Alternative Transoral Application of Nasopharyngeal Airways

Abstract

Transoral application of a nasopharyngeal airway (NPA) is a novel technique for difficult airway management. Clinically, it is an effective alternative for use in nonintubated dental cases under total intravenous anesthesia. This technique can help improve oxygenation and ventilation in clinical situations in which the conventional use of NPAs is ineffective, such as in patients who have findings of obesity; mandibular retrognathia or hypoplasia; maxillary hypoplasia; macroglossia; nasal obstruction secondary to hypertrophic tonsillar, adenoid, and/or lymphoid tissues or nasal polyps; known unusual nasal anatomy (eg, septal deviation); high risk of prolonged epistaxis (eg, patients on anticoagulants); or those who demonstrate mouth-breathing behaviors during deep sedation/nonintubated general anesthesia. After ensuring proper supraglottic placement, the transorally positioned NPA can be further secured with the use of tape for the duration of the dental procedure. Unlike an oropharyngeal airway, this simple and cost-efficient technique facilitates intraoral access for dental treatment.

Dental treatment for spontaneously ventilating patients using total intravenous anesthesia to provide deep sedation/nonintubated general anesthesia (DS/GA) often requires concurrent use of airway adjuncts to maintain airway patency. A nasopharyngeal airway (NPA) is often the preferred airway adjunct in nonintubated DS/GA dental cases because the Guedel oropharyngeal airway (OPA) or the flexible laryngeal mask airway may impede intraoral access. However, in patients who have findings of obesity; mandibular retrognathia or hypoplasia; maxillary hypoplasia; macroglossia; nasal obstruction related to tonsillar, adenoid, lymphoid tissue hypertrophy, or nasal polyps; known unusual nasal anatomy; high risk of prolonged epistaxis (eg, patients on anticoagulants); or who demonstrate mouth-breathing behaviors during DS/GA, the NPA is often ineffective or contraindicated because of its inherent application through the nares and passage through the nasal cavity and nasopharynx. To address this concern, ventilation and the delivery of supplemental oxygenation in these particular patients undergoing dental procedures can be greatly improved by the unconventional oral placement of an NPA (O-NPA) at the posterior oropharynx. This technique is described in this article.

METHODS

Placement of the O-NPA in the posterior oropharynx requires the patient to be deeply sedated or generally anesthetized to sufficiently blunt the cough, gag, and laryngeal reflexes. Ideally, the patient should be positioned in the head-tilt and chin-lift position, stabilized by shoulder rolls and neck cushions. The initial length of the NPA is estimated by placing the distal tip of the NPA extraorally at the angle of the mandible and measuring the distance to the labial commissure to determine the proper insertion depth (Figure 1). Alternatively, the anesthesiologist may measure the NPA against an appropriately sized Guedel OPA as an additional reference for insertion depth. Use of an NPA with an adjustable flange, with the moveable flange positioned according to the labial commissure/mandibular angle measurement, can help facilitate proper insertion depth (Figure 2). With a bite-block in place, the tongue is pulled forward or extruded, the patient's airway is suctioned, and the NPA is placed to the measured depth. The O-NPA may be placed lateral or buccal to the bite-block (Figure 2). A laryngoscope may be used to verify the supraglottic position of the O-NPA if necessary. Auditory verification of the patient's breath sounds and feeling the passage of air through the O-NPA when the patient inhales and exhales confirms its effective position. Alternatively, an end-tidal carbon dioxide (EtCO₂) sampling line may be qualitatively used to confirm the O-NPA's effective position (Figure 3a). To supply supplemental oxygenation, a cut nasal cannula is threaded down the O-NPA. Care must be taken to ensure that it does not exit the distal end of the O-NPA (Figure 3a and b). One or 2 folded pieces of 4 × 4 cotton gauze should be gently placed around the O-NPA as a shield to protect from aspiration of any extraneous dental debris and/or fluids (Figure 4). When properly placed, the distal/inferior end of the O-NPA should rest just beyond and below the base of the tongue, with the distal tip approximately 10 mm above the epiglottis.¹ Gentle placement may be further assisted with use of Magill forceps or cotton pliers to avoid trauma to the posterior oropharyngeal mucosa. At an appropriately measured insertion depth, the O-NPA should not contact or stimulate the vocal cords. Selection of a sufficiently rigid NPA will prevent NPA lumen collapse or deflection. An NPA with an internal diameter of 7 to 9 mm is suggested for use in an adult patient. Its position may be secured with tape in a similar manner commonly used to secure an oral endotracheal tube (Figure 5). Active high-volume suctioning of fluids and dental debris and active replacement of the soiled 4 × 4 cotton gauze throat shields with new gauze throat shields are employed throughout the procedure to achieve and maintain a dry, isolated operation field. At the end of the dental procedure, the O-NPA should be removed along with throat shields, debris, and fluids to ensure the airway is clear while the bite-block is in place. The O-NPA should not remain while the patient awakens because it will irritate the gag reflex and could potentiate a laryngospasm. For this reason, the timing of the O-NPA removal should precede entry of the patient into stage 2 of anesthesia depth.² Assistive airway maneuvers (eg, head-tilt, chin-lift, jaw-thrust) are usually sufficient to support the patient during emergence and recovery.

