37.4.1 What Are the Implications of LTH for Anesthesiologists?
The presence of LTH has been associated with difficult airway management following the induction of anesthesia, and in most of the published reports, LTH seems to be either the only factor responsible for the difficulties with airway management, or the most important one. In many instances, the patients were asymptomatic, had a normal preoperative airway evaluation, and the difficulties were unanticipated. In the largest series published in the anesthesia literature, that of Ovassapian et al, none of the 33 patients reviewed retrospectively had an airway examination that suggested an increased potential for difficult laryngoscopy or intubation.11 However, unanticipated difficulties were experienced with either or both bag-mask-ventilation and direct laryngoscopy in all of them. The lungs of 12 patients were difficult to ventilate by bag and mask. In five cases, failed intubation occurred but there were no details as to the number of attempts at direct laryngoscopy; in one case two failed attempts were made; in nine cases three failed attempts were recorded; in 14 cases four failed attempts occurred; in three cases, there were five attempts; and in one case, six attempts were made before the procedure was abandoned. The tracheas of six patients were subsequently intubated using a fiberoptic bronchoscope (FOB) with the patient awake; four of these interventions were characterized as moderately difficult and two as easy. Of the remaining 27 patients who subsequently underwent FOB-assisted tracheal intubation, 4 interventions were deemed difficult, 12 were moderately difficult, and 11 were reported as easy. Difficulty was experienced passing the endotracheal tube over the FOB and into the trachea in 11 patients. All 33 patients were subsequently evaluated using fiberoptic pharyngoscopy to determine possible causes of the failure; the only finding common to all 33 patients was the presence of LTH.
Other authors have reported similar findings with either single cases or smaller series. But the themes are consistent with the report of Ovassapian et al; unanticipated difficulties were often encountered with ventilation of the lungs and intubation of the trachea.9,12,13 These difficulties with ventilation were not always or easily overcome with the use of laryngeal mask airways nor were difficulties with tracheal intubation routinely or readily overcome with the use of adjuncts or alternatives to the direct laryngoscope. Difficulties seem common even in situations where difficulties were anticipated and experienced anesthesiologists deployed advanced alternatives for airway management. It is fortunately the case that, in many of the reports, it was possible for the anesthesiologist to maintain sufficient oxygenation through a variety of interventions to safely abandon further attempts at intubation and awaken the patient. However, Jones and Cohle reported a death due to failed airway management in a 24-year-old patient presenting with probable appendicitis.14 Following induction of anesthesia, bag-mask-ventilation was impossible and tracheal intubation failed despite repeated attempts with both a direct laryngoscope and a fiberoptic bronchoscope. A tracheotomy was performed but the patient never regained consciousness and died 8 hours postoperatively. At autopsy, a large lingual tonsil was discovered.
In the patient described in the case, moderate difficulties were experienced with bag-mask-ventilation although it was possible to maintain her oxygen saturation in a clinically acceptable range. However tracheal intubation was unsuccessful with both direct laryngoscopy and with a lighted stylet. Because of the difficulties with ventilation, a decision was made to attempt placement of a laryngeal mask airway, which was successful and resulted in an effective airway.
37.4.2 How Do Lingual Tonsils Interfere with Bag-Mask-Ventilation and Direct Laryngoscopy?
If the lingual tonsils are large enough, the airway is obstructed at the base of the tongue and elevation of the tongue may be inadequate to relieve the obstruction. Placement of an oral airway may result in the distal aperture of the airway being directly opposed by the tonsillar mass and obstructed as well. It is possible that a nasal airway may better bypass the obstruction caused by LTH than an oral airway, but this is by no means certain. In the patient described in the case, an oral airway did not seem to reduce the difficulties with bag-mask-ventilation and no attempt was made to place a nasal airway.
Successful laryngoscopy is dependent on the development of a line-of-sight from the eye to the larynx. Most difficulties with direct laryngoscopy can be grouped into a limited number of categories: mouth opening is inadequate to admit the blade adequately; airway angles are sharp and irreducible; soft tissues are either overabundant and compromising or noncompliant and unyielding; there are obstructing masses present; or blood and secretions interfere with light reflection. Horton et al demonstrated the importance during laryngoscopy of control of the hyoid bone with the tip of the laryngoscope blade reporting that the body of the hyoid was drawn forward and tilted downward.15 This tip placement resulted in tensioning of the hyoepiglottic ligament, elevation of the epiglottis, and exposure of the laryngeal structures. Tripathi and Pandey similarly reported that placement of the tip of a curved Macintosh blade in the pre-epiglottic space (vallecula) proximal to the hyoid bone achieved elevation and tilting of the hyoid bone, tensioning of the hyoepiglottic ligaments, and an optimal glottic view.16 The presence of the LTH at the base of the tongue, in the pre-epiglottic space, will prevent proper placement of the laryngoscope blade thus interfering with the basic mechanisms of laryngoscopy. The obstruction of the airway lumen by the LTH is the second factor that will interfere with the direct laryngoscopy.
