Practical Gastrointestinal Endoscopy

THERAPEUTIC COLONOSCOPY 177
units adjusts output automatically for appropriate heating during
snaring.
‘Slow cook’ is the essential principle of polypectomy, y so as to
electrocoagulate an adequate length of stalk tissue before section.
There should be visible whitening as the protein denatures,
with swelling or even steam as the stalk tissue boils. Remember
that some tissue necrosis effect may extend beyond the zone of
obvious electrocoagulation whitening, which is a particular consideration
in avoiding mucosal ulceration and secondary bleeds
after ‘hot biopsy’ in particular. However, if all the water boils
off, electrons will no longer flow through the desiccated tissue
of a polyp stalk and the wire may have to be pulled through mechanically—in
principle a somewhat risky thing to do, because
thick-walled vessels are usually the last part to sever. Inevitably
it takes a little time at the safer lower current settings to heat
the tissue but, if this takes more than 30– 40 seconds, the risk of
heat dissipation at a distance (anddamage to the bowel wall) increases
and it may be more realistic to increase the power setting
to speed things up. The maximum power setting used should be
equivalent to no more than 30 –50·W.
Thick stalks (1·cm or more in diameter) are more difficult to coagulate,
with a risk of inadequate central vascular electrocoagulation,
particularly if the stalk is firm and relatively non-compressible
and the vessels within it are large and thick-walled. A higher
power setting may be needed to start electrocoagulation peripherally
or tight snaring may be needed to start electrocoagulation,
with a rapid increase of heating and the unfortunate effect that,
as the snare starts to transect and close down through the stalk,
the heat produced increases very dramatically. This results in
electrocutting of the central core, precisely the part that needs
slow and controlled coagulation. Additional factors such as current
leakage from ‘contralateral’ contact points may complicate
things further and are discussed later.
If no coagulation is occurring in a large polyp stalk check:
•–Are the circuitry and connections correct?
•–Is the snare handle properly assembled and closed?
•–Has the stalk been correctly snared—or the head trapped out of sight
(see Fig. 7.3)?
•–If the stalk is very thick consider epinephrine injection (Fig. 7.19),
have nylon loop or clip ready.
•– Can the snare loop be repositioned higher up the stalk where it is
narrower?
If there is any fear of complications or the operator is inexperienced,
this may be the moment to disengage the snare andleave
the procedure to someone else (see below for how to disengage
a ‘stuck’ snare).
(a)
(b)
Fig. 7.18 When snaring a thick
stalk (a) the plastic sheath may
crumple before closure is adequate
(b).
(a)
(b)
1cm
Fig. 7.19 (a) Thick stalks can
bleed—think of pre-injection. (b)
The distance to theclosure mark
indicates thestalk size.