Chapter 8. Direct Laryngoscopy

8.1.1 What Is the History and Evolution of Direct Laryngoscopy and Tracheal Intubation?

In the modern era, direct laryngoscopy is almost exclusively associated with tracheal intubation, even though the procedure was initially developed for diagnosing and treating laryngeal pathology. Following the development of mirror laryngoscopy in the 1800s (Czermark and others), Kirstein reported the first direct laryngoscopy in 1895.1 Over the next 20 years the basic tenets of the procedure were refined by surgeons interested in laryngeal examination and surgical exposure.

A step-wise approach, the focus on epiglottoscopy, recognition of posterior laryngeal landmarks, optimal positioning for laryngeal exposure, and the benefits of external laryngeal manipulation and head elevation, etc are all detailed by Chevalier Jackson in his 1922 text, Bronchoscopy and Esophagoscopy, A Manual for Peroral Endoscopy and Laryngeal Surgery.2

With the evolution of modern anesthesia, the original straight laryngoscope designs by ENT surgeons gave way to instruments specifically designed for tracheal intubation, such as the straight Miller blade (1941)3 and the curved Macintosh blade (1943).4 It was also in this time period that the modern design of a detachable blade and battery handle became commonplace.

Between the 1930s and 1970s many different laryngoscope blades were designed to facilitate intubation (eg, Wisconsin, Phillips, Guedel, etc), but the Miller and Macintosh models (albeit with some modifications) remain universally used, and in most settings, are the only laryngoscope blades available.

The development of flexible fiberoptics, subsequent attachment of fiberoptics to rigid blades (Bullard laryngoscope, Wu Scope, etc), and more recently video laryngoscopes (Glidescope, McGrath, Video MAC, etc) have narrowed the clinical role of standard, line-of-sight, direct laryngoscopy, and now there is a wide array of indirect visual devices for both diagnostic imaging of the larynx and tracheal intubation. Direct laryngoscopy remains the predominant method of tracheal intubation. Alternative devices, however, are being increasingly deployed for both routine and anticipated difficult laryngoscopy.

8.2.1 What Are the Principal Design Components of Laryngoscopy Blades and How Do They Work to Facilitate Endotracheal Intubation?

Laryngoscope blade design, light, and battery systems affect procedural performance since they impact on illumination, laryngeal exposure, and endotracheal tube (ETT) delivery. This holds true for both straight and curved laryngoscope blade designs, but because these designs function differently, there are different considerations (see below).

The principal components of a laryngoscope blade are the spatula (that passes over the lingual surface of the tongue) and the flange that is used to direct the tongue (Figure 8-1), a fluid-filled noncompressible structure, to the side of the mouth and into the mandibular space (the space below the tongue). This concept of mandibular space volume is particularly important in clinical practice as the practitioner evaluates for difficult laryngoscopy and intubation (see Chapter 1).

Straight blades, such as the Magill blade (see Chapter 1, Figure 1-1), were originally designed to pick up the epiglottis and elevate it directly, while the curved Macintosh-type blades are intended to be advanced into vallecula and indirectly elevate the epiglottis by applying pressure to the hyoepiglottic ligament. These factors illustrate two distinguishing features of these blade designs: that straight blades are inserted more deeply than curved blades; and that curved blades have an atraumatic tip design to reduce the risk of vallecular injury.

Because laryngoscopy was originally an operative technique where the practitioner needed their dominant right hand (85% of the population is right-hand dominant) to be free to operate, the laryngoscope became by default a left-handed instrument.

Laryngoscopy and intubation are performed through the right side of the mouth. The left hand is used to insert the laryngoscope blade into the mouth to expose the glottis. The right hand is then free to perform a variety of tasks including the insertion of an intubation aid (eg, Eschmann Tracheal Introducer, [ETI]), manipulate the larynx, lift the head, suction the airway, and ultimately, pass the tube.

Early pioneers employing straight blades recognized that tongue displacement to one side facilitated laryngeal visualization, particularly if the blade of the laryngoscope was inserted in the corner of the mouth and along the paraglossal gutter. Importantly, it was recognized that this paraglossal or retromolar technique optimized the laryngeal view mostly because it shortened the distance between the teeth and the larynx (ie, the molars are closer to the larynx than the incisors). The other benefit of right paraglossal laryngoscopy is that the rigid laryngoscope blade impacts the molar teeth rather than the relatively more fragile central incisors. The flange of the laryngoscope remains a threat to dentition and should never be leveraged backward against the teeth.

Straight blade laryngoscopes tend to have smaller displacement volumes (defined by the dimensions of the spatula and flange) than curved designs. It is logical, therefore, that straight blades (and a paraglossal approach) are favored in patients who have a small mandibular volumes into which the tongue is displaced (or compressed) during direct laryngoscopy. Examples of such patients are small children (below the age of 8, but especially below age 5) and adults who have a receding chin.

8.2.2 What Are the Variables that Determine the Illumination Created by a Laryngoscope Blade?

Illumination is critically important for direct laryngoscopy. Bright light is necessary for tissue edge and color discrimination, and the identification of tissues and structures. This is particularly important in preterm infants where the appreciation of subtle color differences is critical to intubation success.

Laryngoscope lighting systems can be divided into those with a light source mounted directly on the blade (bulb-on-blade), and those in which the light source is at the top of the handle (bulb-on-handle).

Bulb-on-blade designs (sometimes referred to as conventional blades) have a simple electrical connection between the bulb socket on the blade and the handle (with enclosed batteries). This connection is very robust and less subject to malfunction than the spring-loaded, on-off lights used with bulb-on-handle systems. These removable bulbs can usually be replaced if they fail. This feature confers the risk that should the bulb become loose it may flicker during operation, or worse yet, become dislodged and lost into the patient.5,6 To eliminate this risk, some manufacturers fuse the bulb to the blade rendering the bulb nonreplaceable.

Laryngoscope bulbs for both designs are of several types: incandescent filament (tungsten with halogen gas), xenon gas, and light-emitting diodes (LED). The bulb itself can have either a frosted or clear lens, and may incorporate a reflector (common with bulb-on-handle designs).

Compared to other light-producing systems, LED bulbs use very little energy, operate with less heat, and have a much longer life span, thereby eliminating bulb replacement as a major concern. They now can be produced at less cost than other bulbs and produce brilliant light. The light from an LED tends to be whiter and bluer than traditional bulbs. All of the newer intubation devices (video laryngoscopes, mirror laryngoscopes, chip-on-stick CMOS-imaging devices, etc) use LED lights.

With bulb-on-handle systems, a light-conducting fiber, made of either glass or plastic, conveys the light from the top of the handle to the distal portion of the blade. Although such blades are often called fiber-optic, they have no optical fibers, per se, and a more appropriate term is fiber-lit. Glass fibers conduct light more efficiently, but cost significantly more. Disposable blades commonly use a light-conducting bundle made of plastic, whereas nondisposable fiber-lit blades use glass fiber bundles. In the United States, any blade or handle that uses fiber illumination has a green dot on the blade base and a green circle at the top of the handle (commonly referred to as a green-line handle). It is important for practitioners to appreciate that fiber-lit blades and handles and conventional blades and handles are not interchangeable.

A critical and essentially unexamined area of laryngoscope illumination involves batteries.7

Alkaline batteries have a gradually declining discharge curve. Failure to appreciate and rectify this declining illumination may compromise direct laryngoscopy by low light, heralded by a difficult or failed intubation.

Lithium batteries have a much flatter, higher discharge curve than alkaline batteries, but fail precipitously once the energy output falls below a certain threshold. Lithium batteries are much more expensive and generate more heat than alkaline batteries.

Some manufacturers, especially those producing high-quality fiber-lit blades, offer nickel-metal-hydride rechargeable battery systems, which produce very intense light when combined with a xenon bulb and glass fibers. While the light output from these high-end fiber-lit systems is impressive, they are very expensive.