The presence of the lingual tonsil may completely obstruct the line-of-sight necessary for successful laryngoscopy. Many of the alternatives to the direct laryngoscope, such as the indirect fiberoptic and video-optic laryngoscopes, also depend on the development of a line-of-sight from the instrument tip and this requirement may render them ineffective for the task of airway salvage if direct laryngoscopy proves to be impossible due to LTH. The use of blind techniques, such as the lightwand, in the presence of a known soft tissue mass in the airway is controversial and some would consider such techniques to be contraindicated due to the risk of tissue trauma and bleeding.
37.4.3 What Airway Management Practices Have Been Employed in Patients with LTH?
In the majority of reports, airway management difficulties were unanticipated and included both difficult or failed ventilation and intubation. The use of laryngeal mask airways is a common feature in the reports; the outcomes of LMA deployments ranged across the spectrum from successful ventilation and intubation using the LMA as a conduit for tracheal intubation, to no improvement in ventilation and continued failed intubation. With respect to difficulties encountered with intubation, in those scenarios that were unanticipated, the most common response was persistent attempt at direct laryngoscopy without success. The use of flexible bronchoscopes, Eschmann tracheal introducers (bougies) and intubation catheters, straight blades, and an anterior commissure blade by an otolaryngologist have all been reported with variable results.
The most common technology reported as being deployed in anticipated difficult situations (interventions made subsequent to the diagnosis of LTH being made) has been the flexible bronchoscope (FB), typically in an awake patient. Although usually successful, difficulties with both accessing the airway with the FB and subsequently with advancing the endotracheal tube into the trachea are common. These difficulties likely result not only from the obstruction of the airway lumen by the LTH but also from the requirement to pass deep to the LTH with the FB along the posterior pharyngeal wall, then to turn sharply in the opposite direction to access the laryngeal inlet, and finally to turn one more time to pass into the tracheal lumen. The turning radius of the FB is likely an issue when multiple turns have to be executed over a short distance.
The Bullard laryngoscope was employed in this case as it was thought that it would be capable of lifting the epiglottis and the tonsil to allow access to the laryngeal inlet. By performing the laryngoscopy in an awake patient, it was presumed that if a laryngeal view could not be obtained, the procedure could be safely abandoned and an alternative technique attempted.
37.4.4 What Is the Role of Extraglottic Airways in the Management of LTH?
The most commonly deployed extraglottic airway reportedly being used has been the laryngeal mask airway (LMA), in one form or another. These have been placed to facilitate both ventilation and intubation with varying results. In some reports, difficult ventilation was improved after the placement of the LMA, but intubation through the device was not possible.9,13,17 In other reports, placement of an LMA resulted in both a resolution of difficult ventilation and provided a conduit for successful tracheal intubation.2,18 Finally, some authors report little apparent improvement in difficult ventilation after placement of an LMA and failed attempts at intubation using the LMA as a conduit.12,19 The success of the LMA in reducing the severity of difficult ventilation and providing an intubation conduit in the setting of LTH is likely impacted both by the size of the tonsil, the position of the LMA orifice in relation to the laryngeal inlet, and the degree of airway obstruction resulting from the tonsillar hypertrophy. In most reports, placement of an LMA has resulted in some reduction in the ventilation difficulties being encountered. The available reports support a recommendation that placement of an LMA be considered early if difficulty with ventilation is being experienced in the setting of an LTH. Whether a smaller than usual LMA may provide equal or greater benefit in this setting is speculative.
A laryngeal mask airway was placed easily in the case described and resulted in a much improved airway. A size 3 LMA was used, although it would have been conventional local practice to use a size 4 in this patient.
37.4.5 Which of the Available Airway Technologies Should Be Most Effective in the Setting of LTH?
There are two anatomic issues relevant to airway management which must be considered in a patient with LTH. The first issue is the angles to be negotiated between the mouth and the glottic inlet and the second is the degree of obstruction of the airway lumen by the tonsil. As discussed, if the tonsils are very large, then to either access the laryngeal inlet or obtain a view of the larynx, the airway instrument must pass deep to the base of the tongue and behind the tonsil along the posterior pharyngeal wall. To get a view of the larynx, it must then move sharply anteriorly and away from the posterior pharyngeal wall to develop the line-of-sight. To access the laryngeal inlet it also must pass anteriorly and over the posterior commissure, and then turn once again to move down through the cords, and into the tracheal lumen. If the instrument is dependent for its success on the development of a line-of-sight from its tip to the laryngeal inlet from a point in the airway above the larynx, this line-of-sight is likely to be obstructed by the presence of large tonsils.
