Macewan originally performed endotracheal intubation with his fingers.1 In 1913 Janeway used a speculum very similar to the laryngoscopes introduced by Miller and Macintosh in 1941 and 1942.2 And until recently, we’ve remained largely dependent on the line-of-sight technique exemplified by direct laryngoscopy (DL). It was proposed that “the sniffing position” aligns the axes of the mouth, pharynx, and trachea, yet the incisors, the tongue, the epiglottis, and occasionally the position of the larynx itself, often conspire against a clear view. Studies on conscious adults with normal airway features, in neutral, sniffing, and simple extension demonstrate that positioning alone does not align the axes3 and there was little difference between the sniffing position and simple extension in a large series of patients undergoing DL.4 If positioning does not align these axes, how do we accomplish intubation by DL? We apply force, displacing and compressing the tongue, mandible, and frequently the larynx itself. Yet even among adults with seemingly normal airways, it is not possible to view the larynx by direct means in approximately 6% to 10%.5–7 Despite attempts to do so, we frequently fail to identify patients in whom DL will prove difficult or worse.8 Studies suggest that when DL fails, all too frequently we try harder and more often,9 sometimes with adverse consequences.9–11
Instruments that are more or less anatomically shaped can overcome the anatomical barriers that may make DL difficult or impossible. Rigid and semirigid fiberoptic, optical, and video-laryngoscopes are designed specifically for this purpose.
Another significant limitation of DL is that the experience is difficult to share.12,13 Since only the laryngoscopist can visualize the procedure, this reduces the ability of an assistant to anticipate our needs, complicates the teaching and recording of laryngoscopy, limits clinical documentation and the possibilities for quality improvement as well as the conduct of airway research. Video-laryngoscopy circumvents many of these limitations but generally relies upon alternative devices. Visualizing the anatomy and the procedure of intubation can be achieved using a conventional laryngoscope. The Airway Cam®, developed by Dr. Richard Levitan, is a head-mounted camera which captures the laryngoscopist’s view through an eye-level pentaprism and conveys the image to a video monitor and/or a recording device.14,15 This device enables a student and mentor to simultaneously view the same object, capturing the image and playing it back at a pace and time conducive to and appropriate for teaching, documentation, and research. While these achievements are clearly worthwhile, this technology does not improve laryngeal exposure.
Flexible endoscopes have greatly expanded our ability to diagnose and manage problems in previously inaccessible body parts. These devices are versatile but complex. For tracheal intubation, flexible fiberoptic and video-endoscopes demand a different skill set than DL. Nonetheless, practitioners must master these devices, since they remain an essential tool in some situations. Their complexity and versatility also add to their cost and fragility. As well, blood, secretions, vomitus, or fogging may significantly interfere with visualization. Fiberoptic and video technology have been incorporated into flexible, semirigid, or rigid devices, designed specifically for tracheal intubation. Flexible fiberoptic and video-endoscopic intubation will be discussed elsewhere. Rigid and semirigid devices may be stylet-like (e.g., the Shikani Optical Stylet, Levitan FPS, Clarus Video System, Bonfils), channeled (e.g., WuScope, AWS, Airtraq, King Vision), or non-channeled and blade-like (e.g., C-MAC, GlideScope, McGrath, King Vision). All provide illumination and enable non-line-of-sight viewing. This is an evolving field, and the authors have endeavored to describe devices currently marketed in North America, supported by clinical evidence and in our opinions, worthy of the reader’s attention. It is likely that new devices will appear and disappear by the time of publication.
Evaluating the literature relating to the devices described herein is challenging. Many of the published reports involve practitioners with limited airway experience; more often they are unfamiliar with or poorly trained on the device being evaluated. The reader must be cautious when drawing conclusions based upon such studies. Comparisons too, must be treated with caution. It is unlikely that the laryngoscopist will be as familiar with a new device as he is with a standard tool such as a Macintosh laryngoscope. Using the conventional definition, a failed intubation is uncommon, and studies aimed at demonstrating superiority of one technique over another require a very large sample size. A selected population of patients known to be a difficult DL is more likely to give rise to meaningful data but may be difficult to justify ethically. Thus many of the studies have been done on a “standardized patient” (i.e., a manikin), a simulated difficult airway (e.g., with an applied cervical collar), in patients with features predictive of difficulty (which will undoubtedly include many false positives), or with surrogate outcomes (e.g., time-to-intubation, Cormack–Lehane (C-L) view, or number of attempts). Finally, the reader should critically assess whether the studies involve subjects that match the patients they encounter in their practice. The reader is invited to refer to a recent Cochrane Review regarding methodology and challenges in comparing evidence regarding the risks and benefits of video and DL for adult surgical patients.16
Compared with DL, few studies have been published on the anatomic predictors of difficulty in performing tracheal intubation using video-laryngoscopy (VL). Tremblay et al.17 prospectively studied 400 elective surgical patients. A detailed airway evaluation was done, followed by the induction of general anesthesia and pharmacologic muscle paralysis. DL was performed initially, and the C-L18 grade determined. Thereafter, another laryngoscopy using the first generation GlideScope video-laryngoscope (GVL, Verathon Inc., Bothell, WA) was performed, the view again graded and tracheal intubation performed. After multiple regression analysis, a C-L Grade 3 or 4 view at DL, poor mandibular protrusion (as reflected by a high upper lip bite test19), and a short sternothyroid distance were significantly correlated with both longer time-to-intubation and a higher number of intubation attempts.