Newer LED technology has the potential to rival the light output of these systems at a fraction of their cost, draw little energy, and are offered in a single-use, disposable, bulb-on-blade design.

Regardless of the type of light, the intensity of light reaching the distal end of a laryngoscope blade is dependent on the distance the light must travel. This phenomenon is governed by the inverse square law of physics, that is, if the distance from the light source to an object is doubled, the resultant amount of light energy reaching the object is reduced to one quarter of the original amount. So, generally, blade designs with shorter light-to-tip distances create more intense distal light. This produces substantial variability in the amount of light emitted by different combinations of blades and handles used in clinical practice. In a study conducted in emergency departments, there was a 500-fold difference in light output between the best and worst blade-handle combinations.8

Few clinical settings monitor the light output with light meter testing. Lighting standards in dentistry or surgery recommend 5000 lux.9 While there is no well-accepted light intensity standard for the laryngoscopes, the International Organization for Standardization has suggested 700 lux as a minimum light output for laryngoscopes.10 In the presence of blood, secretions, and vomitus, common to emergency airways, more light is needed to discriminate landmarks.10

8.2.3 What Are the Distinguishing Features of Commonly Used Curved (Macintosh) Blade Designs?

The term "Macintosh blade" is generally used to mean any curved blade. However, since Macintosh's original description in 19434 several variations have been produced that are distinguishable by their flange height, flange shape, light position, and light type. These designs are commonly designated by their geographic manufacturing origins, that is, American (commonly known as "Standard"), English (commonly known as "Classic"), and German designs. The common features are a gently curved spatula and a large reverse Z-shaped flange (Figure 8-1).

American blades closely follow Macintosh's original description, that is, a large vertical, square-shaped, proximal flange that does not extend to the distal tip, coupled with a bulb-on-blade illumination system. The English design has a smaller, curvilinear proximal flange that runs all the way to the distal tip, and also uses a conventional light. Heine of Germany developed a fiber-lit blade that follows the English contour in terms of a short proximal flange. A large rectangular-shaped 5-mm glass fiber bundle is incorporated in the flange. The English and German designs have a much shorter light-to-tip distance than the American design (Figure 8-2). Most American designs use a frosted bulb, while most English designs have a clear lens. American and English designs now offer fiber illumination options. Numerous manufacturers around the world now offer American, English, and German curved blades, and many blades have a mix of features.

It is interesting to note that Macintosh envisioned one adult size for his blade (corresponding to approximately a Macintosh size 3). Market demand lead to the current variety of pediatric and adult sizes available. Size selection is largely a matter of patient size and practitioner choice. No matter the size chosen, it should be noted that the most common error of the novice is inserting the blade too deeply and into the upper esophagus before visualization is performed. The shorter light-to-tip distance (and light source common to German or English designs) also provides better illumination relative to the American design.

A recent variation of the Macintosh design is the McCoy (also known as Corazelli-London-McCoy [CLM]) levering laryngoscope blade (Figure 8-3). This blade is a Macintosh design with an articulating distal tip that when activated is intended to elevate the tissue at the base of the tongue (improving epiglottis lift and laryngeal exposure). This blade has become quite popular in the United Kingdom (where it originated), but published clinical investigations have reported mixed results.11-16

8.2.4 What Variations Exist between Miller Blade Laryngoscope Designs?

Robert Miller's straight blade design in 1941 adapted the straight shape of early laryngoscopes, in particular that of Magill (see Figure 1-1), but added a slightly upturned distal tip and narrower flange.3 The flange had a compressed D-shape (when viewed longitudinally) with a height large enough to accept a 37 French Argyle tube. Compared to tubular shaped blades (eg, Jackson-Wisconsin) the much shallower proximal flange was intended to minimize dental injury (Figure 8-4). The light was situated at the distal tip on the right side of the spatula, opposite the flange side, and tilted toward midline (Figure 8-1).

Since Miller's original description various manufacturers have compressed the flange height, and some have changed the bulb location (to the left flange edge, or recessed within the flange). Designs with light sources located on the exposed edge of the left flange are less preferred by some since a light at this location can become embedded in the tongue with resultant poor illumination. Most Miller designs currently made for adults cannot accommodate an adult-sized cuffed endotracheal tube down the barrel. In addition, tube passage down the barrel blocks the line-of-sight to the target. The very narrow design of modern Miller blades necessitates careful paraglossal placement (the small flange cannot sweep the tongue) and the extreme right corner of the mouth (which often requires manual retraction by an assistant) must be used for tube delivery. Alternatively, an ETI can be employed. Another challenge of the narrow-flange straight blades is that it makes landmark recognition down the barrel difficult.

8.2.5 What Is the "Straight Blade Paradox?"

Landmark recognition and ease of tube delivery improves as the flange height and spatula size of a straight blade is increased. Paradoxically, it gets harder to introduce the blade alongside the tongue, and reach the larynx, as the displacement volume of the blade increases. This was known to Miller, who shortened his flange height, but left the resulting D-shaped barrel large enough to accept an ETT.

Straight blade designs with larger flanges (and spatulas) than the Miller design include the Phillips (a two-third small C-shaped flange), Wisconsin (a higher, nearly full C-shaped flange), and the Guedel (a very large, sideways U-shaped flange and spatula) (Figure 8-4).

The Henderson straight blade has small incomplete two-third C-shaped flange that is large enough for tube delivery. It also has a uniquely visible distal tip (a knurled edge at the distal blade tip is visible when viewed down the barrel), and a large, recessed, fiber bundle light source (Figure 8-5).

8.2.6 Apart from the McCoy and Henderson Blades Already Mentioned, Are There Other Recent Blade Designs that Might Be of Use?

The Dorges universal blade is intended to replace Macintosh size 2 to 4 blades with one blade for all patients from age 1 to adult.17 The curve is much reduced, the spatula is tapered from proximal end to distal tip, and the proximal flange height is very short (15 mm), allowing it to be used with children and those with limited mouth opening, while at the same time permitting deeper insertion in larger adults owing to its length (Figure 8-6).

The Grandview blade is an emergency blade for adult patients that is available in two sizes.18 It combines a very wide spatula with a slight overall curve and a narrow proximal flange (Figure 8-7). The resulting blade can be used to lift the epiglottis directly or indirectly.

8.3.1 What Optical and Biomechanical Considerations Should Practitioners Appreciate When Performing Direct Laryngoscopy?

Direct laryngoscopy is a procedure with inherent visual restrictions. Visual restrictions are created by the degree to which the mouth opens, the teeth, the tongue, the long-axis view down a laryngoscope blade, and the structures about the laryngeal inlet that surround the glottic opening. Laryngeal anatomy, which is exposed in piecemeal fashion initially, must be recognized when viewed down this restricted visual space. In many instances, only a small posterior portion of the glottic opening may be visible. Passage of the ETT further adds to the visual challenge. It is critical for practitioners to know laryngeal anatomy in detail, to anticipate the sequence and appearance of structures as they come into view, and to be aware of how visual restrictions and biomechanics impact on laryngeal exposure and tube delivery.

8.3.2 What Is the Best Way to Maximize Mouth Opening and Jaw Distraction for Laryngeal Exposure and Tube Insertion?

As has been previously mentioned, employing the right corner of the mouth for laryngoscope blade insertion and tube passage is essential. A paraglossal approach is absolutely essential with straight blades. Even with curved blades, midline placement of the blade must be avoided because it will create tongue flop on each side of the blade, restricting glottic exposure and tube delivery.

