Chapter 2. Approach to the Difficult Airway

A difficult airway exists in a patient when conventional face mask ventilation is problematic or tracheal intubation is difficult, requiring advanced airway skills for success. Patient factors such as micrognathia, a short neck, a large tongue, craniofacial abnormalities, pregnancy, and obesity are chronic conditions associated with a difficult airway but do not inherently define a difficult airway. Other conditions such as angioedema, epiglottitis, Ludwig's angina, retropharyngeal abscess, tracheal trauma, traumatic/expanding neck hematoma, and cervical trauma are examples of acute factors that similarly may cause a difficult airway condition to exist. When patients with any of these conditions develop dyspnea or respiratory distress, immediate action is required to avert life-threatening decompensation or permanent debility. Furthermore, these patients can present at any time: a patient with a penetrating neck injury may present to an ED without warning, or a long-term ICU patient with diffuse soft tissue edema and a beard may unexpectedly decompensate and require intubation. Therefore, in a variety of settings, clinicians must be prepared for rapid escalation of care and difficult airway management.

While either difficult bag–mask ventilation or difficult intubation occurs in approximately 5% of patients,1–3 a situation in which both bag–mask ventilation and intubation are difficult occurs concomitantly in much fewer patients.4 Of those, less than 1% of patients require a surgical airway for emergent management,5 a fraction likely due to advanced airway management skills of emergency physicians and intensivists, and further aided by the development of multiple tools for managing the difficult airway.

When new patients present in extremis, a detailed history is precluded. However, several historical factors portend a difficult airway and, if possible, should be rapidly determined:

1. History of oral, neck, or cervical spine surgery or irradiation

2. History of oral or neck tumor, cellulitis, or abscess

3. History of neck or mandibular arthritis or other joint immobility

4. Presentation as a result of oral, facial, neck, or cervical spine trauma

5. Use of anticoagulants or presence of a coagulopathy

Likewise, a focused physical exam of the head and neck should be performed. The LEMON mnemonic can help direct the physical exam to determine if the patient might have a difficult airway6:

1. Look externally and assess factors associated with a difficult airway: obesity, micrognathia, large tongue, long upper incisors, prominent overbite with protruding maxillary incisors or underbite with large mandibular incisors, short bull neck, poor dentition that could be dislodged into the airway, or evidence of trauma.

2. Evaluate with the 3-3-2 rule. The 3-3-2 rules states that with the mouth open the patient should be able to insert three fingers between the teeth (the interincisor gap or, for edentulous patients, the “intergingival gap”; Figure 2-1), has three finger breadths between the front of the chin and hyoid bone (the “hyomental distance”; Figure 2-2), and has two finger breadths between the hyoid bone and the thyroid cartilage (the “thyrohyoid distance”; Figure 2-3). Patients who pass the rule (i.e., meet all of the criteria) are more likely to be successfully intubated without complications, that is, are likely not to have a difficult airway.

3. Mallampati score assessment: with the patient seated, mouth wide open, tongue protruding, and neck in extension, the clinician looks into the mouth to visualize the tongue, tonsils, uvula, and posterior pharynx (Figure 2-4). Class I airways allow for visualization of the entire posterior oropharynx, soft palate, uvula, fauces, and tonsils, while Class II airways allow for visualization of the soft palate, some but not all of the uvula, and fauces. Class I and II airways are associated with successful intubations. Class III airways are characterized by visualization only of the soft palate and base of the uvula, and are associated with moderate difficulty during intubation. Class IV airways do not allow for visualization of any of the posterior pharynx and are associated with severe difficulty during intubation (and may be impossible to intubate using traditional techniques).

4. Obstruction assessment: determine if there is an upper airway foreign body, tumor, or other obstructing factors such as epiglottitis or Ludwig's angina. Three key signs are difficulty handling secretions, stridor (which occurs when <10% of normal caliber of airway circumference is clear), and a muffled voice.

