively diagnostic colonoscopy.
The colon must be adequately cleansed in order to obtain a good visualization and to reduce the concentration of potentially explosive gas up to
non-combustible levels. This means that fermentable sugars (mannitol) should be
avoided when practicing the colon toilet from bacteria and faecal material. Any
other method of preparation is suitable for electrosurgery, be it beacon oil
associated with enemas, magnesium citrate with enemas, phosphosoda or
electrolyte solutions. Insufflation of the colon with carbon dioxide, which some
consider necessary to avoid the risk of explosions induced by sparks, is
considered optional. Before an endoscopic polypectomy it is not necessary to
check the coagulation parameters routinely. Many patients do not need to undergo
tests such as platelet counts, prothrombin time, bleeding time or coagulation
time.
On the other hand, it is important to look for a positive history of haemostasis disorders, including any tendency to excessive bleeding as a result of wounds, surgical procedures or dental extractions. Non-steroidal anti-inflammatory drugs and aspirin, which have specific anti-platelet properties, should be discontinued for one week prior to endoscopy. This precaution also applies to any over-the-counter medicine containing aspirin. Patients on anticoagulant therapy can undergo colonoscopy safely, but polypectomy should be avoided due to the risk of bleeding. When it is necessary to remove polyps in patients on high-risk anticoagulant therapy for thrombotic episodes (eg prosthetic heart valve carriers), a period of hospitalization is required, during which the anticoagulant effect will be maintained by means of heparin, which a short duration of action.
The coumadin must be interrupted. When prothrombin levels return to the normal range, polypectomy may be performed after discontinuing heparin therapy for four hours. If no bleeding occurs during the polypectomy, four hours later heparin may be re-administered and returned to coumadin therapy. The patient should remain in hospital under heparin treatment until the prothrombin time has returned to therapeutic levels.
All solid-state electrosurgical units are suitable. They are able to produce a
direct current (cutting current) or are characterized by interrupted waves (coagulation
current). Some devices are able to combine the two waveforms in order to obtain
a so-called "mixed current". When the electrosurgical unit is adjusted to the
optimal level, it will not be necessary to resort to an increase in power during
the removal of the polyp, whether small or large, or when alternating a
polypectomy loop with an insulated "hot" forceps. biopsy ". Several models of
polypectomy loop are available. A large loop measures approximately 6 cm in
length and 2 cm in width; a small loop measuring 3 cm in length by 1 cm in width.
Only a few endoscopists resort to the technique of making loops themselves;
mostly it is preferred to use those marketed by industries. There are no big
differences between the oval loops, shaped in crescent, or hexagonal, since the
technique is the same in all cases. A thin wire loop cuts an octopus more
rapidly than a thick wire, and this must be kept in mind when switching from one
type to another. The "hot biopsy" forceps is an electrically insulated clamp
that allows the current to flow through its entire length without dispersion at
the level of the colonoscope.
These clamps direct electrical energy into the
tissue surrounding the claws, simultaneously obtaining a cauterization of the
base of the polyp and the recovery of a bioptic fragment, enclosed in the
branches. In case of bleeding it is useful to have an appropriate equipment for
haemostasis. A needle of the type used for varicose veins is useful, since it
can be used for the injection of a 1: 10,000 adrenaline solution. The
availability of a thermal probe or a BICAP electrode is equally useful when
bleeding occurs.
The section of an octopus with the diathermic loop is the result of two forces. Both
must be used simultaneously to obtain a clean polypectomy, free from bleeding
and without excessive thermal damage to the colic wall. These two forces are the
heat, resulting from the cauterization, and the mechanical strength of the
section exerted by the closing of the loop of the loop. The heat alone is not
able to section a polyp, while the mechanical force alone can dissect the polyp,
but this would cause immediate bleeding by failing to coagulate heat on the
blood vessels. Both the cutting current and coagulation current (or a mixture of
both) can cause tissue heating, but the section of an octopus with only the
cutting current, which causes the burst of individual cells, can cause a
subsequent bleeding from the seat of polypectomy due to lack of adequate
haemostasis. A recent article (10) pointed out that the use of the mixed current
causes a higher incidence of immediate bleeding, while the use of pure
coagulation current is associated with a higher rate of delayed post-polypectomy
bleeding. The potency of the electrosurgical unit is variable. Each endoscopist
must determine the type of current to be used, the suitable power and the time
necessary to cut off a polyp. There are no rules regarding the number of W-s or
J to be used for the large or thin section of the polyp to the colonic wall.
In general, the power delivered should be medium or low and the current should be
pure or mixed coagulation. The release of energy should be continuous once the
polypectomy has been started (unlike what is done when the foot switch is
pressed intermittently), and the collaborator holding the loop should make the
maneuver slowly and not tighten the loop quickly; he must start closing the loop
when requested, after the beginning of the supply of the current. Much of the
section effect on the polyp is obtained by the mechanical force generated by the
withdrawal of the loop wire inside its sheath. The correct use of the
electrosurgical unit will provide the thermal coagulation of the vessels
sectioned inside the base of the polyp. Instead, the fabric will be discontinued
by the mechanical force of the loop closure.