Aziz et al.20 retrospectively evaluated the records of 2004 uses of the GVL in two institutions, most (81%) of which were performed on patients with preoperative predictors of difficult DL. Used as a primary or rescue device, failure to intubate occurred in 60 cases. Three anatomic predictors were significantly associated with GVL failure: altered neck anatomy (including mass, surgical scar, or radiation); decreased (<6 cm) thyromental distance; and reduced cervical motion. In this study, patient age, gender, body mass index (BMI), Mallampati classification, and reduced mouth opening (<3 cm) were not significantly correlated with difficult intubation using the GVL.
Siu et al.21 reported a prospective observational study of GVL intubations in 742 patients. The probability of successful first attempt tracheal intubation dropped from 81% in patients with normal airways to 73% in those with predicted or documented difficult DL.
Aziz and colleagues22 performed a secondary analysis of data obtained during a randomized controlled trial (RCT) comparing the GVL with the Storz C-MAC D-blade (Culver City, CA) for tracheal intubation of patients with predicted difficult DL. In this analysis, characteristics associated with greater risk for difficult VL were head and neck positioning in the “supine sniffing” versus “supine neutral” position, surgery type (otolaryngology and cardiac vs. general), intubation performed by an attending anesthesiologist versus an anesthesiology trainee, and small mouth opening.
Whether these anatomic predictors would also predict difficulty with video-laryngoscopes other than the GVL or C-MAC with D-blade is unknown.
Predictors of difficult tracheal intubation using VL are summarized in Table 11–1.
Predictors of Difficult Tracheal Intubation Using Indirect Video-Laryngoscopy
| Predicted21 or actual17,21 difficult direct laryngoscopy (e.g., Cormack–Lehane Grade 3 or 4 view) |
| High upper lip bite test (i.e., reduced mandibular protrusion)17 |
| Reduced mouth opening22 |
| Short sternothyroid distance17 |
| Altered neck anatomy (mass, surgical scar, radiation)20 |
| Decreased (<6 cm) thyromental distance20 |
| Reduced cervical motion20 |
| Positioning in sniffing position (vs. neutral)22 |
| Inexperience with technique20,22 |
| Surgery type (e.g., otolaryngology; cardiac)22 |
Interestingly, one nonanatomic predictor of failed GVL-facilitated intubation in the above-mentioned Aziz et al.20 study involving 2004 patients was intubation occurring in one of the two participating institutions. Over the study period, in the institution with the higher rate of failed intubation, practitioners had performed a median of only 6 intubations each, compared with a median of 19 at the second institution. This emphasizes the significance of a learning curve and maintenance of competence issues applicable to indirect VL.
Cortellazzi et al.23 studied the development of expertise in GlideScope VL in trainee anesthesia practitioners experienced with Macintosh blade (DL), but naïve to indirect VL. As expertise was the study endpoint, an “optimal” attempt was defined by successful first attempt intubation within 60 seconds, obtaining a C-L 1 laryngeal view and “no significant defect in technique.” Using these parameters, 76 intubations were required to predict a >90% probability of an optimal intubation. Another study of VL performed in the operating room environment also implies a significant learning curve: in a large observational cohort, Siu et al.21 reported that the first-attempt success rate increased from 69% for those with 0 to 9 previous uses of the GlideScope to 90% for those with 20 to 29 previous uses.
In the Emergency Department setting, Sakles et al.24 compared the first pass success rate of emergency medicine residents using the GVL in each of their 3 years of training with the corresponding rates for DL. For the GVL, success rates progressively improved, at 74.4%, 83.6% and 90% through training years 1, 2, and 3 years, respectively. In contrast, the corresponding figures for DL were 69.9%, 71.7%, and 72.9%, indicating no significant improvement beyond the first year. In the same institution, first pass success with the GVL used by attending staff physicians increased from 75.6% to 95.6% from the first to the last of 7 years studied.25
Baciarello et al.26 conducted a learning curve study of the Airtraq, comparing it to Macintosh DL skills acquisition in a group of 10 novice medical students. After a practice phase, clinical experience was observed in elective surgical patients. Over the course of 10 intubations with each device, seven students achieved a ≥90% success rate with the Airtraq, compared with only 1 for Macintosh DL. Differences in success rate were significant from the fourth attempt onward.
Learning curve studies are difficult to directly compare given varying study design, definitions of success, and participating practitioner experience. Notwithstanding, the available evidence indicates a significant learning curve for indirect VL in human subjects, particularly for the non-channeled blades. This implies that in planning the approach to a patient with predictors of difficult airway management, before relying on indirect VL for tracheal intubation of the patient after the induction of general anesthesia, the practitioner must be confident that he or she has ascended the learning curve for the technique.
In their study of 2,004 GVL intubations, Aziz et al.20 reported a 94% success rate (224 of 239) for GVL-facilitated tracheal intubations in the subset of patients where it was used after failed DL compared with their overall success rate of 98%.
Amathieu et al.27 reported on the efficacy of an airway algorithm applied to anesthetized, pharmacologically paralyzed patients. The algorithm called for use of the Airtraq after failed intubation by Macintosh DL with or without adjunctive use of a tracheal tube introducer (TTI). Of 12,225 patients included, 98% were successfully intubated with DL on its own; 207 of 236 were successfully intubated with DL/TTI; and of the remaining 29 patients, 27 were successfully intubated with the Airtraq. Malin and colleagues28 reported an 80% success rate of Airtraq-facilitated intubation in a series of 47 patients after failed intubation with a Macintosh blade. A TTI was used to facilitate the Airtraq intubation in a third of these cases. Earlier, Maharaj et al.29 had reported a case series of seven patients successfully intubated with the Airtraq after failed intubation using Macintosh laryngoscopy.