5. Neck mobility assessment: neck mobility directly affects a clinician's ability to visualize the vocal cords during intubation. Normal patients should be able to touch their chin to their chest on flexion with a wide range of extension. Cervical spine trauma or immobilization can limit this mobility and subsequent visualization, as can conditions such as ankylosing spondylitis and severe rheumatoid arthritis.

The MOANS mnemonic should also be used to predict those who will be difficult to ventilate with a face mask6:

1. Mask seal should be good and not obstructed by factors such as a large beard or hindered by factors such as a large bite abnormality.

2. Obesity with either a small jaw or mid-face can prevent a good seal.

3. Age >55 years old is associated with difficult mask ventilation.

4. No teeth and consequent lack of “dental tone.”

5. Stiff necks can make it hard to position patients for proper ventilation.

For inpatients, either already in an ICU or decompensating on a regular floor, additional history may already be known. For patients who have already been intubated (such as postoperative patients, or patients who have already had an ICU stay), information may already be known about their airways. If the patient's condition allows, such information should be rapidly obtained, accepting the fact that factors since the last intubation may have negatively impacted the ability to intubate the patient (prior intubation with residual swelling, injury, or bleeding, significantly positive fluid balance leading to diffuse edema, recently reversed tracheostomy, etc.). For patients intubated in the OR, the anesthesia notes can be invaluable. Note the number of attempts, the device used, and the view obtained (often described with the Cormack–Lehane grade) Figure 2-5.

Although predictor variables such as the Mallampati score may be highly positively correlated with descriptors such as C-L view (the Mallampati score has a positive correlation with the C-L grade of 0.8–0.9),7 they are still only predictors. Since descriptors such as the C-L grade directly describe the laryngoscopic view, it is, perhaps, more accurate to use that information when available. Of course, C-L grades will not be available for ED patients or for many inpatients (such as nonsurgical patients). Furthermore, the C-L grade says nothing about the ease or difficulty of ventilating the patient with a bag-valve-mask.

Once determined that the patient needs emergent airway management, preparation should begin immediately. If possible, the ensuing events should be explained to the patient as well as reassurance provided since patient anxiety can complicate management. The patient should be positioned to align the three main axes: the laryngeal axis, the pharyngeal axis, and the oral axis (Figure 2-6). While positioning the patient, equipment can be checked, including the following:

1. Appropriately sized face mask

2. Respiratory bag connected to oxygen

3. Suction set up and ready

4. Laryngoscope light functioning properly; backup handle available

5. Multiple types and sizes of laryngoscope blades available

6. Multiple endotracheal tubes (ETTs) available

7. ETT loaded with stylet

8. 10-cm3 syringe

9. Confirmatory devices (end-tidal CO2 detector, esophageal detector)

Of course, communication with staff regarding medications and other orders is imperative.

Even when there is concern for a difficult airway, most patients can still be orotracheally intubated with traditional direct laryngoscopy (DL). In the event that the initial DL attempt is unsuccessful, other maneuvers should be considered and attempted:

1. Reposition the patient to properly align the airway axes.

2. Consider the B-U-R-P maneuver, whereby the operator manipulates the thyroid cartilage with his or her right hand, providing gentle (B)ackward, (U)pward, (R)ightward (P)ressure. If this technique results in visualization of the vocal cords, an assistant can hold the thyroid cartilage in that position while the operator proceeds with intubation. The BURP maneuver is associated with improved visualization of the glottis and subsequent successful intubation.8

3. A different laryngoscope blade may be tried. This may involve simply changing the size of blade being used, or it may involve changing the type of blade, for instance, from a Macintosh to a Miller blade. While the Macintosh blade seems to be preferred by most clinicians, it can be difficult to use in patients with a large or “floppy” epiglottis, in which case a Miller blade may result in better visualization of the vocal cords.

4. A patient's habitus or size may preclude advancing a large-sized tube. If the vocal cords are visualized but the ETT cannot be passed, a smaller ETT may allow a successful intubation.