The amount of mouth opening possible is a function of jaw distraction, and head and neck positioning. Positioning that facilitates jaw distraction and mouth opening is important in all patients, but most critical in the obese. Supine patients without cervical spine immobilization or known cervical pathology are optimally positioned for laryngoscopy when the external auditory meatus and sternal notch are horizontally aligned when viewed from the patient's side (see Chapter 18, Figures 18-1 and 18-2). This is called "ear-to-sternal notch" or "ramped position."

The traditional "sniffing position" is created by a combination of neck flexion and head extension at the atlanto-occipital joint. Ear-to-sternal notch positioning usually requires 8 to 10 cm of elevation under the occiput, generally much more head elevation than that produced by the standard sniffing position. Furthermore, standard sniffing position posture fails to take into account size-related anatomical variations of the respiratory tract as it transitions from the thorax through the head and neck. On the other hand, ear-to-sternal notch positioning takes this variation into account permitting external landmark-based patient positioning to be individualized. These anatomical variations are most frequently appreciated in individuals who are obese and morbidly obese. In such patients, a ramp may be several feet high and incorporate support under the upper torso and shoulders as well as the head to achieve proper alignment. Head elevation and ramping in this manner optimizes laryngoscopy, while at the same time offering improved gas exchange mechanics.

When performing laryngoscopy with the patient supine, along with ear-to-sternal notch positioning, the face plane of the patient should be parallel to the ceiling (see Figure 18-2). A common error is to overextend or tilt the head backwards.2 Atlanto-occipital extension may push the base of tongue and epiglottis against the posterior hypopharyngeal wall. Not only does this make recognition of the epiglottis more difficult upon blade insertion, this also narrows the space available to pass the laryngoscope and restricts laryngeal exposure. Extension alone may also create tension on the anterior neck muscles opposing simultaneous efforts to open the mouth and distract the jaw.

Successful laryngoscopy in this position requires that the patient's head be below the practitioner's xiphoid process, a position recommended by some texts. The reason for this is that increasing head elevation dynamically during laryngoscopy if laryngeal exposure is inadequate is made easier.19 Dynamic head elevation cannot be done on the morbidly obese and these patients must be ramped into a proper position in advance (see Figure 18-2).

Mouth opening in the anesthetized or unresponsive patient usually occurs with head and neck positioning. In the event it does not, it can be achieved by simply pushing the chin in a caudad direction or by employing the cross-fingered or "scissors technique." This technique provides a more controlled and effective force than simply extending the head on the neck.

8.3.3 What Is the Optimal Position for Laryngoscopy in Patients with Known or Suspected Cervical Spine Injury? Is It Safe to Perform Direct Laryngoscopy?

Direct laryngoscopy has been shown to be safe in patients with known or suspected cervical spine injury, but it should be performed with manual in-line immobilization (MILI) (see Chapter 15). There has been considerable attention and controversy regarding airway management in the known or presumed C-spine-injured patient.20-22 Some would argue that this concern has lead to unnecessary delay in managing the trauma airway, a decision which in some cases could result in increased morbidity and mortality (eg, hypoxemia and/or hypercarbia in head-injured patients). As a result, ATLS has backed away from an earlier recommendation that C-spine imaging precede airway management. Furthermore, there is little evidence to support secondary spinal cord injury directly attributable to airway management.21-23 Despite the fact that MILI does not completely prevent C-spine motion, it remains a recommendation. Care should be taken to ensure proper application of MILI in such a manner that mouth opening is not limited. Mouth opening is markedly limited with a collar in place where epiglottis only is visible (or worse). This can occur in more than 60% of cases.24 Properly performed MILI will reduce the incidence of an epiglottis-only view to 22%.25

Research comparing intubation devices have revealed no convincing superiority of any device over well-performed DL in terms of limiting C-spine motion.20 The major priority in managing suspected C-spine-injured patients is how to optimize view on laryngoscopy. Indicated airway management should not be delayed in fear of causing secondary spinal cord injury. The use of alternative devices, such as optical stylets or video laryngoscopy may help overcome a challenging view, although simple maneuvers, such as the application of optimal external laryngeal manipulation26 (OELM or BURP [backwards upwards rightwards pressure]27) and the use of an Eschmann tracheal introducer (commonly referred to as a gum elastic bougie) are equally effective in managing the trauma airway with suspected C-spine injury.20

Ear-to-sternal notch positioning cannot be used in such patients. The front of a cervical collar should be removed in order to permit jaw distraction. It is also helpful to drop the foot end of the stretcher while keeping the stretcher straight (ie, reverse Trendelunberg). This positions the airway higher than the stomach and may prevent passive regurgitation and improves pulmonary mechanics. An assistant must maintain MILI while laryngoscopy is carefully performed.

8.3.4 How Should the Laryngoscope Be Gripped to Minimize the Work of Laryngoscopy While Maintaining Fine Control of the Blade Tip?

The mechanics of laryngoscope lift are slightly different with curved versus straight blades. With the curved blade, the tip is guided into vallecula to depress the underlying hyoepiglottic ligament, lifting the epiglottis forward away from the glottic inlet. With straight blades, the tip of the blade lifts the epiglottis directly. Both curved and straight blade handles should be gripped with the tips of the fingers where the handle meets the proximal blade (Figure 8-8). The handle should be gripped low enough that the blade is essentially an extension of the forearm. Holding the handle higher increases the length of the lever arm requiring significantly more muscular effort. When properly gripped with the thumb pointing upward on the handle, fine control and effective mechanical advantage is achieved, and levering on the upper incisors is less likely to occur. Laryngoscopy is a delicate procedure, mostly dependent on gentle positioning of and correct vector forces at the blade tip. When properly positioned, the amount of force required for most patients is minimal and can be achieved by a light grip. When the blade tip is not correctly positioned, excessively forceful lifting will usually not correct the problem.

Another way to maximize lifting efficacy with minimal muscular effort is to keep the left elbow adducted to your side (roughly the anterior axillary line), not pointing outward. With the elbow in, the handle gripped down low, the forearm is kept straight and body weight can be used to rock forward slightly so that minimal arm strain occurs. Force is efficiently transferred along the forearm and down the long axis of the blade.

8.3.5 How Is the Larynx Sighted during Direct Laryngoscopy? Is Performance Improved by Assuming a Distance as Far as Possible from the Target?

Contrary to popular belief and traditional instruction, even with an extended arm position, it is not possible to simultaneously see the larynx during laryngoscopy with both eyes.28 This is due to the inherent visual restrictions of direct laryngoscopy, created by the opening of the mouth, the teeth, the tongue, the laryngoscope blade itself, and the structures of the laryngeal inlet. Visually, direct laryngoscopy is similar to looking down a narrow pipe at a target the size of a quarter, from a distance of 14 to 16 in.

Both eyes can be open during the procedure, but sighting of the larynx is with the dominant eye only; the brain subconsciously blocks out the nondominant image through a process called "binocular suppression." The same phenomenon occurs when looking through a peephole in a door, or when sighting during target sports. In situations without visual restriction, the right and left eyes have slightly different perspectives on an object, due to the distance separating the eyes in the skull. These slightly disparate views are fused into a single stereoscopic image. This cannot happen with the visual restrictions created during laryngoscopy; stereoscopic sight cannot be achieved. Because binocular suppression occurs subconsciously, even experienced laryngoscopists may not be aware of which eye they use to sight the larynx.

The monocularity of laryngeal sight during laryngoscopy is evident when viewing novice intubators attempting laryngoscopy for the first time by noting a subtle side-to-side head rotation, intermittently sighting the target with one eye and then the other.

The old adage that "experienced laryngoscopists maintain a distance from the target, while novices climb into the mouth" is due not to experience but rather restrictions on accommodation that occur with age. By the mid-forties, the near visual accommodation point begins to move out approximately 2 to 3 cm·y−1. By mid-fifties regardless of your underlying acuity, presbyopia results in the near focus point being at about arm's length. Younger practitioner's have the accommodation flexibility to focus on near objects. These changes are exacerbated in low light conditions. The amount of light needed for laryngoscopy by the same practitioner is different at age 40 versus age 50 and 60; more light improves the near focus ability significantly and is another reason for using laryngoscope systems with good light output.

