5. Videolaryngoscopy Flashcards
Conventional direct laryngoscopy:
Direct laryngoscopy has been a core anaesthetic skill since
Janeway devised the precursor of modern laryngoscopes in 1913.
It remains the gold standard in as much as it may provide an uninterrupted view of
the laryngeal inlet, but it is nonetheless a technique of some complexity.
It requires the alignment of the oral, the pharyngeal and the tracheal planes
into a single visual axis from the incisors to the glottis;
and laryngoscopy and tracheal intubation will be
made more difficult by anything which impedes that process.
Such factors include limited
mouth opening,
prominent upper incisors,
a pronounced overbite,
macroglossia,
an arched palate,
an infantile epiglottis and
a high anterior larynx.
But even in a normal airway the attainment of a Cormack and Lehane Grade 1 view (in which
the whole glottis is visible) may require considerable physical manipulation, including
occipital extension, neck flexion, external laryngeal pressure and substantial
lifting forces imposed by the laryngoscope blade in the vallecula.
Videolaryngoscopy
This can mitigate some of these factors.
It is not necessary to obtain a direct visual axis,
and video laryngoscopes allow the glottis to be seen indirectly.
This can minimize potentially traumatic airway manipulation with less
movement of the head and cervical spine, and with much lower lifting forces.
Basic design
The various available devices have different features,
but in terms of the physical principles all simply use forms of
video camera technology to allow an indirect view of the glottis.
High-resolution digital cameras at the tip of the laryngoscope
blade can produce high-definition images, either on a small screen attached to
the device itself or on a larger monitor.
The proximity of the camera to the glottis provides a much wider angle of view than is typical when a 15’ direct laryngoscope is used.
Classification of videolaryngoscopes. This is evolving as newer models are
introduced; however, one accepted classification of these devices is into:
- Macintosh-modification.
- Tube/guide channel.
- Angulated blade.
Macintosh-modification.
An example of this design is the McGrath Mac,
which essentially integrates video technology with a conventional Macintosh laryngoscope.
This design means that the device can give an indirect view but can also be used to
obtain a direct view of the glottis in the traditional way.
(It can also be classified as an angulated blade device.)
Tube/guide channel
An example of this design is the Airtraq.
These devices have a guide channel with a preloaded tracheal tube.
The Airtraq has a small video screen attached to the handle but the
camera can be attached to a monitor as desired.
Angulated blade.
An example of this design is the GlideScope.
The angulated blade is designed to allow a video view of the glottis with minimal manipulation of the head and neck, although a greater tilt of the handle may be necessary with greater potential risk to the upper incisors.
The tracheal tube is preloaded with a curved stylet which takes it round the natural hypopharyngeal curve.
Once the tube is at the glottis the stylet is removed,
the tube straightens, and as it does so it advances
into the trachea automatically without the need for any further
downward movement of the tube.
Evidence of benefit:
the currently available videolaryngoscopes are different in design,
as are the groups of medical professionals in the studies which have reported
their use,
so there are as yet no unequivocal data to support their introduction into
routine practice.
The main outcome measures are successful intubation, first-time
intubation and time to tracheal intubation.
In a group of unselected patients, intubation using direct laryngoscopy will be straightforward in 95%, so it is no surprise that videolaryngoscopy is no better than direct laryngoscopy.
In patients in whom difficult intubation is suspected and in unexpected difficult laryngoscopy,
videolaryngoscopes increase the proportion of Cormack and Lehane Grade 1 views.
(Not all the devices are the same and so this is a generalization. It would be
unreasonable were an examiner to start asking about the specific differences say
between the Pentax AWS and the V-MAC models).
It is also the case that, although Cormack and Lehane grades correlate well with the ease or otherwise of intubation after direct laryngoscopy, that may not be so with videolaryngoscopy in which a good view of the glottis is not necessarily associated with success.
Many of the studies give no accurate assessment of the competence and experience of the operators, and this also limits the conclusions that can be drawn.
Hence, these conclusions are limited essentially to the fact that the devices can certainly improve the laryngeal view that is
obtained, especially with non-experts, and especially in cases with Cormack and
Lehane grades 3 and 4. Whether or not this translates to a higher success rate in
tracheal and in difficult tracheal intubation has yet to be established.
Despite the lack of uniformity in the studies, however, the overall impression given by the enthusiasts for the technique is that the videolaryngoscope is an easier device to master than the traditional laryngoscope, that it can provide a better view and that in due course it
may well become the default means by which the trachea is intubated.
Difficult Airway Society (DAS)
Guidelines 2015. Airway guidelines invariably involve quite detailed
algorithms which it is not practicable to reproduce during an oral.
You might, however, be asked to outline your approach to an unanticipated
difficult intubation.
The 2015 DAS guidelines are the most recent (at the time of writing), but it is possible that in due course the updates will have more emphasis on newer technologies.
Otherwise, in summary, the steps of the basic algorithm can be
described as follows.
(As always any algorithm should always be considered in
context. Unanticipated difficult intubation will require different management if it
occurs in a leaking aortic aneurysm or a category one caesarean section rather than
an elective laparoscopic cholecystectomy.)
- Attempted laryngoscopy and tracheal intubation
- Rescue via second-generation supraglottic airway device (SAD)
- Actions after successful SAD ventilation
- Actions after failed SAD ventilation
- Actions after failed facemask ventilation.
- Attempted laryngoscopy and tracheal intubation
On the assumption that the patient is in the optimal position for laryngoscopy,
that the appropriate blade is being
used and that neuromuscular paralysis is adequate,
the algorithm suggests manoeuvres such as external laryngeal pressure,
the removal of cricoid pressure in cases where it is being employed,
the use of a bougie and a maximum of three plus one attempts
(the last by a more experienced clinician if available).
These attempts can include the use of a videolaryngoscope.
Multiple failed attempts risk airway trauma
and the development of a ‘Can’t intubate, can’t oxygenate’ (CICO) scenario.
- Rescue via second-generation supraglottic airway device (SAD)
Should laryngoscopy fail,
the guidelines recommend the use of a second-generation
SAD such as a Pro-Seal or LMA Supreme.
(These airways include features such as oesophageal drainage tubes,
posterior inflatable cuffs and integral bite blocks.)
Again, three attempts with or without a change of device are recommended.
During these steps oxygenation and anaesthesia must be maintained throughout.
- Actions after successful SAD ventilation
. Should SAD insertion and ventilation
be successful, the options thereafter depend on the surgical context and the risk and
benefits of proceeding. Alternatives are (i) to proceed without intubation, (ii) attempt
to intubate via the SAD, (iii) continue to a surgical airway or (iv) allow the patient to
awaken.
- Actions after failed SAD ventilation.
Should SAD ventilation fail, then the anaesthetist should revert to facemask ventilation using a two-handed, two-person technique as necessary.
If oxygenation is maintained by this method then the patient should be allowed to awaken
- Actions after failed facemask ventilation.
This CICO scenario should be managed
by emergency front-of-neck access.
