A 60-year-old male has been in the post-anesthetic care unit (PACU) for 6 hours with a slowly expanding neck hematoma following an uneventful left carotid endarterectomy under general anesthesia. Over the last 45 minutes he has started to complain of difficulty with his breathing. Neurosurgery has booked him to return to the operating room (OR) for wound exploration and evacuation of hematoma. He is a smoker, takes medications for hypertension, hyperlipidemia, and type 2 diabetes mellitus, and was noted preoperatively to have reassuring airway anatomy. Post-induction at the original surgery, he was documented to have been easy to ventilate using a bag-mask, presented a Cormack–Lehane (C/L)¹ Grade 1 view at direct laryngoscopy using a Macintosh #4 blade, and the trachea was easily intubated with an 8.0-mm internal diameter (ID) endotracheal tube (ETT).

In the PACU he is now sitting upright, breathing oxygen at 10 L·min⁻¹ via a non-rebreathing facemask. Although restless, he is rational, complaining of dyspnea, dysphagia, and neck pain. Blood pressure is 180/95 mm Hg, heart rate 100 beats per minute, respiratory rate 30 breaths per minute, and his SpO₂ is 95%. He is audibly stridulous. Under a blood-stained dressing, the left side of his neck looks visibly enlarged and discolored. The patient is 5′10″ (178 cm) in height and he weighs 230 lb (105 kg). He has vascular access. An OR is being prepared for his return.

In What Ways Might This Patient Present Difficulty with Airway Management? What Are Key Aspects of the Airway Examination in This Situation?

This is an urgent situation. The patient must be quickly assessed and decisions made. Although some patients with neck hematomas are simply observed, case reports attest to difficulty in predicting if or when these individuals will go on to sudden and catastrophic airway obstruction.^2–4 As part of the patient’s evaluation, a formal airway examination should be performed, seeking predictors of difficulty in all aspects of airway management.⁵ Even though the patient’s anatomy presented no difficulty with airway management earlier that day, the presence of a neck hematoma changes everything. With evidence of obstructing pathology in the airway as manifested by stridor, neck swelling, and the patient’s dyspnea and agitation, difficulty can now be anticipated with all of bag-mask-ventilation (BMV), direct and indirect laryngoscopy and tracheal intubation, use of an extraglottic device (EGD) and potentially, even open cricothyrotomy as external landmarks become shifted or indistinct.

As situation acuity will often not permit diagnostic imaging of the patient presenting with obstructing pathology, if patient cooperation allows, useful information may be obtained by performing nasopharyngoscopy immediately before attempts at securing the airway.^6,7 This is generally well tolerated, and can provide information about any lateral displacement of the larynx, the degree of perilaryngeal edema, or location and size of an obstructing mass that may impede laryngoscopy, flexible bronchoscopy, tracheal intubation, or successful EGD placement.

What Other Patient Factors May be Relevant in This Situation?

With predicted difficulty in all aspects of airway management limiting options in this patient, an awake approach at securing the airway is preferable. However, for awake airway interventions, patient cooperation is generally needed. Patient cooperation may be lost (a) as hypoxemia occurs and/or (b) the patient panics as dyspnea worsens with progressive airway lumen narrowing. This speaks to the need for early identification of the patient requiring reintubation, while cooperation is retained. Sedating a less cooperative patient with a tenuous airway is hazardous and may itself precipitate complete airway obstruction.^8,9 Other patient comorbidities will assume secondary importance compared to the gravity of threatened loss of the airway.

What Are the Causes of Airway Obstruction in a Patient with a Postsurgical Neck Hematoma?

Neck hematomas tend to originate from venous or capillary sources more often than arterial bleeding.^10–12 Although arterial bleeds may present earlier or more quickly,¹⁰ neck hematomas arising from a venous or capillary source can be insidious and just as devastating in their ability to cause airway obstruction. The following mechanisms may contribute to the development of symptomatic airway obstruction in the patient with a neck hematoma:

1. 
   