No studies were identified that specifically addressed the success of DL in facilitating tracheal intubation after failed intubation using VL. In Tremblay et al.’s17 study of predictors of difficult use of the GVL, 1 patient in the series of 400 could not be intubated with the GVL despite three attempts and a C-L Grade 1 view: DL allowed successful intubation on the first attempt. Aziz et al.20 witnessed failures in 60 of 2004 GVL attempted intubations: DL was used to successfully intubate 28 (47%) of these patients, while various other techniques were used for the remainder.
Direct and indirect laryngoscopy are different techniques, requiring different skills. The specific differences depend on the device. In general, with DL the objective is to optimize the glottis view and to the extent that this can be achieved, placement of the tracheal tube is relatively straightforward. When this can’t be achieved, head elevation, external laryngeal manipulation (ELM), or backward-upward-rightward-pressure (BURP) or use of a TTI might be attempted in an effort to bring the larynx into view or intubate blindly. With indirect techniques, a good laryngeal view does not assure tracheal tube placement. There are specific techniques that may increase the success of tracheal intubation. These are probably best discussed in relation to the specific devices. A general discussion may be found elsewhere.30
Optical stylets have a metal exterior containing fiberoptic bundles. When inserted within an endotracheal tube (ETT), the practitioner can view ETT advancement through a proximal eyepiece or a video monitor. The instruments vary in their external diameter, image resolution, source of illumination, and flexibility. At this point, the commercially available optical stylets with reasonable associated literature include the Bonfils Retromolar Intubation Fiberscope (Bonfils, Karl Storz Endoscopy, Culver City, CA); the Shikani Optical Stylet (SOS) and the Levitan FPS scope (both from Clarus Medical LLC, Minneapolis, MN), the Fiberoptic StyletScope (FSS, Nihon Kohden Corp., Tokyo, Japan), and the Video-Optical Intubation Stylet (VOIS, Acutronic Medical Systems AG, Baar, Switzerland). The Clarus Video System (Clarus Medical LLC, Minneapolis, MN) is the first semirigid optical stylet to be video-based.
Common to all optical stylets is a rigid or semirigid shaft and a proximal tube holder compatible with a 15-mm ETT connector. The tube holders can, on most devices, be adjusted on the stylet shaft, enabling appropriate positioning of the tip of the endoscope just within the distal tip of the ETT. Most optical stylets transmit light distally and the image proximally to an eyepiece through glass or plastic fibers of variable resolution. The distal viewing angle varies from 50 to 90 degrees. Light is generally powered from a battery source to enhance portability, although some scopes can be attached via a cable to a remote light source. None of the optical stylets have a hollow working channel. All of the optical stylets are susceptible to fogging and should be prepared with an antifogging solution or warmed prior to use.
The Bonfils is the only scope in this class of instrument that is nonmalleable. The shaft of the adult scope is 40 cm long and is bent 40 degrees anteriorly at its distal end. The adult version a 5.0-mm outer diameter (OD), accommodating an ETT with a 5.5 mm or greater internal diameter (ID) (Figure 11–1). Two smaller pediatric versions have ODs of 3.5 and 2.0 mm. A movable tube holder permits ETT fixation on the stylet shaft at a chosen location as well as oxygen insufflation down the ETT via an integrated luer-lock connector. Light is provided by cable from a remote light source, or by attachable battery-powered LED. The image is transferred by glass fiber (12,000 pixels), and the distal viewing angle is 90 degrees. A separate C-Cam video camera can be attached to the proximal viewing eyepiece for video image transfer to the Storz C-MAC system display screen.
The SOS is an example of a semi-malleable optical stylet (Figure 11–2). It is supplied with a bending tool and can accommodate an arc of up to 120 degrees. The stylet shaft is 27 cm long, and with an OD of 5.0 mm. It can accept ETTs >5.5-mm ID. A pediatric version is compatible with ETTs in the 2.5- to 5.5-mm ID range. ETT fixation on the stylet shaft is achieved by a movable “Tube Stop” adapter. The adapter accepts an attachment through which O2 can be delivered down the ETT. The distal viewing angle of the adult scope is 70 degrees. Glass fiberoptic bundles of 30,000 pixels are used to deliver the image to a fixed-focus, proximal eyepiece. Illumination is supplied by a standard green specification fiberoptic laryngoscope handle or a small battery-powered LED source. The eyepiece is compatible with proximally attached camera adapters, if desired. The company also supplies a passively flexible version of optical stylet called the Pocket Scope (Figure 11–3) designed for use with ETTs of 4-mm ID or larger, which can be used to confirm single- or double-lumen tube placement or patency.
The Levitan First Pass Success (FPS) Scope, developed by Dr. Richard Levitan, was derived from the Shikani SOS and intended as a low-cost fiberoptic stylet (Figure 11–4). The light source is supplied via an adapter from a standard Greenline handle or a dedicated portable LED. The shaft of the instrument is malleable through 90 degrees. Unlike other fiberoptic stylets, the 15.0-mm ETT connector adapter is in a fixed location on the handle. The ETT must be cut to an appropriate length to ensure that the stylet is within but close to the distal end of the ETT. A proximal connector permits oxygen insufflation down the ETT once attached. Levitan recommends shaping the Levitan FPS Scope “straight to cuff” (i.e., with an otherwise straight shaft bent anteriorly at an angle of no more than 25 to 35 degrees just proximal to the ETT cuff) and using it in conjunction with DL.31
The Fiberoptic StyletScope (FSS) is unique amongst the optical stylets in incorporating a lever adjacent to the proximal handle, enabling manipulation of the distal stylet angle during the tracheal tube placement. When depressed toward the handle, the distal stylet tip, with a loaded ETT, will flex anteriorly up to 75 degrees. The handle incorporates a holder that accepts the ETT’s 15-mm connector, and stylet length is adjustable to conform to ETT length. The light supply is built into the proximal battery handle, and is powered by two 1.5 V alkaline batteries.32 Fiberoptic imaging occurs via plastic bundles (3500 pixels), and the obtainable field of view is 50 degrees. With an OD of 6.0 mm, the FSS will accept a minimum ETT size of 7.0-mm ID.