8.3.6 Is It Beneficial to Identify Ocular Dominance, Acuity, and Accommodation Distance in Trainees and How Is This Done?

Ocular dominance, visual acuity, and accommodation should be assessed at the start of procedure training and in all practitioners on the steep curve of presbyopia (mid-forties).

Ocular dominance is tested by having the practitioner perform direct laryngoscopy on a training mannequin. After the practitioner confirms that the larynx is sighted, instruct him or her not to move their head. Selectively cover each eye, individually. When the nondominant eye is covered the laryngeal view is not compromised; when the dominant eye gets covered the larynx will no longer be sighted (or it will be seen partially, off angle). One cannot change one's natural ocular dominance. Eyedness tends to follow handedness assuming there is no unequal acuity, and since majority of the population is right-handed, most practitioners are also right-eyed. Persons who have a difference in visual acuity (wear lenses), or are left-handed, have a greater likelihood of being left-eyed when it comes to laryngoscopy.

Identification of ocular dominance, formal visual acuity, and accommodation testing is valuable to the trainee to proactively prevent procedural performance problems. Notwithstanding severe visual acuity problems, most accommodation issues can be addressed by corrective lenses. Unfortunately, many practitioners have lenses made for either driving, or reading, but not for the proper procedural distance of laryngoscopy. The proper procedural distance for a given practitioner is between their arm held at full extension, and the arm flexed at 90 degrees. For most practitioners this is about 14 to 16 in (35-40 cm). Corrective lenses become a valuable aid to direct laryngoscopy in most practitioners by their mid- to late forties.

8.4.1 What Factors Contribute to Difficult Laryngoscopy and How Reliable Is Prediction?

Difficult laryngoscopy can result from two different issues: (1) problems with landmark recognition; and (2) mechanical problems that prevent laryngeal exposure.

Landmark recognition is much more difficult in the presence of blood, secretions, vomitus, or distorted anatomy from a myriad of causes, including burns, edema, and other pathology. Successful laryngoscopy hinges on recognizing the epiglottis and structures of the laryngeal inlet, in addition to the glottic opening and vocal cords. The epiglottis has a mucosal appearance that is very similar to the posterior hypopharynx even without the additional challenges of fluids, vomitus, or distorted anatomy. Fluids from the oropharynx and hypopharynx will collect above the epiglottis when a patient is positioned in a supine position with poor muscular tone (or after the use of muscle relaxants). This can easily cause epiglottis edge recognition failure as the blade is inserted. Elevation of the epiglottis out of the fluids by proper jaw distraction during the first phase of laryngoscopy, which is, in turn, a function of proper head and neck position, and avoidance of overextension may help. Because fluids are often present in the airway, it is appropriate to have a Yankauer suction immediately available.

Mechanical problems that can limit laryngeal exposure include limited mouth opening, prominent dentition and overbite, a large tongue-to-pharynx relationship (ie, the Mallampati score), short thyromental distance (a small displacement volume for the tongue), and limitations of neck mobility. Although great effort has been put into devising scoring systems for predicting difficult laryngoscopy, the clinical utility of such screening tests remains very limited, more so in emergency situations. Only about one in three emergency patients who undergo intubation can follow simple commands, permitting even a basic screening assessment. Emergency patients with poor muscular tone, lying in a supine position, will almost universally have a poor and different Mallampati score and a short thyromental distance. Compounding this are those with suspected C-spine injury because they cannot undergo neck mobility testing.

As reviewed by Yentis,29 it is statistically challenging to devise an effective screening test, or combination of tests, for detecting a rare outcome (failed laryngoscopy). The trachea of a vast majority of patients can be successfully intubated with direct laryngoscopy, and unless a screening test has extremely high specificity and sensitivity, most predicted failures will be false positives. Conversely, some patients who would seem to be easy may be difficult or impossible because laryngoscopy primarily involves interaction with tissue not visible to oral inspection (the base of tongue and epiglottis, eg, lingual tonsillar hypertrophy).

While it is important to be aware of factors that can contribute to difficulty, screening performs poorly, and practitioners should always plan a means of rescue gas exchange and rescue technique should direct laryngoscopy and/or mask ventilation prove difficult or impossible.30 Much of the historical concern about difficult laryngoscopy is no longer relevant, now that there are so many alternative effective options for intubation, and even more significant, an extraordinarily effective means of rescue ventilation should mask ventilation and intubation fail, namely, the laryngeal mask airway.

Given the effectiveness of rescue ventilation devices, and alternative intubation methods, direct laryngoscopy efforts should generally not exceed three attempts and in many settings (prehospital) be limited to one or two attempts depending on practitioner's experience. Poor outcomes, that is, hypoxemia, regurgitation, aspiration, cardiac arrest, etc, have been associated with three or more laryngoscopy attempts in emergency situations.31

8.4.2 How Is Direct Laryngoscopy View Articulated and How Is This Clinically Relevant? Is Difficult Laryngoscopy Synonymous with Difficult Intubation?

Laryngeal exposure is only one step in the sequence of steps leading to successful intubation employing direct laryngoscopy. It is possible to have an excellent laryngeal view and be unable to intubate, as can occur with tracheal stenosis, for example. Conversely, an epiglottis-only view can sometimes be easily intubated on first attempt using a blind technique (ETI).

For laryngoscopy research and for documentation purposes, different systems have been created for reporting the extent of laryngeal view. The original system of grading laryngeal view, developed by Cormack/Lehane (C/L), categorizes laryngeal exposure into four grades: Grade 1—all of the vocal cords/glottic opening; Grade 2—only the posterior aspect of the glottis is in view (depending on external laryngeal pressure, part of the vocal cords and/or arytenoids may be in view); Grade 3—epiglottis-only; and Grade 4—no landmarks (not even epiglottis).32 Some researchers have subdivided the CL grading system to 3a and 3b. A 3a view is when the epiglottis is able to be lifted off the posterior hypopharynx, and 3b when it is touching the posterior wall (Figure 8-9).33 This difference in the position of the epiglottis is important as a posteriorly directed epiglottis creates a relatively more anterior glottic inlet that will not be easily accessed using an adjunct such as an ETI. A moderate degree of interobserver and intraobserver variability with this scoring system is known to exist.

A more statistically useful method of reporting laryngeal view is the Percentage of Glottic Opening Score, which is a numerical value from 0% to 100%.34,35 A full 100% POGO score would be a full view of the glottic opening from the anterior commissure of the vocal cords to the interarytenoid notch between the posterior cartilages. This system better distinguishes between CL Grades 1 and 2, which make up the vast majority of cases, but makes no distinction between CL 3 (including 3a vs 3b) and 4 (both would be POGO 0).

Adnet devised an Intubation Difficulty Scale, which incorporates laryngeal view as well as other aspects of intubation.36 They proposed an Intubation Difficulty Scale (IDS) score that is a function of seven parameters, resulting in a progressive, quantitative determination of intubation complexity. The score was intended to be used to compare difficulty of intubation under varying circumstances by isolating variables of interest. The seven parameters include:

• The number of attempts
• The number of operators
• The number of techniques (or devices)
• Cormack/Lehane view grade
• Lifting force
• Need for external laryngeal manipulation
• Position of the vocal cords (abducted/adducted)

There are numerous challenges when applying grading systems of laryngoscopy or intubation to patients. Fundamentally, the effectiveness of the procedure is also about the skill and ability of the practitioner. A Grade 3 CL view or difficult intubation employing Adnet's scoring system may be a Grade 1 view and an easy intubation in a different practitioner's hands.

