Practical Gastrointestinal Endoscopy

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CHAPTER 6
70–80% success in performing total colonoscopy, presumably
because some examinations were intolerable. If some degree
of ‘conscious sedation’ is used (typically equivalent in effect to
2–3 glasses of wine or beer), the patient is more likely to find the
examination tolerable, even enjoyable, or to have amnesia for it.
The endoscopist can perhaps be more thorough in the knowledge
that the patient is comfortable, and is also more likely to achieve
total colonoscopy in a shorter time. However, with heavy sedation
endoscopists can get away with ham-handed forcibly looping
technique—a bad investment in the long term, less likely to
achieve complete examinations, more likely to result in complications
and more expensive in instrument repair bills. It is often
said that it is dangerous to sedate, because the safety factor of
pain is removed; this is not strictly true, providing that the endoscopist
raises his own threshold of awareness as the patient’s
pain threshold is raised, responding to restlessness or changes of
facial expression as a warning that tissues and attachments are
being overstretched.
Most endoscopists use a balanced approach to sedation that
will be affected by many factors, including personal experience
and the individual patient’s attitude. A relaxed patient with a
short colon having a limited examination rarely needs sedation,
but an anxious patient with a tortuous colon, severe diverticular
disease, or a bad previous experience needs some protection. A
very few patients have such a morbid fear of colonoscopy, such
a low pain threshold or a known ‘difficult’ colon that it is justified
to resort to light general anesthesia. General anesthesia is
only likely to be hazardous when employed by an inexperienced
colonoscopist, able to use brutal technique because the anesthetized
patient cannot protest. However, even experienced
endoscopists are more likely to ‘push the limits’ and tend to
become more mechanistic when the patient is anesthetized and
‘out of it’.
Nitrous oxide inhalation
Fig. 6.1–Nitrous oxide/oxygen
mixture is breathed through a
mouthpiece.
Nitrous oxide/oxygen inhalation can be a useful ‘half-way house’
between no sedation and conventional intravenous sedation.
The 50·:·50 nitrous oxide/oxygen mixture is self-administered by
the patient, inhaling from a small cylinder fitted with a demand
valve. Breathing the gas through a small single-use mouthpiece
(Fig. 6.1) avoids the difficulties that can be experienced in getting
a good fit with a face mask, and also the phobia that some
patients feel for masks. Because of the possible teratogenicity of
passively inhaled nitrous oxide to females of child-bearing age,
a gas-scavenging system must be in place before routine use, but
may be unnecessary for occasional usage.
The patient is shown how to inhale, then ‘prebreathes’ for a
minute or so as the endoscopist prepares to start the procedure,