The Clarus Video System (Trachway) is a video-based optical stylet with a handle-mounted 3-inch LCD screen (Figure 11–5) the viewing angle of which can be adjusted using a thumb control. A CMOS image sensor is located at the distal end of the stylet, which is detachable from the handle for cleaning and sterilization purposes. The rechargeable scope features two light sources: two white light LEDs, and one red LED, the latter being for anterior neck transillumination. The semi-malleable stylet shaft has an adjustable “Tube Stop” adapter to ensure the stylet is appropriately recessed with the ETT. Clarus Medical also markets the ClearSCOPE adapter to enable video capture using a smartphone from standard endoscope eyepieces, including those of the Shikani and Levitan FPS scopes (Figure 11–4).
The pediatric version of the SOS will accept a minimum tube size of 2.5-mm ID. An intermediate size of the Bonfils will accept a minimum tube size of 4.0-mm ID, while the smallest fiberoptic stylet in the Karl Storz family, named the Brambrink, will accept ETTs down to 2.5-mm ID.
Most of the optical stylets described above are similar in their structure, from which it follows that their function will also be similar. The following narrative describing the use of optical stylets, in general, can be applied to all.
An ETT should be preloaded on the optical stylet, and the proximal ETT connector stabilized within the tube holder on the stylet’s shaft. The tube holder and ETT are then positioned on the stylet’s shaft such that the scope tip is located just proximal to the ETT bevel. The tube holder is then fixed to the stylet shaft by tightening a locking screw. For semirigid devices, the desired degree of distal stylet angulation will depend on the technique of use: stand-alone use generally requires more angulation (e.g., 40 to 90 degrees), while fiberoptic stylet use as adjunct to DL should require a distal curvature of no more than 25 to 35 degrees.
Although optical stylets can also be used as an adjunct to DL, most practitioners opt for stand-alone use. A jaw lift, jaw thrust, tongue pull, or combination thereof33,34 should be performed to enlarge the pharyngeal space by elevating the tongue and epiglottis away from the posterior pharyngeal wall. The jaw thrust may also be beneficial by expanding the laryngeal aperture.35 Following suctioning, the stylet/tube assembly is inserted from the side of the mouth (i.e., advanced over or behind the molars) and slowly rotated upright and toward the midline during advancement,33 or alternatively, it can be inserted and advanced via a midline approach. For the midline approach, the stylet should generally be bent at a more acute angle, and during advancement, identification of the uvula and epiglottis will help maintain orientation to the midline position of the tip of the device. Once the tip of the stylet/tube assembly is at the laryngeal aperture, the ETT can be advanced off the stylet, through the glottis and into the trachea.
For optical stylet use as an adjunct to DL, the best laryngoscopic view is obtained. Faced with a poor view, for example, C-L Grade 3, an optical stylet loaded with an ETT is carefully placed just beneath the epiglottis, under direct vision. With the ETT tip under, but no more than 0.5 cm beyond the tip of the epiglottis, the practitioner then seeks a view through the stylet’s eyepiece (or on-screen): the vocal cords should be immediately visible, facilitating advancement of the ETT through the cords. If stand-alone optical stylet use has failed, using DL33,36,37 or VL38 in this fashion helps control the tongue and create space in the oropharynx for optical stylet manipulation. Concomitant use of DL with an optical stylet appears to be as effective as stand-alone use.39
Optical stylets have also been used in similar fashion to lighted stylets. Using only transillumination of the anterior neck to suggest successful tracheal access, secondary confirmation of correct placement can then follow by indirect visualization of the trachea through the eyepiece. This has been described with adult and pediatric optical stylets40 with a success rate that rivals the traditional visual advancement techniques.
Fiberoptic stylet use has been described to facilitate post-induction and awake41–43 intubations of adult and pediatric patients, with and without predicted difficult airway anatomy. Successful use has been reported with both single- and double-lumened tubes.44
Rudolph in 1996 reported on use of the Bonfils stylet in a series of 107 patients, of whom 18 presented C-L Grade 3 or 4 views at DL. Tracheal intubation was successful in 16 of 18 of the difficult cases with the Bonfils, including all four patients with DL-C-L Grade 4 views. Twenty-one percent of the total series required concomitant use of DL.36 Shikani,37 in his initial study of the SOS, looked at 120 patients, 74 of them children, including 7 patients with DL-C-L Grade 3 or 4 views. All patients in the series, including five awake patients, were successfully intubated with the scope, 88% on the first attempt. Five of the seven C-L Grade 3 and 4 patients required concomitant use of DL. Rudolph et al.45 described 116 patients with a C/L 3 or 4 laryngeal view or in whom more than 2 DL attempts were required. Patients were randomized to use of the Bonfils or a flexible bronchoscope (with sizes varying between 2.3 and 6 mm diameter). Concomitant use of DL, jaw thrust, an intubating oral airway, and size of ETT were not standardized. Total time-to-intubation was shorter with the Bonfils, with no difference in complications. Number of attempts was not separately reported. Later, Bein et al. compared the use of the Bonfils with the LMA-Fastrach™ in 80 patients with predictors of difficult DL. Thirty-nine of 40 patients randomized to Bonfils use were intubated on the first attempt with a median time of 40 seconds, in contrast to a 28/40 first-attempt success rate for the LMA-Fastrach.34 A second study evaluated the Bonfils use after failed DL. In 25 patients recruited following two failed DL attempts, 88% were successfully intubated with the Bonfils at the first attempt, and all but one (96%) by the second attempt, with a median time of 47.5 seconds.34 In Falcetta’s learning curve study involving 216 patients using the Bonfils, 15 patients presented a C-L Grade 3 or 4 view during prior DL. All were intubated successfully with stand-alone use of the Bonfils in a median time comparable to patients who presented a C-L Grade 1 or 2 by DL.46 Finally, in a similar study, Kim and group47 randomized 40 elective adult surgical patients presenting DL-C-L Grade 3 view to use of the Bonfils or a 3.8-mm bronchoscope. Both devices were used with concomitant DL. First-attempt success rate was comparable at about 50%, while times to ultimate success was shorter in the Bonfils group. Two cases failed with the Bonfils and succeeded with the flexible bronchoscope.