   Physical pressure effect. The presence of a hematoma in the neck can mechanically displace the laryngeal inlet away from the midline position.^4,10,13–15 In addition, the lumen of the pharynx can be physically compressed by a hematoma, as it is unprotected by a bony or cartilaginous framework.¹⁶ It follows that some authors have considered significant compression of the larynx and trachea by a hematoma to be unlikely due to their rigid cartilaginous structures.^17,18 However, in a human cadaver study, Thakur and colleagues¹⁹ found that a mean pressure of only 136 mm Hg (i.e., within physiologic range) completely collapsed the trachea when applied in an oblique direction. In addition, even if the cartilaginous framework remains intact, the posterior, membranous portion of the trachea may be significantly compressed by a hematoma.²⁰ Case reports have indeed been published that include CT scan images of significant tracheal compression by hematomas.^21–22 Bukht and Langford²³ described a case in which an adult patient with a neck hematoma was intubated with difficulty with a 5-mm ID ETT. No leak was apparent even without ETT cuff inflation, however upon subsequent release of the hematoma, a large leak immediately developed. Such reports and studies suggest that physical compression of the trachea or larynx can indeed occur with a neck hematoma, in addition to lateral displacement.

   
   
2. 
   

   The development of perilaryngeal edema. This is a consistent feature in case reports of patients with neck hematomas^{2–4,10,14,21,23–27} and is often out of proportion to any degree of externally visible neck swelling or discoloration. Most authors agree that this is due to interference with normal venous and/or lymphatic²⁸ drainage by both the neck hematoma itself as well as blood tracking into interstitial tissue away from the site of the original hematoma.^{4,17,21,25,29,30} Release of tissue inflammatory mediators may also contribute.^29,31 At direct laryngoscopy, the resulting edema is variously described as “swollen supraglottic mucosal folds”^4,10 or a “watery, pale swelling of the mucosa” (Figure 57–1)^17,25 which in many cases substantially obscures the glottic opening. Interestingly, some published case reports have documented the development of similar perilaryngeal edema after neck surgery even without an obvious hematoma.^10,32

   
   
3. 
   

   Blood dissection along tissue planes in the neck. The parapharyngeal space is contiguous medially with the retropharyngeal space,²⁰ which in turn extends from the skull base to the upper mediastinum.³³ The parapharyngeal space also communicates anteriorly with pretracheal and submandibular spaces as well as subcutaneous tissues.³³ Blood from a neck hematoma in any of these areas can thus spread remotely from its initial location to further compromise the airway. Retropharyngeal collections of blood are often manifested symptomatically by neck pain and dysphagia or odynophagia in addition to hoarseness and dyspnea.³⁰ Retropharyngeal hematomas can cause airway obstruction by compression of the arytenoid cartilages, which may in turn adduct the vocal cords.³⁴ In addition, retropharyngeal swelling can render direct laryngoscopy more difficult by (a) shifting the laryngeal inlet anteriorly and (b) as it can be a large, dark mass, a retropharyngeal hematoma can absorb light from the laryngoscope, worsening visibility.³⁵

It should be noted that although the surgical incision should be reopened immediately in the patient in respiratory extremis, edema and remotely tracking blood will not remit promptly upon evacuation of clot, accounting for the variable success of this step in alleviating the patient’s symptoms.

Three other factors can also potentially contribute to postoperative airway compromise in patients undergoing routine head and neck surgery:

1. 
   

   Large volumes of fluid administered intraoperatively can exacerbate airway edema.

   
   
2. 
   

   Simply undergoing certain operations in the head and neck region may transiently cause narrowing of the upper airway, even in the absence of a neck hematoma. Carmichael and colleagues demonstrated a significant loss (up to 32%) of airway volume after routine carotid endarterectomy, greatest in the region of the hyoid but also present at the level of the arytenoids and cricoid ring.^36,37

   
   
3. 
   