Direct laryngoscopy and intubation is not an objective, easily graded diagnostic test, such as coronary angiography, for example. Not only does practitioner's technique impact dramatically on the result, but the performance is not routinely graded from the practitioner's perspective, and therefore, cannot be objectively assessed by other persons. With angiography, the images of dye filling the coronaries are not likely to be different when performed by a different operator, and the results can be reviewed by others. Direct laryngoscopy is dynamic, with the larynx transiently visualized for 5 to 15 seconds, and sighted by only one eye of the practitioner. Even if it was possible to capture what the practitioner was actually seeing during direct laryngoscopy and evaluate the performance, it still captures the procedural performance of only one practitioner and one event.

8.5.1 What Is Optimal Laryngoscopy and How Should the Practitioner Prepare for Direct Laryngoscopy?

The "Optimum laryngoscopic attempt" was characterized by Benumof as possessing six factors37:

• Most skilled individual
• Best paralysis
• Best position
• Best laryngeal manipulation
• Best laryngoscope blade type
• Best laryngoscope blade length

"Optimal laryngoscopy" refers to a combination of the proper equipment, a preplanned laryngoscopy strategy, and ideal patient conditions that collectively create optimal conditions for laryngeal exposure and first-pass intubation success.

Equipment must include suction (Yankauer), functioning oxygen delivery devices, and well-functioning laryngoscopes with optimal illumination. Tube delivery requires appropriately sized tubes, and stylets, along with a means of managing an epiglottis-only view (ETI and/or optical stylet). It is critical to have oral and nasal airways and an appropriately sized rescue extraglottic device (eg, LMA) immediately available, should intubation fail and rescue ventilation be required. Given the wide variety of alternative intubation devices, it is also appropriate to have an alternative device for intubation immediately available.

The importance of proper positioning, for both ventilation and direct laryngoscopy, cannot be overstated. Not only will ventilation be more effective in the ear-to-sternal notch position, but it will lengthen the time to desaturation in the patient who has been rendered apneic from their underlying condition or RSI (apnea time).38-40 Different methods of denitrogenation have been suggested to extend apnea time.41 These include having the cooperative patient take eight vital capacity breaths. Tidal volume breathing for 3 to 4 minutes using high-flow oxygen via a bag-mask device yields the best results. However, in some patient populations, such as the young pediatric patients, and patients with morbid obesity and critical illness, oxygen utilization is increased while reserves may be diminished.42 Desaturation will occur rapidly following apnea in these patients, requiring early mechanical ventilation, often before adequate intubation conditions (muscle relaxation) are achieved.43 Assisted ventilation in patients with low baseline saturations may be indicated during the preintubation phase. The risk of aspiration in carefully applied BMV is much less than the risk of desaturation in the critically ill patient. Denitrogenation will allow sufficient time for laryngoscopy and intubation in most patients without pulmonary pathology before desaturation occurs (longer apnea times).

While there has been debate about the indications for muscle relaxants outside of the operating room, there is no doubt that laryngoscopy is easier, more successful and done more quickly, and with fewer attempts when relaxants are used. The use of muscle relaxants offers two other very significant advantages. It eliminates the risk of active vomiting during laryngoscopy, and it permits the use of rescue ventilation devices (ie, LMA) should laryngoscopy fail. In emergency patients with full stomachs and short apnea times, these advantages may be important.

8.5.2 Is There a Role for Decompression of the Stomach Prior to Emergency Laryngoscopy, and How Should Nasogastric Tubes Already in Place Be Handled?

In patients with known bowel obstruction, significant GI bleeding, and perhaps in patients who have received prolonged assisted BMV (long prehospital course) it may be helpful to decompress the bowel as much as possible prior to muscle relaxation and laryngoscopy. These patients are at significant risk of regurgitation with the onset of muscle relaxation (see Section 5.5.4). Sellick recommended evacuating the stomach with a gastric tube and then removing the tube before induction of anesthesia.44 Others demonstrated no difference in the incidence of regurgitation with or without a nasogastric tube.45 It is the opinion of the authors that the nasogastric tubes should, if placed, remain in situ for the intubation.

8.6.1 What Is Epiglottoscopy and Why Is It Important When Performing Laryngoscopy?

"Epiglottoscopy" emphasizes the importance of visualizing the epiglottis prior to exposing the larynx and was one of Chevalier Jackson's basic rules of laryngoscopy.2 As an anatomic landmark the epiglottis has a unique importance to laryngoscopy for numerous reasons.

The epiglottis is the bridge between the starting anatomic landmark (the tongue) and the goal (the larynx). The relational anatomy, between the tongue, epiglottis, and larynx remains a constant despite person to person anatomic and pathologic variations. The epiglottis attaches to both the tongue and the larynx. It is connected to the base of the tongue at the vallecula. It is also the most superior aspect of the laryngeal inlet, a ring of structures that encircles the glottic opening. This ring is made up of the epiglottis, the paired aryepiglottic folds, the paired posterior cartilages, and the interarytenoid notch. Within the laryngeal inlet lies the glottic opening and vocal cords. The epiglottis is additionally a marker for the midline.

8.6.2 What Is "Epiglottis Camouflage"?

As stated earlier, the mucosal appearance of the epiglottis is identical to that of the posterior pharyngeal wall. In a supine position, with poor muscular tone, or after the administration of muscle relaxants, the jaw and base of tongue fall backward and the epiglottis lies against the posterior pharynx. Depending upon head and neck position, and the manner in which the laryngoscope is directed, it is easy to advance past the epiglottis as it is camouflaged against the pharynx. Overextension of the head, at the atlanto-occipital joint, moves the base of the tongue and epiglottis backward, making the situation worse, as do secretions, blood, and vomitus.

To overcome epiglottis camouflage and make the epiglottis edge distinctly visible, it is necessary to distract the jaw effectively and lift the base of the tongue. Keeping the face plane horizontal to the floor and elevating the head to ear-to-sternal notch position (if possible) permits optimal jaw distraction.

8.6.3 What Is the Best Method for Controlling the Tongue and How Does Tongue Control Integrate with Epiglottoscopy?

Effective control of the tongue is critical for straight blade use, and important as well with curved blades. Any amount of tongue positioned to the right of a narrow-lumen straight blade will make target visualization and tube delivery very difficult. The small flange height, especially of some Miller designs, prevents any ability to sweep the tongue, and practitioners should not attempt to do so. Proper position is achieved with straight blades by deliberately directing the blade to the right paraglossal space.23 When correctly positioned, the proximal portion of the blade is lateral to the right of the patient's right nostril and no tongue is present to the right of the blade. Insertion of the blade should occur through the right lateral mouth over the molar dentition. The distal blade may then be directed medially, although the proximal blade should never be brought back toward the midline upper incisors.

With a curved blade, the large reverse Z-shaped flange allows tongue sweeping. To avoid the thick chest or breasts, particularly in patients with a short neck, many practitioners prefer to insert the blade with the handle tilted sideways toward the right and insert the blade into the mouth at a slight right lateral position. A potential problem with this approach is that the epiglottis and the larynx are then approached off angle and depending upon the depth of insertion this can create landmark confusion. The aryepiglottic fold can be misinterpreted as the epiglottis edge, and if inserted too deeply the tip of the blade will pass under the posterior cartilages into the esophagus.

With the patient's face plane parallel to the ceiling, the author prefers to follow the curve of the blade down the curve of tongue, slightly to the right of midline, with early compression/lift of the tongue as necessary to visualize the epiglottis edge. In this first stage of laryngoscopy, only a gentle force is required to distract the jaw caudad, lifting the epiglottis edge off the posterior pharyngeal wall. The direction of the handle upon insertion and with initial jaw distraction is toward the patient's feet, and at a very shallow angle as the blade is advanced down the tongue (perhaps only approximately 20 degrees up from horizontal). Inexperienced users will commonly place the blade tip too far, before looking for landmarks. This is particularly common when using a longer blade (eg, #4 Macintosh blade). After the epiglottis has been recognized, and before the blade is engaged with greater force, the practitioner should check tongue position and move the blade rightward as necessary to effectively control the tongue. In practice, epiglottoscopy and tongue control happen simultaneously.