Case reports document successful use of the Bonfils in patients with limited mouth opening (7 and 15 mm).48
How Effective Are Optical Stylets for the Awake Tracheal Intubation of the Patient with Anticipated Difficult Airway Management?
Several series and reports have documented the successful use of the Bonfils optical stylet for awake tracheal intubation, for a variety of indications, and in some cases after the failure of flexible bronchoscopic intubation.41,49–51 The Clarus Video System was described in one case report to facilitate awake intubation with a double-lumen tube in a topically anesthetized patient with a large epiglottic cyst,52 and for awake intubation of a patient immobilized in a halo jacket.53
Greenland and coworkers compared the Levitan FPS scope with the single-use Portex tracheal introducer in a randomized cross-over study of 34 adult patients. They found equal success and a shorter time-to-intubation with the tracheal introducer under conditions where only a C-L Grade 3A view was deliberately obtained during DL.54
The Bonfils stylet was compared with Macintosh blade DL in a population of elective surgical patients in whom difficulty was simulated by application of a cervical collar. Tube placement was successful in 81.6% of patients randomized to the Bonfils stylet versus 39.5% of the Macintosh DL patients.55 More recently, in a study of 120 elective surgical patients wearing cervical collars randomized to use of left molar laryngoscopy with adjunctive use of a TTI or intubation with the Bonfils, the Bonfils resulted in a significantly shorter total time-to-intubation, with a comparable overall success rate.56 Another study performed under similar conditions compared the GlideScope with the SOS. Comparable overall and first-attempt success rates and time-to-intubation occurred.57
What Is the Role of the Optical Stylet for Intubation of the Patient with Known or Possible Cervical Spine Instability?
Two studies have compared Bonfils-aided with Macintosh blade (attempted full view exposure of cords) DL, one using noncontinuous radiographs58 and the other using external markers as a surrogate of cervical spine movement.59 Subjects in the two studies started with the head and neck in a neutral position, but had no application of in-line cervical immobilization. Both studies documented significantly less upper cervical spine movement with the Bonfils. Using the SOS with in-line cervical immobilization and continuous fluoroscopy, another study similarly concluded that less movement occurred with the SOS than with Macintosh blade DL.60 The clinical significance of these studies is unknown.
Successful use of optical stylets for double-lumen tube placement has been described in case reports with both the Bonfils44,61 and the OptiScope (Pacific Medical, Seoul, South Korea), a modified version of the Trachway video-based optical stylet. This device, also semi-malleable, is 40.5 cm long and has an OD of 5 mm, meaning that it can be used in 35-Fr or larger double-lumen tubes.62 Yang and colleagues62 conducted a study of 400 patients randomized to 35- and 37-Fr double-lumen tube insertion with Macintosh blade DL or stand-alone use of the OptiScope. OptiScope-facilitated intubation was faster, and succeeded on the first attempt significantly more often than Macintosh-blade facilitated intubation. Overall success rate was similar, although the incidence of mucosal or dental injury was significantly less with OptiScope use.
The Clarus Video System/Trachway was used in a study of 60 patients,63 similarly randomized to Macintosh blade DL or the Trachway for placement of a DLT. Intubation occurred on the first attempt in all 60 patients, but more quickly (mean of 48 vs. 28 seconds) with the Trachway, and with less postoperative hoarseness on the first 4 days of observation for such complications.
Semi-malleable optical stylets have been described for nasotracheal intubations. Hsu and colleagues studied 100 patients, allocating 50 to use of the Trachway stylet through the nose, or nasotracheal intubation facilitated by oral Macintosh DL. All Trachway intubations succeeded on the first attempt in less time than those facilitated by DL, with less need for corrective maneuvers during the procedure and comparable complications such as bleeding.64 Lee et al.65 studied 80 patients with limited mouth opening and an average BMI <25 kg·m−2, randomizing them to nasotracheal intubation with the Trachway or a flexible bronchoscope. Intubation with the Trachway occurred significantly faster and with less difficulty on a modified intubation difficulty scale. Success rates within two attempts were comparable, as were bleeding complications.
