**2. Types of video laryngoscopes**

As previously stated, the GlideScope® was the first readily available video laryngoscope. Today, many variations of video laryngoscopes exist, each with its own advantages and disadvantages when compared to one another. Video laryngoscopes can be broken down by two categories: blade type and whether they are channeled. Two main types of blades exist: the Macintosh blade and the acute-angle blade. Macintosh blades maintain the traditional shape as used in direct laryngoscopy. Acute-angle blades, as the name suggests, are hyper-angulated to allow for better anterior visualization. Channeled scopes are shaped to match the anatomic curve of the upper airway and the built-in channel provides a guided passage for the endotracheal tube. The different blade types and presence of a channel offer different advantages and disadvantages.

Examples of available Macintosh-style blades include the GlideScope®, Storz C-MAC (single and reusable), and McGRATH™ (single use). An advantage of these blades is most providers are familiar with this style of blade in terms of its shape and technique for use. The blade is shaped with the same angle as a direct laryngoscope. The provider follows the same initial steps for airway management including patient positioning, mouth opening, rightward insertion of blade, sweeping of the tongue, and direct advancement past the soft palate. At this point, the provider can continue use of this blade for direct visualization or indirectly visualize the airway using the device-specific video source. The blade is either directly or indirectly guided into the vallecula, and the epiglottis is lifted to expose the vocal cords. The provider directly visualizes the endotracheal tube entering the mouth and advancement past the soft palate after which the provider again has the choice of either directly or indirectly viewing the advancement of the tube through the vocal cords. It is important to stress the direct visualization of both the blade and tube past the oral cavity and soft palate as an indirect technique will put the patient at high risk for injury. The options provided by this type of blade allow for greater flexibility in technique for the provider and improved teaching of techniques, with all present having the ability to see what the laryngoscopist views. The video source allows for a supervising provider to see in real time what the performing provider sees, allowing for instruction or assistance on both direct and indirect techniques. For more difficult airways, the ability for multiple clinicians to view the airway can allow for earlier assistance.

As for acute-angle video laryngoscopes, examples of available devices include GlideScope® LoPro, Storz C-mac D-blade, and single-use GlideScope® AVL and McGRATH™ X-blades. These blades are oriented upward at a steeper angle as previously mentioned, allowing for better anterior visualization. For example, the GlideScope® blades are oriented upward at a 60-degree angle. Due to this angulation, these blades cannot be used for direct visualization and require the use of a stylet or tracheal introducer. The technique again begins with proper patient positioning and opening of the mouth in the same fashion as with direct laryngoscopy. The blade however is inserted midline and the tongue is not displaced. The blade is directly visualized until passing the soft palate. At this point, indirect visualizing of the blade into position is required. It is typically unnecessary to advance the blade fully into the vallecula, as deep insertion will rotate the laryngeal axis anteriorly, increasing the difficulty of endotracheal tube insertion. A shallower insertion will allow for a wider visual field, provide a straighter pathway for endotracheal tube delivery, and decrease both the distance from lips to the camera and the area of blind-zone during which the provider cannot see the tube tip. One study demonstrated a deliberately restricted

### *Video-Assisted Laryngoscopy and Its Effects on Difficult Airway Management DOI: http://dx.doi.org/10.5772/intechopen.108176*

view resulted in faster and easier tracheal intubation with no additional complications [1]. Gently lifting the blade will allow for proper visualization after which the endotracheal tube can be indirectly advanced past the soft palate and then indirectly passed through the vocal cords and removing the stylet prior to full advancement into the trachea.

Channeled blades are shaped to match the anatomic curve of the upper airway and to be positioned around the base of the tongue. This allows for exposure of laryngeal structures while reducing cervical manipulation and not requiring tongue displacement. The endotracheal tube is advanced through the channel and hence a limitation is that it is not possible to independently manipulate the tube. The bulkier design and limited use in patients with small mouth openings are additional disadvantages. Examples of these blades include AIRTRAQ AVANT, Airway Scope (Pentax), and King Vision (Ambu). Typically, these blades are entirely disposable or have single-use components.
