Practical Gastrointestinal Endoscopy

THERAPEUTIC COLONOSCOPY 173
2–A smooth ‘feel’ is essential for safety; the snare handle and wire
should open and close easily so that the endoscopist (or assistant)
has an accurate idea of what is happening if the snare loop is
out of view behind the polyp or its stalk. A reusable snare inner
wire that has been bent in use or cleaning and no longer moves
freely within its plastic outer sheath is hazardous and should be
discarded.
3–Snare-wire thickness greatly affects the speed of electrocoagulation
and transection. Most loops are made of relatively thick
wire so that there is little risk of cheese-wiring unintentionally
and there is a larger contact area which favors good local coagulation
rather than electrocutting. Some single-use snares have
thin wire loops and need a lower current setting or care in closure
to avoid cutting too rapidly, before full coagulation of stalk
vessels. Be careful if using a new snare type.
4–Squeeze pressure is very important, especially when snaring
large polyps. There should be a 15·mm closure of the wire loop
into the snare outer tube before use (Fig. 7.4a). This ensures that the
loop will squeeze the stalk tightly even if the plastic outer sheath
crumples slightly under pressure, a particular problem with large
stalks (see p. 174). If squeeze pressure is inadequate (Fig. 7.4b) the
final cut may have to rely entirely on using high-power electrical
cutting and may not coagulate the central stalk vessels enough,
with potentially disastrous (bleeding) consequences. If the loop
closes too far (Fig. 7.4c) cheese-wiring can occur before electrocoagulation
is applied. This can also result in bleeding.
Yes
(a)
No
(b)
No
(c)
15mm
Fig. 7.4 (a) Snare closed 15·mm is
right; (b) wire too loose; (c) wire
too tight.
Other devices
Hot biopsy forceps are used to destroy small polyps up to 5·mm
in diameter and even for electrocoagulating telangiectases or
angiodysplasia, if argon plasma coagulation (APC) is unavailable
(see pp. 13–14, 183).
Polyp retrieval is possible with a variety of accessories—memory
metal Dormia-type basket, nylon net, multi-prong grasping
forceps and a polyp suction trap. These can all be useful, especially
for multiple or piecemeal-removed polyp specimens, but a
snare loop is often adequate for picking up a severed polyp and
saves time in changing accessories.
Injection needles are invaluable for saline or epinephrine
(adrenaline) injection, whether for elevation of sessile polyps, to
prevent or arrest bleeding or to tattoo a polypectomy site.
Dye-spray cannulas allow visualization or surface detail interpretation
of small or flat polyps, and the margins of sessile
polyps, althoughdye can (perhaps more easily) also be syringed
in without a cannula.
Clipping or nylon-loop placement devices have an occasional
invaluable place, either to deal with postpolypectomy bleeding
or to prevent it. The metal clips available are too short-jawed to