Case reports have been published documenting successful tracheal intubation using optical stylets in pediatric patients with actual or predicted difficulty due to Pierre Robin sequence,66,67 Hurler syndrome,68 Goldenhar syndrome,66 Treacher Collins syndrome,66 restricted mouth opening with popliteal pterygium syndrome,69 and small for gestational age conditions.70 In all of these cases, either a Brambrink or Shikani stylet was used as a stand-alone technique. However, unlike the foregoing successes, Bein published a series of 55 uses of the Bonfils and Brambrink optical stylet in elective pediatric surgery patients without predictors of difficult airway anatomy. Although performed by an investigator experienced in adult use of the Bonfils, this study reported a relatively poor success rate with the device, with many of the failures due to secretions. In the series, the tracheas of only 40 of 55 (73%) patients were intubated on the first attempt, and after three attempts there was a failure rate of 9%.71 Houston et al.72 randomized 50 healthy children to intubation with the Bonfils or DL with prior laryngoscopy with the alternate device: although the Bonfils resulted in more Grade 1 views, four patients required two attempts, and two failed after two attempts; compared with two requiring two attempts with DL and no failures with DL.
More recently, Kaufmann et al.73 compared the Bonfils with the GlideScope Cobalt AVL video-laryngoscope in 100 children. Visualization of the larynx was better with the Bonfils, and time needed for intubation was significantly less. All cases were successfully intubated with both devices. Subsequently, the same group compared use of the Bonfils with the flexible bronchoscope for intubation of 26 pediatric patients with anticipated or actual difficult airway anatomy.74 All 26 patients were intubated successfully on the first attempt with either device, although the time required, image quality, and ease of the procedure were significantly improved with the Bonfils. Successful use of the semi-malleable SOS has been described to facilitate intubation through an air-Q extraglottic device in seven pediatric patients.75
One interesting case report documents successful use of the Bonfils “in parallel” with an in situ extraglottic device (air-Q): the loaded Bonfils was successfully advanced via the retromolar approach around the right side of the cuff of the air-Q, to and through the glottic opening.76
Using time to successful tracheal intubation as a marker for proficiency, published learning curve data on the Bonfils fiberoptic stylet suggest that 20 to 25 uses are needed to achieve competence.33,42,46 Other published reports of experience with optical stylets detail most of the failures at the beginning of their respective series (i.e., within the first 10 uses).37 In one series, the most commonly encountered preventable difficulties included secretions, fogging and difficulty getting under the epiglottis. These problems may be circumvented with anti-fogging maneuvers, a jaw thrust or concomitant laryngoscopy.
To date, most complications reported in the literature due to optical stylets have been limited to failures to intubate71: airway trauma has been reported only infrequently.33 One case report has appeared documenting extensive facial and neck edema after an intubation attempt during which O2 was insufflated at 10 L·min−1 via the tube holder adapter on a Bonfils stylet.77 Otherwise, failure to intubate has sometimes resulted from a view being obscured by fog or secretions, often a preventable complication.
As a class, optical stylets are portable, and, relative to flexible bronchoscopes, less expensive and more robust. Their rigidity may make them easier to navigate to the laryngeal inlet than flexible devices. As outlined above, published studies and case series suggest that at least in the hands of experienced practitioners, optical stylets enable a high rate of successful tracheal intubation in patients presenting predicted or actual difficult DL. Compared to DL with the Macintosh blade, tracheal intubation with both the Bonfils78,79 and the StyletScope80,81 have been associated with a lower incidence of adverse hemodynamic responses, although in another study comparing DL by a left molar approach to use of the Bonfils, hemodynamic responses were no different.56 In a study comparing the Bonfils (using a midline approach) with tracheal intubation using a flexible bronchoscope in anesthetized patients, a comparable hemodynamic response was noted.82
Prior antifogging preparation and suctioning are recommended for optical stylet use. Some optical stylets require the ETT be cut to a specific length. During advancement toward the glottic opening, orientation within the upper airway can be difficult unless soft tissues are well controlled with a jaw lift or by concomitant use of a direct- or video-laryngoscope. It follows that poor jaw protrusion, as well as significant blood or secretions in the airway may create difficulties. It is also probable that intubation using optical stylets will be more successful in the hands of practitioners already experienced in the use of flexible bronchoscopes. Non-malleable versions of optical stylet (i.e., the Bonfils) are not suitable for nasotracheal intubation.
Three devices typified this class of laryngoscopes: the WuScope, the UpsherScope, and the Bullard Laryngoscopes. They have several things in common—a rigid, anatomically shaped blade, a fiberoptic bundle, a viewing port, and the decision by their respective manufacturers to discontinue the products. They will be discussed briefly because of their relationship to VL, the fact that they still have their adherents and are referred to in the literature. The interested reader can find additional details about these devices elsewhere.83,84 These devices lacked angulation controllers making them less versatile and less expensive but easier to use. The fiberoptic bundles were protected within the blade and thus less vulnerable to damage. The rigid fiberoptic laryngoscope is inserted into the mouth and positioned around the base of the tongue, providing the practitioner with an excellent glottic view. Unlike the flexible fiberoptic device, these laryngoscopes remained above the larynx allowing the laryngoscopist to observe the insertion and advancement of the tracheal tube. This differs fundamentally from flexible endoscopes. Flexible endoscopes are generally advanced well into the trachea, thereafter serving as an introducer over which the tracheal tube is blindly advanced. This is not intended to diminish the importance or versatility of flexible endoscopy. It is meant to draw attention to the reality that tracheal tube advancement is unobserved from its insertion until it approaches the distal trachea.