While these maneuvers are being attempted, preparations should simultaneously be made for one or more alternative airway control modalities. These methods can be difficult to perform under the stress of a decompensating patient. Furthermore, since the modalities often involve additional, expensive equipment, they are not part of routine practice, and skills may deteriorate. Therefore, it is important that these skills be maintained, perhaps by semi-routine use on patients not expected to have a difficult airway, or by other means. It is reasonable that clinicians should master two or three of these “rescue” tools for use in the emergent setting.

One of the easiest difficult airway tools to use is the video laryngoscope (Figure 2-7). It has been shown to improve glottic visualization and, thus, success of intubation attempts.9 To use a video laryngoscope, the patient is positioned, the mouth opened, and the laryngoscope placed midline into the posterior pharynx. When using the video laryngoscope, the tongue does not need to be manually displaced as with traditional laryngoscopy. Then, rather than looking into the pharynx, the clinician looks at the video monitor while advancing the laryngoscope to identify the epiglottis and then the vocal cords. On visualization of the glottis, the ETT is then placed into the pharynx under direct visualization, but then advanced into the trachea through the vocal cords under video screen visualization.

Although use of a video laryngoscope requires the clinician to go from direct visualization of the pharynx to using the video screen for visualization of the glottis to direct visualization for pharyngeal placement of the ETT and back to video screen visualization for glottic placement, this approach is easy to learn because the manual technique is similar to orotracheal intubation with traditional laryngoscopy and direct visualization. Furthermore, this technique has been associated with improved visualization of the glottis10 and appears to be the most easy difficult airway tool to learn. This technique is also favored by many clinicians when intubating patients in cervical spine collars since the collar can be left in place, resulting in less spine movement during intubation. The biggest disadvantage, as above, is that without regular use, it remains easy to obtain good glottic visualization, but difficult to pass the ETT. These devices are also finding an increased audience in training programs, both for teaching purposes and because they allow the supervising attending to better monitor trainees.

The lighted stylet (e.g., Trachlight, Surch-lite; Figure 2-8) is another option for the intubation of patients with a difficult airway, especially when direct visualization is hindered due to trismus or obscuration due to copious secretions or bleeding. It involves intubation without direct visualization of the epiglottis or vocal cords, which is disconcerting to some clinicians. However, it can be more successful than traditional intubation under DL and may be used to rescue failed attempts.11,12

The lighted stylet is a semi-rigid stylet with a light on the end (Figure 2-9). With the patient positioned for intubation and the ETT preloaded on the stylet as with a traditional ETT, the lighted stylet is turned on and placed in the posterior pharynx, and then slowly advanced while the clinician observes the exterior, anterior neck for evidence of the light “shining” through the skin. It is important to note that the stylet is advanced without direct visualization of the pharynx or glottic structures. When the stylet is in the trachea, the light shines distinctly through the skin due to the thin tracheal membranes that allow for the transmission of light. On visualization of this light in the anterior midline of the neck, the endotracheal tube can be advanced followed by confirmation of appropriate tube placement using standard technique. If the stylet is placed in the esophagus, the light is either not seen or perceived as a diffuse “glow” rather than a distinct point of light, in which case the clinician must reposition the stylet until a distinct point of light is seen shining in the anterior midline of the neck.

Although the lighted stylet has been used as a rescue airway technique, it requires transillumination of the trachea and anterior neck that can be hindered by high levels of ambient light. Therefore, one should consider dimming the lights when performing this technique. Furthermore, clinicians must practice using the lighted stylet under controlled settings before emergent use since it is associated with an appreciable learning curve as compared with DL.13

The intubating introducer (e.g., Eschmann Introducer, SunMed Flex Guide, and Frova; Figure 2-10) is a semi-rigid, long stylet (typically >60 cm) with a bent, soft tip designed for use with anterior airways or the situation when direct visualization of the glottic structures is not possible (e.g., significant bleeding from trauma). In the past, the term “bougie” was used to refer to such introducers because a bougie dilator was used as one of the first such introducers. The Frova is a particular intubating introducer that also has a fenestrated tip to allow oxygenation when used with a bag–valve–adapter.