   Neck surgery can result in transient palsies to cranial nerves (IX–XII)^38,39 due to direct injury during dissection, retractor pressure, or other causes.⁴⁰ If unilateral, such palsies may be asymptomatic; however, particularly in patients with a history of previous neck surgery or presenting for staged bilateral procedures (e.g., carotid endarterectomies), bilateral nerve damage can result in complete airway obstruction. Vocal cord palsy can result from damage to the vagal trunk or its recurrent laryngeal branches, while bilateral hypoglossal nerve palsies can result in airway obstruction from loss of innervation to the intrinsic muscles of the tongue and pharyngeal musculature.³⁸ One final point to note in the patient undergoing staged bilateral carotid endarterectomies is that ablation of the carotid bodies bilaterally can result in loss of the ventilatory response to hypoxemia.⁴¹

Pending the Decision of Whether and Where to Reintubate, How Can the Patient be Symptomatically Temporized?

It should be reiterated that patients with partial airway obstruction are unpredictable in when, where, and if they will go on to complete airway obstruction. Indeed, some case reports document a decision to conservatively manage neck hematoma patients by observation, only to be confronted with sudden and catastrophic airway obstruction some hours later.^3,4 In addition, patients going on to complete airway obstruction in this setting can do so without first developing the physical sign of stridor.^2,3,10 It follows that nursing staff and airway practitioners must be educated to recognize the early signs of impending obstruction from a neck hematoma (or airway edema from any cause), including subtle voice changes and hoarseness, with later progression to agitation, dyspnea, and eventually stridor. Stridor, a late sign of airway compromise, is variously considered to be a sign of an extrathoracic airway narrowed by 50%⁴² or to a diameter of 4 mm or less.⁴³ The patient in the presented case should be assumed to be near respiratory extremis. Once compromising airway edema from a cause such as a neck hematoma is suspected, the wound must be fully opened, plans formulated for securing the airway, and surgical reexploration initiated.

To temporize a case such as this on the short term (e.g., while organizing a return to the OR, or while obtaining equipment for reintubation), a number of maneuvers can be undertaken:

1. 
   

   Fully open the wound. Some,^23,44 but not all,^10,25,45 case reports document rapid clinical improvement following this maneuver. While a significant hematoma mass may be decompressed immediately, associated laryngeal edema and/or blood tracking remotely from the hematoma site will resolve more slowly. Clinical judgment dictates where and when to open the neck wound: the patient in respiratory extremis should have it opened immediately, while others may be safely managed upon returning to the more controlled conditions of the OR, especially desirable if an arterial origin is suspected. In general, any attempt at tracheal intubation should be preceded by release of the neck wound, whether in or out of the OR. This directive should be tempered by clinical judgment: for example, if a breach of the arteriotomy site is suspected after carotid endarterectomy based on a history of a rapid-onset neck swelling, management should parallel that recommended for the patient with penetrating neck trauma, in whom the possible presence of damaged major vessels mandates securing the airway by tracheal intubation prior to neck exploration.

   
   
2. 
   

   The head of the bed should be elevated, anywhere from 30 degrees to fully sitting,⁴⁶ to promote venous drainage and improve the mechanics of breathing. The patient with significant airway compromise will most likely naturally wish to assume the sitting position.

   
   
3. 
   

   Heliox can be administered. Heliox, a mixture of helium gas with oxygen, is less dense than air or pure oxygen. With its lower density, a helium–oxygen mixture minimizes the work of breathing by converting some or all of the turbulent flow through and distal to a critically narrowed airway to more laminar flow.^47–49 Heliox is available in different oxygen/helium dilutions from 20/80 to 40/60: to maximize its clinical effect, the mixture with the highest concentration of helium should be used that is consistent with adequate oxygenation. Improved flow with heliox can lead to larger tidal volumes and less alveolar shunting, sometimes resulting in improved oxygenation.^47,50–52 In addition, as a patient breathes more easily with alleviation of dyspnea-associated anxiety, the lessened negative inspiratory pressure applied to the obstructed area may result in less airway collapse, thus actually improving the degree of obstruction.⁴⁷ Thus, Heliox use in the patient with a critically narrowed airway can provide significant symptomatic relief, in turn potentially improving patient cooperation. In the setting of a neck hematoma, however, it should be assumed that heliox has no definitive therapeutic effect and is strictly a temporizing agent.