The optical eyepiece of a rigid fiberoptic laryngoscope can be coupled with a clinical video camera and viewed on a separate monitor. The Bullard Laryngoscope (Olympus, Norwalk, OH) was introduced nearly three decades ago. Its distinguishing feature is a very slim, 6-mm profile enabling its use in patients with a very limited mouth opening. The UpsherScope (Mercury Medical, Clearwater, FL) consists of a J-shaped stainless steel blade with a channel along its right side through which a preloaded ETT was advanced. The WuScope (Achi Corporation, Freemont, CA) consists of two semicircular blades that enclosed a fiberoptic nasopharyngoscope and the ETT, each within a dedicated slot. After intubation was achieved, the WuScope blades were uncoupled and individually withdrawn.
While some practitioners were frustrated by fogging, secretions, and the need to elevate the epiglottis, a greater obstacle to clinical and marketing success was the relatively flat learning curve and limited number of experienced practitioners to serve as mentors. Practitioners had presumably found the transition to VL easier because of the similarity of VL to conventional Macintosh blades and the market for the rigid fiberoptic laryngoscopes all but disappeared.
The Bullard Laryngoscope has been used in patients with simulated difficult airways, microstomia, micrognathia, Pierre Robin syndrome, cervical spine instability or restriction, and lingual tonsillar hyperplasia.85–92 Neither the UpsherScope nor its successor, the UpsherScope Ultra™ were widely used. Numerous case reports and small series describe the use of the WuScope in challenging settings.93–96
Other rigid fiberoptic devices have come and gone. None of these enjoyed popularity in North America and there are limited clinical studies demonstrating their effectiveness. Examples of these include the EVO II (Viewmax or Truview, Truphatek, Israel)97,98 and the Angulated Intubation Video-Laryngoscope (AVIL, Acutronic, Switzerland).99
Earlier rigid fiberoptic laryngoscopes conveyed their image along a bundle of glass fibers to an eyepiece. If the eyepiece was connected to a video camera, the benefits of video-laryngoscopy were achieved, albeit with somewhat greater complexity. The optical stylets and rigid fiberoptic laryngoscopes (e.g., the Bullard Laryngoscope, UpsherScope, and WuScope) as well as the Truview-EVO can all be connected to a video camera in this way. As previously mentioned, VL can also be achieved using a conventional direct laryngoscope and an Airway Cam. More recent video-laryngoscopes incorporate a video camera, or more precisely a video chip (CMOS or CCD) into the stylet or blade. They use light-emitting diodes (LEDs) for illumination and a liquid crystal display (LCD) for monitoring the image. There are several ways of classifying these devices: single-use versus reusable blades; traditional Macintosh-style versus more angulated blades; and channeled versus non-channeled blades. Each category has advantages and disadvantages. For example, single-use products permit a faster turn-over between uses since reprocessing is not required. Other considerations relating to the single-use versus reusable products include the environmental impact of packaging, disposal and potentially hazardous reprocessing, the cost-per-use, the design, strength, and performance of single-use versus reusable devices. In some jurisdictions, the practitioner may have no choice in that single-use products are mandated in the interests of infection control.
Although indirect VL blades are effective in obtaining a view of the larynx, on occasion, ETT passage may be problematic. To help address this issue, a number of VL blades incorporate a channel designed to help guide the ETT through the oropharynx to and beyond the larynx. These include the King Vision video-laryngoscope (channeled blade version) (Ambu Inc., Columbia, MD), the Pentax Airway Scope (Hoya Corporation, Tokyo), the Airtraq (Prodol Meditec SA, Guecho, Spain), the Venner AP Advance (Venner Medical, Singapore), and the VividTrac® (Vivid Medical Inc., Palo Alto, CA) Most channeled blades are wider or thicker than their non-channeled counterparts. This may be a limitation, particularly for patients with a small mouth or interincisor distance. A technical comparison of several of the devices described below may be found elsewhere.100
The Airtraq laryngoscope is a J-shaped, channeled-blade indirect laryngoscope that can be used either with its standard integrated optical viewer or with attachable video-enabling technology. A series of mirrors optically delivers an indirect image to a proximal eyepiece. The Airtraq SP is entirely a single-use device (Figure 11–6), available in a number of sizes (Table 11–2). The vertical profile of the regular (size 3) Airtraq is 17 mm. Illumination is supplied from a distal LED bulb, and a heating element heats up the distal viewing lens as an antifogging measure. The Airtraq Avant features a reusable, rechargeable optical unit that slides into a single-use blade (Figure 11–7). The optical unit is recharged in a docking station between uses, and is discarded after 50 uses. Both versions of the Airtraq can be video-enabled in a few ways. First, there is a universal smartphone adapter, compatible with most smartphones. This is used in conjunction with an app (“Airtraq Mobile”) that allows videoscopic transfer of the Airtraq’s optical image onto the smartphone’s screen in real time (Figure 11–8). Second, an attachable WiFi camera is available that will enable wireless transfer of the image to a mobile phone or personal computer.