8.6.4 How Can Direct Laryngoscopy Be Made More Predictable and Not a Hit‐or-Miss Procedure?

From insertion of the blade until visualization of the larynx, there is a predictable, sequential exposure of landmarks that results from progressive advancement of the line-of-sight (LOS). As a laryngoscope blade is advanced over and down the surface of the tongue, into the pharynx, and then the hypopharynx, the LOS moves from the uvula, to the posterior pharynx, and then at the base of the tongue, to the epiglottis.

With the curved blade, the epiglottis is indirectly elevated, while with the straight blade the epiglottis is directly lifted. Once the epiglottis is visualized, the practitioner knows where the larynx will be located. Effective epiglottis control (either indirectly with a curved blade or directly with a straight blade) will then permit progressive exposure of laryngeal landmarks.

The structures of the larynx become visible from the most posterior to the most anterior. The most posterior laryngeal structures and the first visible under the epiglottis edge are the interarytenoid notch and the accompanying right and left arytenoids cartilages. Above the interarytenoid notch, and just medial to the arytenoid cartilages, is the posterior aspect of the glottic opening. Moving more anteriorly, the aryepiglottic folds are visible laterally, and the true and false vocal cords medially. Finally, most anterior and farthest within the laryngeal inlet, is the anterior commissure of the vocal cords.

8.6.5 What Are the Subtleties of Curved Blade Laryngoscopy, and What Is Bimanual Laryngoscopy?

The effectiveness of indirect epiglottis elevation hinges on proper placement of the blade tip in the vallecula as well as correctly directing force down the blade. Following epiglottoscopy, the tip of the blade needs to be fully advanced into the vallecula and the lifting force increased compared to what was needed for distracting the jaw and visualizing the epiglottis. The force direction is along the forearm and down the blade, in a manner that the practitioner's arm and forearm are extended away from the torso. The handle should not be tilted backwards, otherwise the tip of the blade will come out of the vallecula and there will be inadequate pressure on the underlying hyoepiglottic ligament. With the force directed down the blade (ie, the force vector approximately perpendicular to the practitioner), the tip of the blade can be effectively driven into the vallecula and resulting pressure on the hyoepiglottic ligament will cause the epiglottis to indirectly elevate (Figure 8-10).

If the tip of the blade is not fully seated into the vallecula engaging the hyoepiglottic ligament, no amount of lifting force will correctly elevate the epiglottis. A difference in blade tip placement of millimeters will affect the degree of epiglottic control. This is likely one of the primary reasons for skill-/experience-based variations in the laryngoscopic views. One way to seat the blade tip correctly is by performing bimanual laryngoscopy.46 The practitioner uses their free right hand to reach around to the anterior neck of the patient and apply external manipulation to the thyroid cartilage with a downward (backward, posterior) force.

The tip of the blade is like a key being inserted into the lock of the vallecula. Bimanual laryngoscopy serves to fully insert the key all the way into the lock, which only then will allow turning (elevating the epiglottis) and opening the larynx. In some cases, bimanual laryngoscopy may be best at the cricoid cartilage, or even the hyoid, although Benumof found that optimal manipulation was at the thyroid in almost 90% of cases.26 The practitioner need not be concerned about the exact position of their right hand. There is instantaneous visual feedback about the effectiveness of epiglottis elevation, and it is easy to move the right hand slightly up or down on the patient's neck to optimize the view.

Bimanual laryngoscopy improves laryngeal view in two ways. First, it changes the mechanics as described, correctly sitting the blade tip where it needs to be. Second, it helps to move the larynx downward (backward) into the practitioner's LOS. The mobility of the larynx and the ability of the practitioner to move it backward into view during the procedure was something known even to Czermark in the mid-19th century, when mirror laryngoscopy was first developed. Early wood block prints of Czermark performing mirror laryngoscopy show one hand on the patient's neck while his other hand holds the mirror within the mouth.2

A critical component of bimanual laryngoscopy is the direct practitioner connection between neck manipulation and the immediately observed effect on laryngeal view. Cricoid pressure (discussed later) and backward upward rightward pressure (BURP27) involve an assistant applying pressure to the neck. Given the subtlety of laryngoscopy, and that minor changes in blade tip position or force can significantly alter exposure and epiglottis control, bimanual laryngoscopy performed by the practitioner (referred by some as optimal external laryngeal manipulation, OELM) is the most effective means of optimizing laryngeal view.26 An assistant can be taught to maintain pressure at this location while the practitioner uses the right hand to pass the ETT.

The term "bimanual laryngoscopy" has also been used to describe a technique where the left hand manipulates the laryngoscope while the right hand is placed behind the occiput to manipulate the head and neck position to obtain the best view of the glottis.

8.6.6 How Is OLEM Different from Cricoid Pressure (the Sellick Maneuver)? Can Cricoid Pressure and OELM Be Used Together, or Should They (See Also Section 5.6)?

In 1961, Sellick described backward pressure on the cricoid ring by an assistant as a method of preventing passive regurgitation of stomach contents during elective anesthesia.44 It has become a standard part of emergency laryngoscopy and rapid sequence intubation/induction (RSI). It seems logical that pressure on the cricoid could occlude the esophagus and that this is advantageous in full stomach or aspiration-risk patients.

It is critical for airway practitioners to evaluate recent evidence regarding cricoid pressure and whether it should be a standard part of emergency laryngoscopy for two reasons. First, imaging of the neck with CT and MRI by Smith has established that the mechanics are not what they seem.47,48 Total occlusion of the esophagus does not occur in 91% of patients when cricoid pressure is applied because the esophagus is actually not midline, immediately behind the cricoid cartilage, but laterally displaced. However, Smith did find that the lumen of the esophagus was significantly compressed even if displaced laterally, and surmised that regurgitant fluid would be impeded by the maneuver, and recommended that there was no reason to suggest that traditional practice be abandoned.

The second reason why cricoid pressure should be examined critically is that the parameters of ventilation and positioning have changed dramatically from when Sellick conceived his technique. In Sellick's time, ventilation volumes averaged 10 to 15 mL·kg−1 and ventilation rates were 12 to 15 or more breaths per minute. Current practice is to use much smaller ventilation volumes, only 6 to 7 mL·kg−1, and higher ventilation rates to reduce the risk of exceeding esophageal opening pressure (25-30 cm H2O), yet again reducing the risk of gastric insufflation and regurgitation.

Sellick believed cricoid pressure would only work if the head and neck were placed in hyperextension in order to pin the esophagus between the cricoid and the vertebrae.44 He further advocated that the head be in a head down position. Should any regurgitation recur, the material could drain out and not into the lungs.44 This hyperextended head and neck position, and positioning the head down are antithetical to what we now know is optimal for effective ventilation and maximizing upper airway patency.

Laryngeal manipulation (BURP or bimanual laryngoscopy) should not be confused with cricoid pressure. Cricoid pressure is usually done by an assistant rather than the practitioner and it is not primarily intended to improve laryngeal exposure. It is also applied lower on the neck than laryngeal manipulation. If initiated upon induction (before blade insertion), cricoid pressure may prevent the blade tip from being correctly seated in the vallecula. Recent evidence has identified that the application of cricoid pressure may increase the incidence of a difficult emergency laryngoscopy (Grade 3 or 4 Cormack/Lehane view). A growing body of literature has highlighted the detrimental effects of cricoid pressure on laryngoscopy, mask-ventilation, and LMA placement although it has yet to demonstrate decreased gas exchange or increased intubation failure rates.49,50

In summary, it seems reasonable to continue with the practice of applying cricoid pressure (Sellick maneuver) at least until the evidence demonstrates that it is futile at preventing aspiration or leads to decreased gas exchange and increased intubation failure rates.