   
   
4. 
   

   The use of epinephrine aerosols⁵³ and systemic steroids has been described for upper airway edema, however there is no published evidence of their short-term efficacy in the setting of neck hematoma-induced airway compromise.

Should the Trachea of This Patient be Intubated in the PACU or in the OR? How Do You Decide?

The short answer is that the patient with a neck hematoma is ideally reintubated in the clean, controlled conditions of the OR with the immediate availability of surgical equipment and staff for an “airway double setup” (Table 57–1) and immediate access to difficult airway equipment and expert help. Although the OR offers the option of an inhalational induction of anesthesia if required, the 4th National Audit Project (NAP4) report of airway-related morbidity and mortality from the United Kingdom reported a significant failure rate with this technique.⁵⁴ Ultimately the decision about reintubation on-the-spot versus a return to the OR will be tempered by the following factors:

1. 
   

   Is the patient in extremis? If so, the airway should be secured on the spot.

   
   
2. 
   

   If the patient is becoming increasingly dyspneic, is the rate of decline such that a return to the OR may be safely undertaken?

   
   
3. 
   

   How far is the OR from the patient’s present location and is the OR located on the same floor as the PACU?

   
   
4. 
   

   If the patient obstructs during transport to the OR, would it be possible to bag-mask-ventilate the patient? The extensive upper airway edema accompanying most neck hematomas is likely to make BMV impossible once the patient has an obstructed airway.

How Should Such an Airway be Approached, and Why?

Patients with significant narrowing of the airway due to pathological processes are in a dangerous situation. Onset of dyspnea, and then stridor, suggests critical airway narrowing, and in the setting of a neck hematoma should generally be regarded as signs of impending complete airway obstruction. In this patient, the airway assessment has suggested the potential for difficulty with BMV, direct and indirect (video) laryngoscopic intubation, EGD rescue ventilation, and surgical airway. If time and the patient’s clinical condition permit, evaluation of the upper airway may be obtained with nasopharyngoscopy. Following the application of topical nasal anesthesia, a flexible nasopharyngoscope is inserted through the nose to permit the evaluation of the glottis and surrounding structures for the degree of edema and deviation of the larynx. In one study of 138 patients with head and neck pathology presenting for elective surgery, preoperative nasopharyngoscopy resulted in a change in planned airway management in 26% of cases.⁷ “Awake look” direct⁵⁵ or video-laryngoscopy may also provide useful information. Regardless, careful consideration must occur on how best to proceed. A number of options exist:

1. 
   

   Local or regional anesthesia. One published case series in the surgical literature documents hematoma evacuation in eight patients under local anesthesia with no morbidity, which contrasted significantly from the 57% complication rate in seven other patients done under general anesthesia.¹¹ Hematoma evacuation and exploration using local, regional (or no) anesthesia may be feasible before the patient is significantly short of breath and is still able to cooperate.⁴⁶ However, regional anesthesia (e.g., superficial cervical blockade) may be difficult to perform if an enlarging hematoma obscures anatomic landmarks.¹⁰

   
   
2. 
   

   Awake open cricothyrotomy or tracheotomy under local anesthesia. Some authorities suggest that patients with advanced degrees of obstructing airway pathology, particularly those with lesions of sufficient size to preclude passage of even a small ETT, should have their airways secured with awake tracheotomy under local anesthesia.^42,56 In expert hands and with patient cooperation, this is a procedure that can be done relatively quickly and painlessly. Technical difficulty can be encountered if midline landmarks are shifted laterally or are obscured by an expanding hematoma. In addition, airway edema can also occur internally at the level of the cricoid ring, potentially impacting the ease of open cricothyrotomy.³¹

   
   
3. 
   

