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Epiglottoscopy and Epiglottis Camouflage
From insertion of the blade until visualization of the larynx there is a predictable, sequential exposure of landmarks that results from progressive advancement of a line of sight. As a laryngoscope blade is advanced over and down the lingual surface of the tongue, into the pharynx and then the hypopharynx, the line of sight moves from the uvula, to the posterior pharynx, and then, at the base of the tongue, the epiglottis.
With the curved blade the epiglottis is indirectly elevated, while with the straight blade the epiglottis is directly lifted. Once the epiglottis is visualized the operator knows where the larynx will be located. Effective epiglottis control (either indirectly with a curved blade, or directly with a straight blade) will then permit progressive exposure of laryngeal landmarks. The epiglottis is the great “secret” to laryngoscopy.
Novice intubators move right past the epiglottis, insert the blade tip too deeply, and then cannot recognize any laryngeal structures. They typically try to transfer their practice experience from an intubation trainer to an actual patient and find recognition of structures very difficult. This occurs because of unrecognized visual restrictions, epiglottis camouflage, and they have little understanding of detailed laryngeal anatomy. They also do not appreciate how fine positioning of the blade tip affects laryngeal exposure. They resort to extra lifting effort instead of having a gentle touch and a planned approach of progressive visualization of landmarks. Their response to a poor laryngeal view is to move the blade in and out with large movements, leading to edema, tissue trauma, bleeding, and possibly perforation of the upper esophagus or hypopharynx. The best way to avoid landmark confusion is to be obsessive about epiglottoscopy.
The mucosal appearance of the epiglottis is identical to that of the posterior pharyngeal wall. In a supine position, with poor muscular tone, or after the administration of muscle relaxants, the jaw and base of tongue fall backward and the epiglottis lies against the posterior pharynx. Depending upon head and neck position, and the manner in which the laryngoscope is directed, it is easy to advance over the epiglottis, which may be camouflaged against the pharynx. Over extension of the head, at the atlanto-occiptal joint, moves the base of the tongue and epiglottis backward and worsens this situation, as does secretions, blood, and vomitus.
To overcome epiglottis camouflage and make the epiglottis edge distinctly visible it is necessary to distract the jaw effectively and lift the base of the tongue. Keeping the face plane horizontal, and ideally elevating the head to ear-to-sternal notch position (or sometimes higher), permits optimal jaw distraction. A suction tip should be used to remove any fluids as the blade is incrementally advanced down the tongue and until the epiglottis edge comes into view.
Read more about epiglottoscopy and epiglottis camouflage
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Tongue control
The large, reverse Z-shaped flange of a curved blade allows tongue sweeping, and many operators have been taught to insert the blade with the handle tilted sideways, toward the right, and then insert the blade into the mouth at an extreme right lateral position. A potential problem with this approach is that the epiglottis and the larynx are then approached off angle. Depending upon the depth of insertion, this can create landmark confusion. The aryepiglottioc fold can be misinterpreted as the epiglottis edge, and if inserted too deeply the tip of the blade will pass under the posterior cartilages and nothing will be recognizable.
With the patient’s face plane parallel to the ceiling, the Dr. Levitan advises to follow the curve of the blade down the curve of tongue, slightly to the right of midline, until the epiglottis edge comes into view. In this first stage of laryngoscopy only a gentle force is required to distract the jaw downward, lifting the epiglottis edge off the posterior pharynx. The direction of the handle upon insertion and with initial jaw distraction is toward the patient’s feet, and at a very shallow angle as the blade is advanced down the tongue (perhaps only ~20 degrees up from horizontal). After the epiglottis has been recognized, and before the blade is engaged with greater force, the operator should check tongue position and move the blade rightward as necessary to effectively control the tongue. In practice, epiglottoscopy and tongue control
Bimanual laryngoscopy
If the tip of the curved blade is not fully seated into the vallecula no amount of lifting force will correctly elevate the epiglottis. The most efficient, quickest, and easiest way to sit the blade tip correctly is by applying bimanual laryngoscopy. The operator uses their free right hand to reach around to the anterior neck of the patient and apply external manipulation to the neck, specifically at the thyroid cartilage. This is a downward (backward, posterior) force on the neck.
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The tip of the blade is like a key being inserted into the lock of the vallecula. Bimanual laryngoscopy serves to fully insert the key all the way into the lock, and then allows turning the lock (elevating the epiglottis) and “opening” the larynx. In some cases bimanual larynoscopy may be best at the cricoid cartilage, or even the hyoid, although Benumof found that optimal manipulation was at the thyroid in almost 90% of cases. The operator need not be concerned about the exact position of their right hand. There is instantaneous visual feedback about the effectiveness of epiglottis elevation, and it is easy to move the right hand slightly up or down on the patient’s neck to optimize the view.
“External laryngeal manipulation” is synonymous with “bimanual laryngoscopy.” The later term is a better description of the technique because it provides much more information, and emphasizes the most critical aspect of the technique—namely, that the operator is connecting the actions of their hand with their view of the larynx.
Benumof JL, Cooper SD.Quantitative improvement in laryngoscopic view by optimal external laryngeal manipulation. J Clin Anesth. 1996; 8: 136-40.
Levitan RM, Kinkle WC, Levin WJ, Everett WW. Laryngeal view during laryngoscopy: a randomized trial comparing cricoid pressure, backward-upward-rightward pressure, and bimanual laryngoscopy. Ann Emerg Med. 2006; 47: 548-55.