Figure 1.

Extraoral sizing of an oral placement of a nasopharyngeal airway measured from the angle of the mandible to the labial commissure (marked with a permanent marker).

Figure 2.

Oral placement of a nasopharyngeal airway, buccal to a bite-block. Note that the supplemental oxygen line in place only, no capnography sample line, adjustable flange is placed as a reference at the labial commissure.

Figure 3.

(a) Setup of cut nasal cannula and EtCO₂ sampling line threaded through a 32–34 French NPA. (b) Adjusted nasal cannula threaded through a nasopharyngeal airway without EtCO₂ sampling line.

Figure 4.

A 4 × 4 cotton gauze throat shield creates a dry, isolated operation field.

Figure 5.

Securing the oral placement of a nasopharyngeal airway (O-NPA) near the labial commissure with silk tape. At one end, the silk tape is split in half, lengthwise, up to a midway point. The “legs” of the tape are wrapped around the O-NPA to secure its position. Alternative taping methods similar to those used when securing endotracheal tubes is possible.

DISCUSSION

Anatomy of the Unconscious Patient

Airway obstruction under nonintubated DS/GA can result from movement or displacement of the anatomical structures once the patient is rendered unconscious. Several possible mechanisms involved include the passive closure of the glottis, passive posterior movement of the soft palate against the posterior pharyngeal wall, posterior displacement of the tongue, movement of the epiglottis against the posterior pharyngeal wall, lateral collapse of the pharyngeal walls, or any combination of the above.³ Positioning or displacement of the tongue is a key factor for upper airway obstruction, and management techniques that reposition the tongue anteriorly can help alleviate this issue and reestablish airway patency.³ Physical manipulation of the patient including head-tilt, chin-lift, and jaw-thrust maneuvers reposition the mandible, tongue, and hyoid bone into a more anterior position to create space, reestablishing and ensuring airway patency. Airway adjuncts that introduce an artificial lumen, such as an OPA or NPA, bypass the upper airway obstruction caused by the musculature of the tongue laying on the posterior wall of the oropharynx, thereby achieving airway patency by mechanically stenting the airway passages open (Figure 6). Mouth opening during dental procedures also increases airway collapsibility during DS/GA.⁴

Figure 6.

Sagittal view demonstrating oral placement of a nasopharyngeal airway (bite-block not shown) and nasal hood setup.

The O-NPA requires prudent measurement and precise placement to avoid inferior impingement of critical airway and laryngeal anatomy (Figure 7). If the O-NPA is advanced too inferiorly, or if it is too long, it can become seated in the piriform sinus or recess, which is located inferior to the lateral glossoepiglottic folds on either side of the larynx, or it can stimulate the vocal cords directly. Adequate anesthetic depth should therefore be maintained while correct placement of the O-NPA is achieved in order to mitigate cough and gag reflexes as well as minimize the risk of laryngospasm. Improper advancement or placement of the O-NPA may also cause it to pass anteriorly into the vallecula, where paradoxical airway obstruction can occur.

Figure 7.

Critical upper airway anatomy and possible placements of the inferior end of an oral placement of a nasopharyngeal airway (regions indicated by “x”).

Physiologic Control of Breathing Route

The physiological mechanisms of oronasal ventilatory control have not been fully elucidated.⁵ Mouth breathing occurs during exercise or with the development of nasal obstruction. In normal subjects at rest and awake, the transition from pure nasal to oronasal breathing occurs at an external inspiratory resistive load of 0.67 Pa·cm⁻³·s^–1, and the transition from oronasal to pure mouth breathing occurs at an external inspiratory resistive load of approximately twice that of the threshold load.⁵ It is suggested that pressure receptors in the nose and upper airway function to switch breathing modes based on inspiratory resistive loads.⁵ The effect of DS/GA on these mechanisms remains unclear; however, extrapolations can be made. It is known that nasal obstruction increases bilaterally due to vascular engorgement when a patient is supine in the dental chair.⁶ Susceptible patients who have clinically significant nasal obstruction have increased sleep-disordered breathing events, including mouth breathing.^6,7

The soft palate plays a critical role in directing airflow. During nasal breathing, the OPA closes when the soft palate moves antero-inferiorly against the dorsum of the tongue. During mouth breathing, the NPA closes when the soft palate moves posteriorly against the posterior pharyngeal wall. According to computed tomographic imaging studies of supine patients, the retroglossal-hypopharyngeal area is comparable between oral and nasal breathing.⁷ Upper airway restrictions, or upper airway collapse, occur at the retroglossal-retropalatal regions when the tongue displaces postero-superiorly.⁷ Furthermore, opening the mandible leads to shortening of the upper airway dilator muscles situated between the mandible and hyoid bone, thus negatively affecting the retroglossal diameter.

