Time it Takes to Successfully Intubate the Patient With the GlideScope Clinical Trial
Some surgical procedures require general anesthesia (i.e., the patient is 'asleep'). When
under general anesthesia, these patients' airways must be managed to ensure continuous flow
of oxygen to the lungs, and in most cases, delivery of anesthetic gases to the lungs. Most
often for airway management under general anesthesia, a plastic breathing tube is placed
though the voicebox ("larynx") into the windpipe ("trachea"), a process known as "tracheal
intubation". To safely intubate, the larynx must first be exposed. In many cases, this is
achieved by using a device known as a direct laryngoscope, which is like a curved, lighted
tongue depressor. It is used to gently move the tongue out of the way, to expose the larynx.
When the larynx is easily seen, passing the breathing tube is usually also easy.
Unfortunately, in 2-5% of cases, it is difficult or impossible to view the larynx using the
direct laryngoscope. This then creates difficulty with tube passage. A number of options
exist to deal with this situation, including, within the last 10 years, a class of device
called "video laryngoscopes". These devices use a small video chip located towards the end
of the blade, which, by providing transmission of an image of the larynx 'around the corner'
to a screen outside the patient, enable a view to be obtained (when no such view could be
obtained with direct laryngoscope). With the larynx now indirectly visualized, tube passage
can proceed. However, it's not that easy. When using these 'around the corner'
videolaryngoscopes, tube passage can be more difficult, as the tube must be guided around a
90 degree bend from the mouth to the trachea, which sits at right angles to the mouth. Less
difficulty occurs with tube passage when the direct laryngoscope is used because the blade
compresses the tongue out of the way, creating a straight line from teeth to the larynx and
windpipe beyond.
The GlideScope is one example of video laryngoscope, and has been in use here at CDHA for 10
years. It has been extensively studied over the ten years, with more than 300 studies
appearing in the literature. The investigators know from these studies that it is very
effective at delivering a view of the larynx when direct laryngoscopy has failed to do so.
However, getting the tube to and through the larynx into the trachea, even with a good view,
can be problematic. Furthermore, it is the impression of some clinicians that when a
close-up, full view of the larynx is obtained (as is optimal for direct laryngoscopy) with
the GlideScope, tube passage appears to be a little more difficult than seems to be the case
when only a partial view of the larynx is obtained, from a little further away. The
investigators don't know why this may be so, but may relate to one or more of a number of
reasons, including (when too close) angling the larynx into an unfavorable angle, or (when
further away) more favorably reducing the angle between mouth and larynx and trachea.
However, no guidance on this question appears in the peer-reviewed medical literature, and
no studies have been done. There is some suggestion in non peer-reviewed internet sites on
airway management that a partial view may be better, but again, this has not been
scientifically studied or validated one way or another.
As mentioned, the GlideScope has been in regular use in CDHA for many years. Most often, it
is used when difficulty with tracheal intubation is anticipated or has already been
encountered in the anesthetized patient, although some airway experts suggest that within
the near future, all intubations will occur with some sort of video laryngoscope.
It is important to research the present question as in contemporary practice many
anesthesiologists, faced with a patient in whom they are anticipating difficult direct
laryngoscopy proceed with putting the patient to sleep, relying on the video laryngoscope to
enable them to intubate. With a patient now anesthetized and not breathing, if they then
have trouble intubating the patient in spite of getting a view of the larynx, harm could
occur to the patient from a failed intubation situation. Furthermore, there are now a number
of studies documenting that patient morbidity can increase with multiple intubation
attempts.
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