Basic principle of a videolaryngoscope (VL)
By using video laryngoscopes the practitioner views the larynx indirectly, allowing for an 'around-the-corner' view. As no direct line of sight between the practitioner's eye and the larynx has to be achieved, these devices have a role in situations where conventional laryngoscopy is difficult, particularly when the larynx is located anteriorly.
Diagram of laryngoscopy with a 'classic' MacIntosh blade. The goal of laryngoscopy with this kind of blade is to establish a direct line-of-sight between the practitioner's eye and the larynx, i.e. vocal chords.
Diagram of laryngoscopy with a videolaryngoscope blade. The viewpoint of the larynx is from the blade of the laryngoscope.
The shifting of the 'point of view' from the anesthesiologist's eye to the laryngoscope blade allows blade designs to be used with VLs which would not work well for direct laryngoscopy, e.g. the 'D-blade' on the C-Mac® system or the standard Glidescope® blade.
Comparing the designs of the Glidescope® and MacIntosh blades
VL blades are commonly more 'bent' than conventional MacIntosh blades in order to obtain a view of a more anterior larynx which cannot be easily visualised with conventional laryngoscopy.
Types of videolaryngoscopes
Videolaryngoscopes are either of the un-channelled or channelled type:
- Un-channelled videolaryngoscopes
These devices can facilitate visualization of the larynx when it is not possible to do so with a conventional blade. To achieve actual intubation the ET tube has to be loaded onto a stylet, then navigated into the field of view of the videolaryngoscope, and finally advanced into the laryngeal inlet.
- Channelled videolaryngoscopes
These devices include a channel for the ET tube which is integrated into the blade of the laryngoscope. The basic idea of the channelled VL is that once an adequate view of the laryngeal inlet is obtained and the scope is positioned correctly, advancing the ET tube within the channel will inevitably direct the tube tip between the vocal chords without need for additional steering or navigation of the tube. This is meant to address a major shortcoming of the un-channelled scopes, which is that navigation of the ET tube tip through the vocal chords can potentially still be difficult despite a good videolaryngoscopy view (the reason why a stylet is commonly required for intubation with an un-channelled videolaryngoscope).
An ever-increasing number of videolaryngoscopy systems are being marketed. While we only describe three systems here, this selection is not meant to indicate superiority of these devices!
Videolaryngoscopes are useful in a number of situations:
- Cases of anticipated difficult laryngoscopy or failed laryngoscopy
- To assist intubation with flexible fiberoptic scopes or optical stylets by creating a tissue passage in a narrow airway
- To document/ photograph upper airway and laryngeal anatomy, e.g. to assess recurrent laryngeal nerve and vocal chord function
- As a teaching tool
Some practitioners have advocated for the elective use of VLs in all intubations.