8.6.7 Apart from Paraglossal Placement, What Are the Specifics of Correctly Performing Straight Blade Laryngoscopy?

Much of the specifics of straight blade laryngoscopy have already been discussed, that is, paraglossal placement, and use of the extreme right corner of the mouth for blade positioning, tilting, and tube delivery. There is a critical aspect of straight blade laryngoscopy that needs to be addressed, however, and that is the direct lifting of the epiglottis.

After the epiglottis edge is identified, the handle must be tilted forward (eg, the tip backward, toward the posterior hypopharynx), the blade inserted slightly (approximately 1-2 cm), and the tip passed under the epiglottis. Once the epiglottis is trapped under the blade tip, the blade is rocked slightly backward (handle brought slightly more upright) and then the lifting force increased. Jackson described the lifting direction as suspending the patient's head with the flat section of the blade, at a point underneath the hyoid bone.2

Miller blades have an upturned distal tip that varies among manufacturers. This renders the distal blade tip invisible to the practitioner when viewed down the long axis of the blade. A potential problem with this design is that the practitioner does not know if the blade has been advanced far enough to trap the epiglottis until the blade is rocked backward; frequently the tip of the epiglottis is not trapped and the advancement and tilting maneuver needs to be repeated.

The Henderson blade is a novel straight blade design that has a deliberately visible distal tip. Underneath, within the barrel of the distal tip is a knurled edge that is easily seen when the practitioner looks down the blade (Figure 8-5). This allows the practitioner to place the tip under the epiglottis and know with certainty that the epiglottis is trapped.

OELM is helpful with straight blades because the posterior laryngeal pressure displaces the target into view.

8.6.8 in Addition to OELM, What Other Maneuvers Can Be Done during Laryngoscopy to Improve a Poor Laryngeal View?

Practitioners should understand and be ready to respond to poor laryngeal view within their first laryngoscopy attempt. There should be a specific planned approached to find the epiglottis and optimize blade tip position. In addition to OELM, and making sure the curved tip is driven fully into the vallecula, another technique for improving an epiglottis-only view is to dynamically lift the patient's head higher. This technique, which the author has called "head elevated laryngoscopy positioning" (HELP, and others have called "bimanual laryngoscopy"), was first described by Richard Johnston in 1909, and later adopted by Jackson and included in his subsequent textbooks.1,2,51 As already noted, head elevation permits greater jaw distraction because of its mechanically favorable effect on mouth opening. It enlarges the area beneath the base of the tongue and epiglottis improving visualization. According to Jackson, exaggerated head elevation also better aligned the blade axis with the axis of the upper trachea and larynx.

The practitioner can perform head elevation by using their right hand to lift the patient's occiput. Some practitioners have used their abdomen to lean forward and prop up and elevate the patient's head. Alternatively, an assistant can easily help by using two hands to lift the head from the patient's side. In the morbidly obese, dynamic lifting is often not feasible given the weight involved. A large ramp is needed extending from under the occiput, to the upper shoulders which then tapers to the mid-low back, in order to provide proper positioning (see Figure 18-2). An inflatable ramp has been designed for this purpose for airway management in the morbidly obese, called the "Rapid Airway Management Positioner."52 A noninflatable version is called the "Troop Pillow" (see Figure 49-2).

Regardless of which lifting technique is used, the patient's stretcher height must be kept low enough to permit head elevation and still provide a good perspective for the practitioner to look down the mouth into a patient whose face plane is parallel to the ceiling. For some practitioners, especially when dealing with larger patients, this may require a foot stool for the practitioner to be at proper height.

8.6.9 What Are the Most Common Errors of Direct Laryngoscopy by Novices?

The three most common errors that novice practitioners make during laryngoscopy include:

1. Placing the blade too deep before looking (not performing epiglottoscopy)

2. Entering the vallecula and lifting without engaging the hyoepiglottic ligament

3. Not using their right hand (bimanual laryngoscopy, OELM, BURP, HELP) to optimize the view

Novice practitioners move right past the epiglottis, insert the blade tip too deep, and then cannot recognize any laryngeal structures. They typically try to transfer their practice experience from an intubation trainer to an actual patient and find recognition of structures very difficult. This occurs because of unrecognized visual restrictions, epiglottis camouflage, and little understanding of the nuances of laryngeal anatomy. They also do not appreciate how minor manipulative adjustments of the blade tip affects laryngeal exposure, instead resorting to extra lifting effort. Their response to a poor laryngeal view is to move the blade in and out with large movements, leading to edema, tissue trauma, bleeding, and possibly perforation of the upper esophagus or hypopharynx. The best way to avoid landmark confusion is to be meticulous about epiglottoscopy.

Novice practitioners should carefully study video imaging of direct laryngoscopy prior to practicing on real patients paying particular attention to the nuances of anatomy and technique. The visual restrictions inherent to laryngoscopy make targeted feedback and supervision during the procedure impossible. With intensive video training, novice intubators can achieve a 90% success rate on their first 10 attempts, while with standard mannequin-only training initial success rates are low (50%).53 Following mannequin-only practice, a statistical modeling showed that the number of laryngoscopic intubations required to achieve a 90% success rate in anesthetized patients with a normal airway in an operating room environment was 47.54

8.6.10 Are There Specific Patients, Apart from Small Children, in Whom Curved Blades Perform Poorly or in Whom a Straight Blade Would Be the First Choice?

Patients who have lingual tonsillar hyperplasia have excess tissue at the base of the tongue and a small or nonexistent vallecula, making indirect epiglottis elevation very difficult. This is a rare condition, but can lead to unexpected failed laryngoscopy, since the base of tongue and epiglottis are not visible to oral examination during preprocedural assessment (see also Chapter 37). There are case reports of such patients being able to be intubated using a paraglossal straight blade technique.55 If the condition was known in advance, it would be prudent to avoid direct laryngoscopy altogether since it could prevent laryngeal exposure with a laryngoscope and also lead to very difficult mask and LMA ventilation.

Patients with large central dental gaps may be more easily intubated using a straight blade, since the large flange on the curved blade may lock into the gap creating a very restricted space for tube delivery. In such instances, ETI can be very helpful, or alternatively, a straight blade can be used with a paraglossal approach.

8.7.1 Tube Delivery as a Separate and Distinct Challenge from Laryngeal Exposure: Role for Stylets, Tube Introducers, and Optical Stylets

Polyvinyl chloride (PVC) ETTs have a gentle arcuate shape, as prescribed by American Society of Testing of Materials standards. The standard tube also has an asymmetric tip, with the bevel of the tube facing leftward when viewed from the practitioner's perspective ("Magill bevel"), down the long axis of the tube, as the tube is inserted into a patient.

The optical challenges of direct laryngoscopy have already been described. When there is favorable laryngeal exposure, tube delivery is rarely problematic. Conversely, when only a small portion of the glottic opening is visible, or even just the interarytenoid notch can be seen, tube delivery may obscure simultaneous visualization of the target.

All instruments designed to be passed into narrow body cavities have a narrow long-axis dimension and an upward distal turn. Instruments that adhere to this shape are alligator forceps, laryngeal mirrors, and ETI. The optical benefit of this shape is that the long straight section allows good maneuverability toward a target, while the upturned distal tip makes the tip of the device visible.