Once the patient is positioned for intubation, the intubating introducer is placed blindly in the posterior pharynx and slowly advanced toward the trachea, maintaining the bent tip in a midline, anterior-most position. The introducer is advanced blindly until two tactile sensations are appreciated, confirming placement in the trachea. The first is the feeling of the tracheal rings, which are appreciated as “vibrations” or “clicks” by the clinician. The second is resistance to further advancement, corresponding with arrival at the smaller airways (as opposed to the esophagus that would allow continued advancement to the stomach without resistance). Once tracheal placement is confirmed, the ETT is advanced over the bougie using the Seldinger technique, the bougie is withdrawn, and confirmation of placement can proceed using standard technique.

One technique for use as a routine rescue device is to always have an introducer immediately available, yet still in its sterile package (so if not used, there is no cost). If DL yields an airway with either visualization of only the arytenoids anteriorly or difficulty passing an ETT into an anterior airway, the operator may remain in place and simply request the bougie be opened and passed to him or her. Then under DL, the bougie can be placed, the laryngoscope removed, and the ETT passed via Seldinger technique as above.

The advantages of the intubating introducer include use for anterior airways, for those with obscured direct visualization potential for use with or without laryngoscopy, and ease of use by novice clinicians.14 On the other hand, it may be difficult to use in cases of tracheal trauma and may be relatively contraindicated in cases of angioedema where increased edema may result from triggering of the bradykinin/complement cascade.

Fiberoptic stylets (FOS, e.g., Shikani Optical Stylet, Bonfils Retromolar Intubation Fiberscope, Levitan FPS scope; Figure 2-11) include a fiberoptic device at the distal end of a metal stylet, designed to move the clinician's view from the mouth and posterior pharynx to the end of the FOS near the glottis. They can be rigid or semi-rigid and may contain ancillary ports, for instance, for instillation of oxygen during intubation.

Like the lighted stylet and intubating introducers, the FOS may be placed blindly in the posterior pharynx. Then, the FOS is advanced toward the trachea while visualizing the pharyngeal anatomy through an eyepiece at the proximal end of the stylet. Once the vocal cords are visualized, the stylet is advanced into the trachea and then the ETT is advanced over the stylet with confirmation of appropriate placement using standard technique.

Alternatively, the oral, pharyngeal, and laryngeal axes may be aligned using a laryngoscope similar to traditional DL. The FOS may then be placed and advanced, using the laryngoscope to separate tissues, but with visualization via the eyepiece at the proximal end of the stylet.

One technique involves a combination of DL and fiberoptics. It may be used for routine use, or limited for use in a suspected difficult airway. The FOS is loaded with the ETT and intubation is attempted via DL. If the cords are visualized, the intubation can proceed via traditional means, utilizing the FOS like a traditional stylet to place the ETT under DL. But, if the airway turns out to be a difficult airway and the cords cannot be seen, the operator can change his or her view from one of DL to looking through the fiberoptic eyepiece of the stylet. Intubation can then proceed in a fiberoptic manner as above (advancing the FOS through the cords, and then withdrawing the FOS leaving the ETT in place). This combination of a DL approach with fiberoptic backup has several advantages: traditional DL practice is maintained (especially important in teaching programs), using a laryngoscope to separate tissue and align the axes may facilitate the fiberoptic approach, and, finally, for a difficult airway the rescue device is immediately available (in fact, already placed). The disadvantage of this technique is the cost since most patients can be intubated with routine DL, yet the FOS will still have to be sterilized.

