Practical Gastrointestinal Endoscopy

COLONOSCOPY AND FLEXIBLE SIGMOIDOSCOPY 143
hold a looping sigmoid colon straight and allow easier passage
into the proximal colon. As well as its use for stiffening a looping
sigmoid colon, an overtube can be invaluable for exchanging
colonoscopes or removing multiple polypectomy specimens. The
overtube can only be inserted when the sigmoid colon has been
completely straightened and the tip of the instrument is in the
proximal descending colon or splenic flexure. Use of overtubes
has largely fallen out of fashion because of their cumbersome
nature and unpredictability. With the use of 3D imaging, allowing
uncontrollable sigmoid looping to be accurately assessed
and straightened, it is possible that overtubes will once again be
found to be an occasionally useful accessory.
The original extremely stiff (wire-reinforced) overtubes had
disadvantages that discouraged most endoscopists from using
them. The tube had to be on the instrument before starting (or the
endoscope completely withdrawn before putting it on), and insertion
was sometimes traumatic, with perforations reported. A
soft-plastic split overtube overcomes all of these disadvantages,
and prototype atraumatic versions made of frictionless and very
flexible plastic material (Gortex) have proved effective. The split
overtube is placed over the shaft of the colonoscope after this
has been straightened to 50·cm at the splenic flexure (Fig. 6.64a).
The overtube split is sealed with adhesive tape and lubricated
with jelly (Fig. 6.64b), then inserted (without fluoroscopy) as far
into or through the shortened sigmoid colon as proves easy and
comfortable for the patient (Fig. 6.64c).
Resistance to insertion of an overtube means risky impaction against
a fold, loop or flexure; discomfort means the same. Both are indications
that further insertion or use of force could be dangerous.
The handle of the overtube is held by the assistant and the shaft
of the colonoscope pushed in through it (Fig. 6.65). As soon as
the colonoscope has been passed in satisfactorily (or at once if
the overtube cannot be inserted successfully) it takes only a few
seconds to remove the split overtube again, strip off the tape and
return to normal handling of the instrument.
The ‘reversed’ splenic flexure
Atypical passage around the splenic flexure occurs in about 1
patient in 20, if imaging is available to see what is happening.
The instrument tip passes laterally rather than medially around
the splenic flexure, because the descending colon has moved
centrally on a mesocolon (Fig. 6.66) (see p. 109). This is of more
than academic interest because, having passed laterally round
the flexure and displaced the descending colon medially, the
advancing instrument forces the transverse colon down into a
deep loop. The instrument is then mechanically under stress
and difficult to steer, and the hepatic flexure is approached from
below at a disadvantageous angle, making it difficult to reach the
Fig. 6.64–(a) Insert the split
overtube onto the colonoscope
shaft … (b)… seal the slit with
sticky tape and lubricate …
(c)… and slide the overtube in;
keep the endoscope stationary
with the other hand.
(a)
(b)
(c)