   Awake oral or nasal (translaryngeal) intubation. Awake translaryngeal intubation (via oral or nasal routes) confers the advantage of having a breathing patient who is maintaining and protecting the airway, and would be the method of choice by many experts in this situation. In the setting of a neck hematoma, distorted anatomy can be anticipated (see section “What Are the Causes of Airway Obstruction in a Patient with a Postsurgical Neck Hematoma?” in this chapter). In the awake patient, movement of swollen mucosal folds with inspiration and expiration and the location of bubbles during expiration may help locate the laryngeal inlet (Figure 57–1). An attempted awake intubation from above must, however, confer a high probability of success in order to outweigh the risk of loss of the airway during the attempt (which can happen even in expert hands).^8,33 The NAP4 study reported on 23 patients with head and neck pathology who were intubated with a flexible bronchoscopic technique. The attempt failed in 14, and of those, 4 had been attempted in the awake patient.⁵⁴ Attention to topical airway anesthesia (see section “Local Anesthesia of the Airway” in Chapter 3 as well as section “I Thought That Awake Endoscopic Intubation Was the Foolproof Gold Standard for Difficult Airway. Why Did the Patient Obstruct During Application of Topical Airway Anesthesia?” in this chapter), good flexible bronchoscopic equipment, and the expertise to use it will be necessary.^10,57 Alternatively, direct laryngoscopy has also been described for awake intubations in the setting of neck hematomas.¹²

   
   
4. 
   

   Inhalational induction. An inhalational induction has been espoused in a number of reports as an option to facilitate intubation of a patient with a neck hematoma.^10,28,33,42 However, during an inhalational induction, while spontaneous ventilatory efforts may continue, it must be appreciated that volatile anesthetics have deleterious effects on upper airway tone and patency similar to those of intravenously administered sedatives.^6,58 While the inhalational induction may be considered for the patient unable to cooperate with an awake intubation or tracheotomy, an airway double setup should be arranged, the neck wound should be opened before induction of anesthesia, and close attention should be paid to maximizing airway patency as the patient loses consciousness (Table 57–2). Inhalational inductions in the setting of neck hematomas in published case reports have been successful in some cases although often prolonged or difficult.^4,10,23,33 More recently, data from the NAP4 study suggests that in the setting of obstructing pathology, this technique can and does fail. In 27 patients with head and neck pathology undergoing inhalational induction, there was no compromise to spontaneous ventilation in only 4 patients, some compromise with oxygen desaturation in 12, and in 11 patients, ventilation became impossible, either before or after laryngoscopy attempts.⁵⁴ At this time, inhalational induction cannot be condoned as the primary technique to facilitate reintubation in these patients, unless a lack of patient cooperation precludes an awake technique.

   
   
5. 
   

   Intravenous (IV) induction. For the cooperative patient, unless asymptomatic and an awake internal airway assessment has ruled out significant edema or laryngeal displacement, this route cannot be recommended as the method of choice to facilitate tracheal intubation with obstructing airway pathology due to a neck hematoma. IV induction of anesthesia with or without muscle relaxant administration is fraught with hazard in this setting with case reports attesting to the lack of any identifiable landmarks at direct laryngoscopy,^4,59 often in conjunction with the inability to bag-mask-ventilate the patient.^10,54,59

How Should We Proceed in This Case?

Our Plan A here is for an awake tracheal intubation under topical airway anesthesia, a viable option if good equipment and expertise is available with the flexible bronchoscope, and if patient cooperation can be enlisted. In the event of an uncooperative patient, an inhalational induction could be considered. If the patient were to obstruct during attempted awake intubation and a failed airway situation ensued, Plan B would be rapid conversion to an open cricothyrotomy.^60,61

How Will You Prepare for the Awake Intubation?