The large curvature of standard PVC ETTs (or those prepackaged with a matching arcuate-shaped stylet) is difficult to maneuver in the mouth and hypopharynx. They have a wide side-to-side dimension when viewed down the long axis, causing the tube to contact the sides of the mouth, tongue, and teeth. As efforts are made to direct the tip upward, for example, the midsection of the tube will contact the teeth when used with a stylet, causing bending of the midsection of the tube and stylet. The other problem with an arcuate-shaped tube (and stylet) is that minor rotational change will cause the distal tip to move substantially. When this occurs at the last moment of insertion toward the target, the midsection of the tube may visually block the target itself, leading to inadvertent and unseen passage of the tube into the esophagus.

A straight-to-cuff shaped tube and stylet has a narrow long axis and offers significant visual advantages than a tube alone, or a tube with an arcuate-shaped stylet.56,57 When viewed down the long axis it has a very narrow dimension. It can be passed into the mouth and easily maneuvered without obscuring the target as it advanced toward the target. The ideal method of inserting an ETT is to always pass the tube from beneath the line-of-sight, and bring the distal tube tip up from below, passing over the interarytenoid notch under direct vision without obscuring the target itself. Many practitioners prefer using a styletted tube for all tracheal intubations because of this maneuverability and visualization advantage. When the tube is first inserted in the extreme right corner of the mouth, the tube is placed visually behind the maxilla, and the distal tip is not even seen. By rocking the proximal tube backward, the distal tip moves posteriorly from behind the maxilla, up into the line-of-sight, and anteriorly until it is placed above the posterior landmarks of the larynx and into the trachea.

8.7.2 Where Exactly Should the Styletted Tube Be Bent, and What Is the Appropriate Angle to Use to Maximize Tip Visualization, But Not Mechanically Affect Insertion?

The historic approach to stylet shaping is to use a hockey stick. But this does not define the optimal bend point, or the proper angle. A more precise terminology is to use the term straight-to-cuff stylet shaping, followed by an angle not exceeding 35 degrees to the tube tip.58 This narrow long-axis shape is ideal for tube delivery toward the glottis, without blocking the line-of-sight. It still provides enough of a bend upward allowing the distal tube tip to be easily seen. The bend point should be at the proximal end of the cuff and the stylet should stop at the distal end of the cuff. The stylet can be dangerous if it protrudes beyond the tube tip. It can cause the tip to be too stiff even if it extends just to the tip of the tube. By stopping the stylet tip at the distal cuff, it provides an effective bend without stiffening the tip of the tube.

Angles beyond 35 degrees confer no visual advantage and hinder maneuverability within the mouth and hypopharynx. After the tip has passed into the trachea, bend angles above 35 degrees cause the tip of the tube to impact on the anterior tracheal rings.58 This phenomenon explains why it is possible to have a correctly sized tube between the vocal cords and be unable to pass the tube, even though the trachea itself is large enough to accept it.

8.7.3 What Should the Practitioner Do If the Tube Tip Catches in the Cricothyroid Space or on the Tracheal Rings after Insertion?

One option is to withdraw the stylet without withdrawing the tube itself. An assistant is necessary to do this since the practitioner will be holding the laryngoscope in their left hand and the tube in their right hand. By reducing the stiffness of the distal tube it may then be able to advance into the trachea. This maneuver however can easily result in dislodgement of the tube with resultant esophageal intubation on advancement.

Another option to rectify this mechanical hang-up on the anterior tracheal wall is to rotate the tube clockwise if resistance is felt. By turning the tube 90 degrees clockwise, the standard left-facing bevel of the ETT moves from facing leftward to facing upward. The leading edge of the tube rotates downward, away from the rings by this movement and it disengages.57

If time permits, Hung et al suggested the combination of softening of the ETT by immersing the ETT in warm saline solution, and reverse loading of the ETT onto the stylet may potentially overcome the problems with the hang up during intubation.59 With the reverse loading, the tip of the ETT is more likely to be directed down the trajectory of the trachea during the retraction of the stylet, making it easier to advance.

8.7.4 What Are the Options for an Epiglottis-Only View?

Assuming every effort has been made to maximize laryngeal view with the laryngoscope, there are several options for intubation. The first of these is to hug the undersurface of the epiglottis with the straight-to-cuff styletted tube, and being mindful of the tip orientation (keeping it upright), to insert the tube blindly. In general, blind insertion should be avoided.

An ETI can be used for intubation in epiglottis-only views. Newer disposable tracheal tube introducers are inexpensive. When compared with the use of a stylet in simulated Cormack/Lehane Grade 3 views, the success rates using this device is as high as 96% with the ETI and 66% using a stylet.60

In the true epiglottis-only view, the tip of the ETI is directed upward, hugging the undersurface of the epiglottis. Practitioners should be aware that minor rotational change will cause the tip to move lateral to the aryepiglottic fold (missing the larynx). The Eschmann tracheal introducer (ETI) is approximately 60 cm long, straight over its entire length, except for its distal end, which has a slight upward bend (Coude tip). The original Portex product (made of resin-covered fiberglass) has a bend angle of 38 degrees and this angle has been copied in the many disposable tracheal introducers now produced. After the tracheal introducer has passed into the trachea, the anterior tracheal rings may be felt (clicks) as the rounded tip passes over them. This occurs in 60% to 95% of cases, but it is practitioner and situation dependent, and also a function of the orientation of the distal tip. If the tip rotates downward after insertion, the tip will ride along the posterior membranous portion of the trachea and not pass over the rings (ie, no tactile feedback of tracheal placement). In the trachea, as the tip passes beyond the main stem bronchus, the narrowing diameter will cause it to stop between 30 and 35 cm. This distinct endpoint is more reliable in assessing tracheal placement. On reaching this endpoint, the tracheal introducer should be pulled back by 2 to 3 cm. When the tracheal introducer is placed into the esophagus, no rings are felt, and there should be no limit to advancement.

After tracheal introducer placement, the ETT is placed over the proximally stabilized tracheal introducer (by an assistant) and slid down (railroaded) its length into the mouth and ultimately the trachea. The laryngoscope should be maintained in the same position as was achieved during the initial laryngoscopy attempt. This promotes a long-axis slide of the ETT over the tracheal introducer. Without the laryngoscope, the tracheal introducer will bend in the pharynx and be surrounded by adjacent soft tissues which can cause difficulties with tube advancement. The beveled leading edge of the larger diameter ETT can holdup at the laryngeal inlet (right aryepiglottic fold, right arytenoid cartilage, or right vocal cord) as the tube is advanced over the tracheal introducer. This can be avoided by using a smaller ETT. This holdup is easily managed by turning (quarter turn) the ETT counterclockwise as it approaches the laryngeal inlet. This maneuver positions the bevel facing inferiorly, allowing uninhibited passage into the trachea.

It is important to note that there is major difference between the Cormack/Lehane Grade 3A and 3B—the latter being the situation where the epiglottis is visible but lies against the posterior hypopharyngeal wall. In this situation the tracheal introducer is not stiff enough to lift the epiglottis and it becomes more difficult to direct it into the glottis. The true incidence of this view is not known, and as stated earlier, may relate to improper blade tip placement deflecting the epiglottis posteriorly.

A more effective means for approaching the epiglottis-only view for practitioners who have acquired the skill is to use a malleable optical stylet.61 This permits target visualization either through an eyepiece or a monitor and the stylet tip can be advanced under indirect vision into the trachea. These devices require significant handling experience and recognition of fiberoptic landmarks and are addressed in Chapter 10.

Placement of a tracheal tube under direct vision using a laryngoscope remains one of the most important skills to master for all airway practitioners. Many types of laryngoscopes with curve and straight blades have been developed over the years with the objectives to improve visualization of the glottis and easy passage of the tracheal tube. While these devices are highly effective and safe, they all have limitations. To improve outcome and minimize the risk of complications, basic principles and techniques must be applied when performing a laryngoscopic intubation.