Overall, the advantages of the FOS include use in the case of anterior airways, potential for use with or without laryngoscopy, and cost, typically thousands of dollars less than a video laryngoscope. On the other hand, it has limited use in cases where direct visualization of the glottis is hindered by secretions or hemorrhage and requires some experience before emergent use.

Flexible bronchoscopes (Figure 2-11) are flexible, directable fiberoptic tools that allow for visualization of the airway anatomy with greater manual control than possible with an FOS. Unfortunately, the time required for setup and possibility of scope damage from patient biting limit the use of flexible bronchoscopes for rapid, emergent orotracheal intubation. However, when there is time to prepare for a semi-awake nasotracheal intubation, flexible bronchoscopes can be invaluable. This could be especially useful in patients with suspected epiglottitis, angioedema, or severe obstructive sleep apnea where traditional intubation would be difficult and a surgical airway challenging. It is better tolerated by patients and allows them to remain sitting up. Furthermore, for planned extubations in the ICU or OR where an emergent reintubation is possible in a suspected or known difficult airway, it is easily feasible to have all equipment set up and ready for use.

The patient can be prepared by administering intranasal, aerosolized phenylephrine and placement of a 6-0 ETT lubricated with lidocaine jelly into the nasopharynx. Then, with the patient sitting upright, the flexible bronchoscope can be advanced through the lumen of the tube into the posterior pharynx. From there, the flexible bronchoscope is advanced while visualizing the epiglottis and vocal cords with the eyepiece at the proximal end. Once the distal tip of the scope passes through the vocal cords, the ETT is then advanced, the scope removed, and placement confirmed using standard technique. If there is difficulty advancing the ETT into the trachea, it may be caught on the arytenoids, in which case rotating the flexible bronchoscope counterclockwise may overcome the obstruction and allow for advancement of the tube.

The main advantages of this technique are use with anterior airways, improved visualization, and ability to be performed in upright patients able to breathe on their own. Furthermore, the bronchoscope itself can be used to confirm placement, both visually and measuring amount withdrawn to determine distance from the carina, obviating the need for a postintubation chest x-ray. The main disadvantages are cost, setup time (typically 15–20 minutes), the need for greater operator/clinician skill, and need for clear visualization that can be obscured by secretions, hemorrhage, and obstructing masses.

When other methods for tracheal intubation have failed, retrograde wire intubation can be rapidly attempted while preparing for placement of a surgical airway. The anterior neck should be quickly prepped with Betadine or ChloraPrep, followed by rapid identification of the cricothyroid membrane (Figure 2-12). Then an 18-gauge needle should be placed through the cricothyroid membrane (Figure 2-13). Placement can be confirmed by aspiration of air, and the needle repositioned aiming cephalad. A guidewire can then be advanced through the needle into the oropharynx, where Magill forceps or alligators can be used to extract the distal tip of the wire out of the mouth. Once the distal tip is obtained and firmly grasped, an ETT can be advanced over the wire into the trachea with a Seldinger-like technique and placement confirmed using standard measures.

This technique often requires two operators—one at the neck and one at the mouth—and is invasive, but has less morbidity than a surgical airway when successful. However, it can be difficult, especially in patients with upper airway obstruction or poor visualization due to blood or secretions.

Although never studied in the setting of the emergent, difficult airway, ultrasound can help localize the tracheal rings and cricothyroid membrane. This may facilitate retrograde wire intubation by directing needle placement and confirming tube placement. In addition, when possible, a second operator can use ultrasound to confirm placement of the lighted stylet, intubating introducer, or FOS in the trachea prior to advancing the ETT.

When the clinician is unable to perform tracheal intubation for the patient requiring emergent airway management, several tools can be used to provide oxygen while preparing to place a surgical airway (e.g., crichothyrotomy or emergent tracheostomy; see Chapter 3). However, as none of these provide definitive airway management, they should only be used to bridge patients to a definitive airway.