The ineffectiveness of an NPA in a patient who mouth breathes may be attributed to the high airway resistance encountered by a constricted nasal passage. When the distal/inferior end of the O-NPA is positioned at an equivalent level to that of a NPA, the greater combined airway diameter of the O-NPA and the surrounding oropharynx becomes the path of least resistance. Consistent with Poiseuille's law, the passage of air through the O-NPA will predominate over the NPA, assuming air flow resistance is lower through the O-NPA as the patient breathes. Nasal breathing and mouth breathing are not mutually exclusive in individuals who demonstrate sleep-disordered breathing patterns.⁶ These individuals can demonstrate oronasal breathing.⁶ Supplemental O₂ delivered by nasal hood would still assist oxygenation by apneic oxygenation strategy. The dynamic nature of nasal breathing and mouth breathing is a complex phenomenon with multiple factors likely at play.

End-Tidal Carbon Dioxide Monitoring

End-tidal carbon dioxide monitoring adds safety to procedural DS/GA and helps to detect hypoventilation, apnea, and acute respiratory events.^8,9 Studies have shown that abnormal EtCO₂ findings are detected before clinically observed changes or oxygen saturation (SpO₂) changes.^8,9 The O-NPA technique allows for EtCO₂ monitoring in 2 ways. Use of EtCO₂ may be facilitated by placing a nasal cannula with sampling capabilities on the patient, with or without a nasal hood, and connecting it to the monitor's capnograph. A second method requires cutting the same style nasal cannula line, typically removing the nasal prongs, and threading the cut nasal cannula line down through the O-NPA (Figures 3a and b) and then connecting the sampling line to the monitor's capnograph. One technique may offer better EtCO₂ detection than the other and has been observed to be case dependent. Satisfactory use of EtCO₂ detection has been observed to be dependent on the patient's tendency to nasal breathe or mouth breathe. For patients who fractionally nasal breathe, the nasal prongs are likely to function well. For patients who predominantly mouth breathe, the cut nasal cannula threaded through the O-NPA is likely to function better. The quantitative capnography measurements are typically difficult to interpret mainly because of a lack of a closed sampling system, which permits the influx of room air, causing dilution of the air sample. In an open system such as that with a nonintubated patient, EtCO₂ monitoring tends to provide more meaningful qualitative assessments.

Indications

The O-NPA technique is acceptable for dental procedures when endotracheal intubation is not necessary. In patients for whom there is difficulty maintaining adequate oxygenation and ventilation despite the combined use of supplemental oxygen and conventionally placed NPAs, the O-NPA technique may be considered. Preoperative assessment of appropriate patients may identify unfavorable airway findings, such as high Mallampati score, narrow interincisor clearance, history of sleep apnea, snoring, or a high STOP-BANG score.¹⁰ Patients who have findings of obesity, mandibular retrognathia, maxillary hypoplasia, macroglossia, nasal obstruction, abnormal nasal anatomy, high risk of prolonged or significant epistaxis (eg, patients on anticoagulants), or demonstrate mouth-breathing behaviors may benefit from this alternative airway technique.

Contraindications

This technique would be contraindicated in situations in which the use of a supraglottic airway device would be otherwise contraindicated. These include increased risk of pulmonary aspiration, suspected or known abnormalities or pathologies in the supraglottic anatomy, or minimal or moderate sedation.

Advantages

The equipment apparatus (Figure 3a and b) directs a continuous high-flow oxygen (O₂) supply into the oropharynx, which helps prevent desaturation through the physiological mechanism of apneic oxygenation. During apnea or the hypoventilatory pause between inhalation and exhalation, the alveoli maintain the ability to participate in gas exchange, whereby oxygen can be readily absorbed. By maintaining high-flow oxygen levels throughout this period, the previously established functional reserve capacity can therefore be replenished since high O₂ content in the airway would be constantly present.¹¹ The maintenance of oxygenation and the extension of time before oxygen desaturation occurs during disruptions in ventilation are key advantages of this technique. In the obese population, apneic oxygenation is effective in improving arterial O₂ saturation and increasing the time before critical stages on the oxyhemoglobin saturation curve are reached.¹² Typically, apneic oxygenation is achieved with a nasal cannula at high flow rates (15 L/min) in combination with a face mask and an adequate seal in order to create enough positive pressure to stent the airway and permit delivery of the O₂ source prior to and during intubation.¹³ Similarly, these concepts can be applied using a nasal cannula supplying supplemental O₂ within a nasal hood or directly through the proposed O-NPA technique with titrated O₂ flow rates ranging from 8 to 10 L/min (Figure 3a and b).

Disadvantages

The technique requires the careful placement of the O-NPA to its appropriately measured depth and is dependent on achieving and maintaining adequate anesthetic depth of DS or GA to mitigate the risk of laryngospasm or aspiration. Alternatively, topical lidocaine may be applied in the oropharynx preoperatively or intraoperatively to blunt the cough, gag, and laryngeal reflex when inserting the O-NPA.²

CONCLUSION

Use of the alternative O-NPA technique to deliver supplemental oxygenation and help airway patency is an effective airway management strategy for challenging airways prone to disruptions in ventilation and oxygenation during dental procedures using DS or nonintubated GA. The described technique is a minimally invasive and cost-efficient alternative approach.