In the OR, an airway double setup should be readied (Table 57–1), with scrubbed surgical staff and equipment available for urgent tracheotomy or open cricothyrotomy. The difficult airway cart should be in the room. IV access should be assured, monitors applied, and the patient positioned in his position of comfort (often sitting). The cricothyroid membrane should be identified, marked, and disinfectant solution applied to the anterior neck. If not already done and if deemed appropriate, all layers^62,63 of the surgical incision should be opened and any easily accessible clot removed. Psychological preparation should be undertaken with confident reassurance that successful intubation will totally alleviate the patient’s dyspnea, while at the same time emphasizing the need for cooperation. If heliox had been applied, it should be interrupted for only brief periods during application of topical airway anesthesia. Topical airway anesthetic agents and techniques have been addressed elsewhere (see Chapter 3). Systemic sedation should be avoided if at all possible. An adult flexible bronchoscope (e.g., 6.2-mm OD) should be loaded with a small (e.g., 7-mm ID) ETT. An assistant can apply gentle tongue traction.

It is worth noting that even experienced anesthesia practitioner frequently fail to correctly externally landmark the location of the cricothyroid membrane. Studies with volunteer subjects have demonstrated an average success of less than 30% to 40% across gender and body habitus.^64–66 With neck anatomy altered by a neck hematoma, an even lower success rate ought to be anticipated. Ultrasound may be of use in identifying the location of the cricothyroid membrane as part of the airway double setup.

What Can You Expect During the Awake Flexible Bronchoscopic Intubation?

Awake flexible bronchoscopic intubation of the patient with extensive upper airway edema due to a neck hematoma differs substantially from that in a patient without obstructing pathology. In the patient with no obstructing pathology, navigation of the bronchoscope can proceed from landmark to landmark in the upper airway, for example, from uvula to base of tongue, to epiglottis, then to and through the glottis. In the patient with upper airway edema, both the epiglottis and glottic opening may be obscured by “clouds” of edematous tissue (Figure 57–1). This leaves tissue movement and the suggestion of an opening (e.g., bubbles on expiration) as the only indications of the path to the vocal cords (Figures 57–1A and B). As this happens, the bronchoscope is advanced in a slow and controlled fashion toward the opening or bubbles (Figure 57–1C). During inspiration, edematous tissues may be sucked together, obscuring the opening (Figure 57–1D). It is important to have the bronchoscope remain motionless in the airway during this phase, simply waiting for the view to reappear during the next expiration prior to resuming scope advancement (Figure 57–1E). Often in this setting, one simply continues navigating toward the opening suggested by movement until the cords suddenly appear in front of the scope (Figures 57–1F–H).

As the only landmarks leading to the airway after the uvula, presence of both movement and bubbles on expiration are crucial clues. This is one reason why it is critical to avoid ablation of spontaneous respiration in these patients.

It should also be noted that a neck hematoma can significantly displace the larynx to the left or right of its expected midline location. This can be anticipated before beginning the bronchoscopic intubation by examining the front of the neck, looking or feeling for the location of the thyroid cartilage, or performing an internal airway evaluation by nasopharyngoscopy or oral video-laryngoscopy under local anesthesia.

During Application of Topical Airway Anesthesia, the Patient Obstructs—What Should You Do Now?

If the patient obstructs, common sense should prevail. You should do what you would always do to ventilate the apneic patient: attempt an airway-opening maneuver and perform BMV, using a two-person technique. An oropharyngeal or nasopharyngeal airway may be used, depending on the patient’s level of consciousness. PEEP should be applied during BMV to help stent open collapsed tissues and ease any laryngospasm.^6,58,67

What if BMV Fails? Should a Surgical Airway be Performed?