The LMA (Figure 2-14) is often used by anesthesiologists in the controlled setting of the operating room for elective cases, but it is not ideal for emergent settings because it does not protect the airway from secretions, aspiration, blood, or mass lesions such as expanding hematomas. Furthermore, the LMA is ineffective in situations where there is an obstruction (e.g., epiglottitis, angioedema, tracheal trauma) and should not even be attempted in such cases. The LMA works by creating a seal over the larynx with a soft mask that allows for oxygen to be blown into the lungs, in a sense moving the bag–mask apparatus from the level of the mouth to the larynx.

The LMA is inserted “backwards” into the posterior pharynx and then advanced while being rotated forward, seating the LMA in the hypopharynx. Once this is done, the cuff is inflated and bag ventilation can be performed. Even if adequate oxygenation and ventilation can be provided with an LMA, the clinician must remember that this is not a definitive airway as the patient's airway is not protected from secretions, aspiration, blood, or mass lesions such as expanding hematomas. The LMA should only be used temporarily to provide oxygen while preparing to establish a definitive airway.

The intubating LMA (I-LMA) is a specific kind of LMA with a metal handle and an aperture in the mask that allows for passage of an ETT through the LMA into the trachea. The I-LMA is designed so that the tube aperture is above the glottis in most patients when the mask is seated in the hypopharynx. Thus, once the I-LMA is placed, a flexible ETT can be passed through the lumen into the trachea with confirmation by standard technique. However, this will not work in cases of altered anatomy or glottic obstruction.

The Combitube and King Airway (Figure 2-15) are dual-port, double-cuffed tubes designed for use in the difficult airway. They are placed blindly into the posterior pharynx and advanced, usually resulting in an esophageal intubation. If the esophagus is intubated, the distal cuff lies in the esophagus and the proximal cuff lies in the supraglottic space. The distal cuff is inflated to prevent air from entering the stomach and help block stomach contents from aspirating into the airway. The proximal cuff is inflated to prevent air from leaking out of the mouth and help block secretions from falling back into the trachea. A bag–valve setup can then be used to ventilate from the laryngeal port to laryngeal fenestrations that lie above the glottic opening between the two cuffs.

As with the LMA, even if adequate oxygenation and ventilation can be provided with a Combitube or King Airway, the clinician must remember that this is not a definitive airway because the patient's airway is not fully protected from secretions, aspiration, blood, or mass lesions. Unlike the LMA, there is no “intubating” version and, therefore, the Combitube or King Airway should only be used temporarily to provide oxygen while preparing to establish a definitive airway. The only exception is on the rare occasion when the tube is placed blindly in the trachea, in which case the pharyngeal port can be used to ventilate the trachea since it is continuous with the distal tip of the tube and essentially functioning as an ETT.

In the event that the clinician is unable to perform tracheal intubation and cannot provide oxygen via an LMA, Combitube, or King Airway, supplemental oxygen may be provided emergently via needle cricothyrotomy. However, by the time this is attempted, the clinician has only a few minutes in which to establish a surgical airway.

Once the anterior neck is prepped with povidone–iodine or chlorhexidine gluconate, the cricothyroid membrane is rapidly identified (Figure 2-12). An 18-gauge needle is placed through the cricothyroid membrane (Figure 2-13) into the trachea, which can be confirmed by aspiration of air using a syringe. Once this is done, the plunger is removed and a bag–valve–adapter is attached to the open end of the syringe. Then, using positive pressure, oxygen can be bagged through the needle into the lungs while preparing for a surgical airway to follow (see Chapter 3).

Clinicians can anticipate encountering a difficult airway 1–5% of the time and should be able to rapidly assess the likelihood of a patient have a difficult airway based on a directed history and physical exam. In the event that a patient has a difficult airway and requires emergent management, a number of maneuvers can be done to facilitate successful orotracheal intubation by traditional laryngoscopy. When these fail, clinicians should be familiar with available “rescue” devices and techniques to provide oxygenation and ventilation without the morbidity associated with a surgical airway.