A rigid device such as the Bullard™ laryngoscope (BL) is possibly the ideal instrument for the management of the airway in a patient with LTH, both in the anticipated and unanticipated scenario.18,20 It is capable of negotiating the angles described and its robust construction permits gentle manipulation of airway tissues, allowing it to create the necessary endoscopic airspace. It may be used to gently elevate the lingual tonsil to reduce the degree of obstruction and, when placed in its final position, the tip of the BL rests beyond the lingual tonsil in the laryngeal inlet, bypassing the lumenal obstruction caused by the tonsil. Although the BL does require a line-of-sight from blade tip to target, typically the blade tip should be placed beyond the tonsil when positioned. Because it can carry the tracheal tube mounted on its dedicated stylet, no second working channel is needed for tube placement—an obvious advantage in the patient with a lingual tonsil and a relatively noncompliant airway. As well, in the scenario of an airway mass, the BL can be fitted with a standard surgical camera, allowing for visualization of the entire intervention and reducing the potential for trauma to the tonsil. Despite the theoretic advantages of an instrument, such as the BL for the management of the airway in a patient with LTH, it would be imprudent to conclude that it would always be effective.
The FB may also be used to successfully negotiate the angles described and is also capable of bypassing the obstructed lumen. Whereas a rigid instrument may be used to elevate tissues and reduce the angles which must be negotiated, the FB must negotiate them as it finds them. It may be very difficult to traverse the airway due to the repeated turns which must be executed over a relatively short distance. As well, it may be difficult to avoid soiling the bronchoscope on the tonsil or cause bleeding by contacting the tonsil if there is a high degree of obstruction of the lumen. Finally, passing the tube over the FB may prove difficult as well as the tube must negotiate the same angles previously negotiated by the FB. Warming the endotracheal tube and the use of a Parker-type tube and ensuring a close match between tube and FB diameters may all increase the likelihood of successful tube passage. As well, combining a rigid blade with the FB and using the blade to elevate the soft tissues to permit passage of the FB may be an effective salvage strategy.
Ultimately, it may not be possible to secure the airway from a supraglottic approach and either a retrograde or an infraglottic surgical approach may be necessary. A wire inserted through a cricothyroid membrane puncture could be used to facilitate either a retrograde intubation or to guide a supraglottic technique (eg, threading an FB loaded with an endotracheal tube). Cricothyrotomy or tracheotomy may be performed either electively or urgently if a "cannot intubate-cannot ventilate" situation is encountered.
As previously noted, and for the reasons already outlined, awake tracheal intubation was attempted with a Bullard™ laryngoscope. The Bullard™ blade was placed under the epiglottis and used to gently elevate both the epiglottis and the tonsil affording a full view of the larynx. Intubation of the trachea was readily achieved using a tube mounted on the dedicated stylet.
37.4.6 How Should the Algorithms of Chapter 2 Be Applied to the Care of the Patient with LTH?
If LTH is recognized before the induction of anesthesia, the airway assessment would be considered non-reassuring and concerns would be raised regarding both bag-mask-ventilation and tracheal intubation. Given that assessment, management would be directed by Panel A of the ASA Difficult Airway Management Algorithm in Figures 2-1 and 2-2, or the Emergency Difficult Airway Algorithm in Figure 2-5 and an awake intubation would be recommended; consideration should also be given to a surgical airway in some instances. If LTH was unanticipated and difficulties are experienced with ventilation and/or intubation, management would be directed by Panel B of the ASA Difficult Airway Management Algorithm in Figures 2-1 and 2-2 or the Failed Airway Algorithm in Figure 2-6.
37.4.7 What Is Optimal Elective Airway Management in a Patient Known to Have LTH?
Although bag-mask-ventilation has usually been possible in situations where LTH was unanticipated and encountered, both difficult and failed ventilation have been reported. As well, difficult and failed intubation using either direct laryngoscopy, and adjuncts and alternatives to the direct laryngoscope are common. It is the author's opinion that the airway assessment in a patient known to have LTH is non-reassuring with respect to both bag-mask-ventilation and tracheal intubation and an awake intubation is both the most prudent and optimal approach to airway management as dictated by the ASA Difficult Airway Management Algorithm (Figure 2-2).