A failed airway situation has been defined as the inability to maintain adequate oxygen saturation with BMV and failure to intubate on at least one occasion (see section “The Failed Airway Algorithm” in Chapter 2). A single attempt at direct or video-laryngoscopic intubation should be made. If this is unsuccessful, a failed airway is declared, and the default response becomes a tracheotomy or open (scalpel) cricothyrotomy.^60,61

At Direct Laryngoscopy, Only Extensive Edematous Mucosa Is Seen, Along with the Tip of the Epiglottis, Deviated to the Right

If the patient is already unconscious from hypoxemia, it is worth performing a single chest compression during laryngoscopy to see if a bubble is produced indicating the entrance to the airway. With or without a bubble, a tracheal tube introducer or small styleted ETT can be blindly placed where the glottic opening would be expected to be, beneath the epiglottis. If this single attempt fails, however, the default maneuver is to proceed to a surgical airway in order to maximize the chances of salvaging a bad situation. Unfortunately and all too frequently, the decision to proceed with a surgical airway is made too late to salvage the patient.

What Is the Role, if Any, for an EGD Such as an Laryngeal Mask Airway?

An EGD such as a laryngeal mask airway (LMA) may fail to oxygenate the patient in this setting as (a) correct seating in the pharynx may be difficult due to retropharyngeal swelling or a displaced laryngeal inlet and (b) even if correctly seated, extensive edema at or above the level of the cords may preclude effective ventilation. However, several centers have reported successful oxygenation of patients with LMAs in failed airway situations due to neck hematomas^45,59,68,69 or other obstructing pathology.^70,71 This may occur as the EGD bypasses more proximal edematous and obstructing soft tissues, allowing positive pressure ventilation from a position immediately in front of the laryngeal inlet. While the correct response in the failed airway (can’t intubate, can’t oxygenate) situation is a surgical airway, it is worth a single attempt at EGD insertion while preparations are underway to proceed with a surgical airway.⁶¹

I Thought that Awake Endoscopic Intubation Was the Foolproof Gold Standard for Difficult Airway. Why Did the Patient Obstruct During Application of Topical Airway Anesthesia?

Loss of the airway during application of topical airway anesthesia^67,71,72 or attempted awake oral or nasal endoscopic intubation^8,45,54,73 in the patient with a neck hematoma or other obstructing pathology is well described. Apart from the natural progression of the disease process, this may occur for a number of reasons:

1. 
   

   Systemically administered sedative agents may provoke sudden and total obstruction.^8,58

   
   
2. 
   

   Laryngospasm during the airway topicalization process,^42,71,74 particularly in the patient with heavier degrees of sedation.

   
   
3. 
   

   Patient panic: As the dyspneic patient desperately tries to inspire, the high negative inspiratory pressure applied to an already narrowed, collapsible upper airway may contribute to complete collapse.^74,75

   
   
4. 
   

   Direct effect of local anesthetic agents on upper airway mechanoreceptors. The existence of laryngeal and supralaryngeal pressure and stretch receptors has been hypothesized, responsible for maintaining airway patency by responding to negative intraluminal airway pressure via increasing neural and muscular activity^76,77 (see section “Can Topical Lidocaine Anesthesia of the Upper Airway Cause Airway Obstruction?” in Chapter 3). The activity of such receptors can be affected or abolished by application of topical airway anesthesia.^76,77 This in turn can significantly affect inspiratory flow, even in normal individuals. Pulmonary function studies in healthy volunteers have demonstrated a significant reduction in maximal,⁷⁸ peak, and forced⁷⁹ inspiratory flow rates following topical airway anesthesia. Studies of the sleep-apnea population in whom topical airway anesthesia has been applied have also shown worsening of obstructive parameters. This is an underappreciated side effect of topical airway anesthesia and in the patient with a tenuous airway may be an important phenomenon to consider. It does not preclude proceeding with awake oral or nasal tracheal intubation with topical airway anesthesia, but does underscore the need for planning and an airway double setup. In addition, in any patient with significant obstructing airway pathology, awake tracheostomy or open cricothyrotomy should be considered as a primary technique.