Read more about Bimanual Laryngoscopy
Head Elevation
If the epiglottis has been visualized, and bimanual laryngoscopy performed, but an epiglottis-only view still persists, dynamic lifting of the head (i.e., head elevation) may significantly improve laryngeal exposure. This intubation and laryngeal exposure technique was well known to the early pioneers of laryngoscopy, and it has been validated through Airway Cam imaging, endoscopy, and numerous clinical studies in both cadavers and live patients. Head elevation permits greater jaw distraction because of its mechanically favorable effect on mouth opening. It also enlarges the area beneath the base of the tongue and epiglottis and thereby improving visualization. It is contra-indicated in cervical spine precautions.
Schmitt has shown in a large series of 1500 patients, in whom 21 were epiglottis-only views, that combining external pressure on the larynx with maximal head elevation provided a view of the larynx in 19 of the 21 difficult airways:
Schmitt HJ, Mang H., Head and neck elevation beyond the sniffing position improves laryngeal view in cases of difficult direct laryngoscopy.
Read more about Head Elevation
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Tube delivery is a separate piece of the intubation puzzle. Clinicians managing emergency airways need to appreciate how stylet shape, and the designs of the tracheal tube itself, impact on delivery toward the target and into the trachea. A properly shaped, styletted tracheal tube should have a narrow long-axis dimension permitting easy maneuverability. An upturned distal tip allows the intubator to watch the tube tip pass into the larynx. All instruments designed for placement in narrow body cavities have a narrow long-axis.
The proper shape of a styletted tube is straight-to-cuff with a 35 degree bend angle at the proximal cuff. Bend angles greater than 35 degrees will have mechanical problems passing into the trachea as the leading edge of the tube hits the anterior tracheal rings.
Straight-to-cuff stylet shaping aids maneuverability, but it also has an optical advantage in that the operator can keep their eye on the target, advancing the tube from below the line of sight, into the larynx. The upturned distal tip is used to pass above the interarytenoid notch and into the larynx, without ever obscuring the view of the larynx. Improper stylet shaping, i.e., using an arcuate shaped tube, is a common cause of esophageal and failed intubation despite adequate laryngoscopy.
Read more about stylet shaping and the optics of tube placement
Read more about the mechanics of tube insertion into the trachea
A tube introducer, a.k.a. a bougie, is a useful aid to intubation when faced with poor laryngeal exposure despite a best-practice approach to laryngoscopy. Because of its smaller outer diameter compared to a tracheal tube (5.0 mm vs. > 8.5mm for most adult sized tubes) some operators find it easier to insert without obscuring the target. The bougie combines this smaller outer diameter with an upturned distal tip (bend angle 38 degrees), and a narrow long axis. If a stylet is shaped in similar fashion, the bougie has little optical advantage over a straight-to-cuff styletted tube, and adds a step.
The bougie does provide tactile feedback as the rounded tip bounces over the anterior tracheal rings. For this reason, some advocate using the bougie in the epiglottis-only view. The problem is that the bougie cannot lift the epiglottis. It must be guided underneath it, and kept midline. Although it has some shape memory, getting it to pass anteriorly into the trachea, especially when the epiglottis is lying against the posterior pharyngeal wall (a Cormack-Lehane Grade 3b view) is very difficult.
The bougie advances into the trachea and will stop between 24 and 40 cm as it reaches the distal bronchi. The tracheal tube should be slid off the bougie using a counter-clockwise rotation; this closes the gap between the tube and bougie (outer diameter 2-3 millimeters smaller than the tracheal tube) that would otherwise catch at the laryngeal inlet (approximate tube depth of 14-16 cm at the teeth).
Read more about the bougie here
An optical stylet is a very useful laryngoscopy adjunct, although using a fiberoptic instrument represents a whole new skill set for many operators. It has the rigidity to lift the epiglottis, and provides visualization of the larynx when a direct line of sight is impossible. While it does have some limitations, especially in heavily soiled airways, the combination of a laryngoscope as a tongue retractor with a fiberoptic instrument on the first intubation attempt can be a very effective method of ensuring first-pass success, especially in high risk clinical situations.
Read more about optical stylets as a laryngoscopy adjunct
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Straight blade laryngoscopy for most patients is reserved for when the epiglottis can be identified, but not elevated. It is the primary laryngoscopy technique for infants and small children, and may be the first choice in some adults with a very short thyromental distance (receeding chin, i.e., a small displacement space), or those who have significant upper dental gaps (missing central incisors). It is generally harder to find the epiglottis with the smaller flange of a straight blade and tube delivery can also be more challenging.
Effective control of the tongue is critical for straight blade use, and important as well with curved blades. Any amount of tongue positioned to the right of a narrow lumen straight blade will make target visualization and tube delivery very difficult. The small flange height, especially of some Miller designs, prevents any kind of sweeping the tongue, and practitioners should not attempt to do so. Proper position is achieved with straight blades by deliberately directing the blade to the right paraglossal space. When correctly positioned the proximal portion of the blade is lateral to the right of the patient’s right nostril and no tongue is present to the right of the blade. The proximal blade should never be brought backward onto the central incisors; it should never be inserted into this area in the first place (where insertion will be restricted) but to the right of the right nostril as noted.
Tube delivery with a straight blade is from the extreme right corner of the mouth.
Read more about straight blade laryngoscopy
Laryngoscopy Algiorithm for First Pass Success
Epiglottoscopy and Dealing with Epiglottis Camouflage
Maximizing laryngeal exposure: Tongue control, bimanual laryngoscopy, head elevation
Passing the tube >> straight-to-cuff shape, <35º angle, bougie or optical stylet
Paraglossal Straight Blade Laryngoscopy
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