|This image can be seen in its original context here.|
Direct laryngoscopy requires the direct visualization of the laryngeal opening by the operator. For this to be achieved, the patient needs to be positioned in a way to allow the oral, pharyngeal, and laryngeal axes to align. The ability to manipulate the patients body and airway to achieve alignment of these three axes is what distinguishes an expert incubator from a less experienced one. Regardless of experience and expertise, this will not always be possible.
|A review of laryngeal anatomy can found on Dr. Richard Levitan's website airwaycam.com.|
|Figure 6 in Mace SE., 2008: Oral-pharyngeal-tracheal axes for intubation. (A) Nonaligned position. (B) Aligned sniffing position with neck flexed and head extended.|
Video laryngoscopy renders the need to achieve this alignment obsolete. All that has to be done to obtain visualization of the airway is insert the blade midline and pull back on the handle until the vocal cords come into view. Sweeping of the tongue and extension of the neck are not needed. While achieving a good view of the cords is relatively easy, passing the endotracheal tube can be challenging.
I have recently taken the "Difficult Airway Course, Anesthesia", and had the opportunity to discuss this shortcoming with some experts that have had a significant amount of experience with those video devices. Below is a list of some of the techniques and tips they had to offer.
1) Settle for a Cormack-Lehane grade 3 view:
Because of the ease by which a good view can be achieved with video laryngoscopy, it is often tempting to attempt to achieve the highest quality view when inserting the blade. However, in order to improve the view from a Cormack-Lehane 3 to a 2 or even 1, more pressure is put on the handle of the laryngoscope. This pressure is in turn transferred to the anterior aspect of the pharynx, pushing it further anterior and making the angle more acute and harder to reach with the endotracheal tube. As a result, settling for a Cormack-Lehane grade 3 view would avoid exacerbating the angle of the larynx and make it easier for the endotracheal tube to reach the cord opening.
2) Increase the curvature and the angle of the stylet:
Often times the laryngeal inlet cannot be seen by direct laryngoscopy because it is too anterior. While the exaggerated angle of the video laryngoscope will facilitate bringing the opening of the larynx into view, a "hockey stick" angled endotracheal tube may not be able to reach the airway. Even pre-formed stylets such as the one provided with the Glidescope® may not be angled enough in some circumstances. In those situation just use any available malleable stylet and angle it as pictured below.
|A) Classic "hockey stick" curve. B) Suggested curve for use with video laryngoscope.|
However, because of the tube's angulation with regard to the airway opening, you may need to partially withdraw the stylet in order for it to enter the airway. You can either ask an assistant to pull on the stylet slowly when you are in the proper position or, alternatively, bend the tip of the stylet that is protruding from the proximal aspect of the endotracheal tube towards you. This will allow you to use your thumb and retract it yourself.
This technique is similar to applying cricoid pressure in order to bring the vocal cords into view. The major difference lies in that the pressure is applied to the thyroid cartilage to decrease the angle of the larynx. The view can be further improved by simultaneously flexing the patient's head.
|Pressure on thyroid cartilage and neck flexion (black arrows) resulting in posterior displacement of the laryngeal inlet (green arrow). Drawing by Janet Fong©.|
Mace SE. Challenges and advances in intubation: airway evaluation and controversies with intubation. Emerg Med Clin North Am. 2008 Nov;26(4):977-1000, ix.