Blade Name, Color-Coding, Vertical Profile and Recommended Tube Sizes for Various Channeled Video- or Video-Enabled Indirect Laryngoscopes
| Blade Name/Size | Color Coding | Vertical Profile, mm | Maximum Tube Size, ID, mm |
|---|---|---|---|
| Airtraq SP | |||
| Regular, size 3 | Blue | 16 | 7.0–8.5 |
| Small, size 2 | Green | 15 | 6.0–7.5 |
| Pediatric, size 1 | Purple | 12 | 4.0–5.5 |
| Infant, size 0 | Gray | 11 | 2.5–3.5 |
| Nasotracheal (no channel) | Orange | 15 | n/a |
| Double lumen | Yellow | 18 | 28–41 Fr |
| Airtraq Avant | |||
| Regular, size 3 | Blue | 17 | 7.0–8.5 |
| Small, size 2 | Green | 16 | 6.0–7.5 |
| King Vision, and King Vision aBlade, Channeled Blades | |||
| Adult | n/a | 18 | 6.0–8.0 |
| Pediatric | n/a | ||
| Pentax Airway Scope | |||
| MITL-SL Standard | Clear | 8.5–11.0 outer diameter | |
| MITL-TL Thinner | Green | 7.5–10 outer diameter | |
| MITL-PL Pediatric | Pink | 5.5–7.6 outer diameter (without cuff) | |
| ITL-NL Neonate | Blue | <5.0 outer diameter (without cuff) | |
| Venner APA | |||
| DAB (channeled) | n/a | ||
| VividTrac | |||
| Adult VT-A100 | n/a | 6.0–8.5 | |
| Pediatric VT-P100 | n/a | 4.0–6.0 | |
For use, an appropriately sized Airtraq is lubricated within the channel, and turned on.
Once turned on, the distal heating element begins to warm up the lens, indicated by flashing of the LED light until the desired temperature has been attained (30 to 60 seconds).
The ETT is loaded within but not beyond the end of the channel.
Airtraq insertion is over and following the midline of the tongue, with the ultimate goal of blade placement in the vallecula.
Appropriate blade positioning is indicated by obtaining a view of the glottis that is centered in the viewfinder, with arytenoid cartilages well below the horizontal midline of the display.
It will sometimes be necessary to retract the blade from the glottis, and to lift the device somewhat to obtain the optimal view.
ETT delivery follows by its advancement through the channel: gentle counterclockwise twisting will sometimes facilitate ETT passage through the cords.
Once tracheal intubation is complete, the tube is stabilized, whereupon the Airtraq is rotated forward out of the patient, while the ETT is separated laterally from the delivery channel.
The Pentax Airway Scope is a battery-powered indirect video-laryngoscope. A proximal handle incorporates a 2.4-inch video display and batteries, ending distally in a cable that houses an LED light and CMOS sensor (Figure 11–9). The cable drops into a single-use blade (“Pblade”), available in various sizes (Table 11–2) that also has separate channels for an ETT and a suction catheter. A unique feature of this video-laryngoscope is an aiming reticle (i.e., “cross-hairs”) that can optionally be activated on the video display, designed to help line up the scope with the glottic opening to optimize ease of ETT passage. The first-generation AWS-S100 stem has now been upgraded to the lighter AWS-S200, and is water-resistant.
For use, the AWS is prepared by attaching the appropriately sized blade to the display stem.
An ETT is loaded into the well-lubricated channel, with its tip adjacent to the tip of the camera cable.
The loaded device is advanced over the tongue in the midline
As the blade is advanced, and unique to this video-laryngoscope, one should seek to directly lift the epiglottis, rather than placing the blade in the vallecula. This relates to the fact that once advanced out of the channel, the ETT tends to hug the inferior surface of the Pblade; thus, were the blade to be placed above the epiglottis, the advancing ETT could impact and downfold the epiglottis, thus impeding further advancement.101,102 There is some suggestion that if the epiglottis cannot be directly elevated and the blade must instead be located in the vallecula, use of a Parker Flex-Tip tube will increase the intubation success rate, compared with a regular ETT.103
The ETT is advanced to and through the glottis. If using the aiming reticle on the video display, it should be centered over the glottic opening.
After successful tracheal intubation, the device is rotated forward out of the patient, while the securely held ETT is separated laterally from the channel.
The King Vision video-laryngoscope features a reusable, portable, battery-operated display with a 6.1-cm/2.4-inch organic LED (OLED) screen (Figure 11–10). In the original version of the King Vision, the video display attaches directly to a single-use, J-shaped blade. The blade incorporates a single-use video chip, and is available in standard (i.e., no channel) and channeled versions. A more recent variation is the King Vision aBlade video-laryngoscope. This version features an additional component: a video adapter that includes the LED light and CMOS camera in its distal tip. The video adapter couples proximally with the standard video display, and is placed within a single use blade (Figure 11–11). Clear, single-use, antifog coated aBlades are also available in standard and channeled versions (Table 11–2).
For use of the channeled King Vision blade, the channel should be pre-lubricated with a water-soluble lubricant.
The ETT can be preloaded in the channel with its distal tip aligned with the end of the channel. Alternatively, the ETT can be advanced through the channel once the blade has been positioned in the patient.
After suctioning, midline blade insertion into the patient should occur by advancing it over the tongue.
Watching for the epiglottis, the blade should generally be directed into the vallecula, although a direct lift can be performed in case of a long, “floppy” epiglottis.
As with most video-laryngoscopes, it is important to not position the blade too close to the glottis.
The ETT is then advanced via the channel to and through the glottic opening.
Adjustments to the blade’s position to accomplish successful ETT passage may include withdrawal, lifting, and slight leftward orientation (this orientation aims the leading edge of the ETT’s bevel away from right-sided laryngeal structures).
Sometimes, as the ETT is advanced through the glottis, a 90-degree counterclockwise rotation of the ETT within the channel will also help avoid ETT impingement on right-sided laryngeal structures.
After successful tracheal intubation, while stabilizing and holding the ETT, the King Vision is rotated forward out of the patient. As the blade exits the patient, the tube is easily separated from the channel laterally, to its right.
The Venner APA™ is a video-laryngoscope with a variety of single-use blade options (Figure 11–12). One of these includes a channeled version. Its components include: the video viewer, an 86-mm/3.5 inch screen; the camera module, the handle, and the single-use blade. Single-use blade options include Macintosh 3 and 4 blades and the hyper-angulated difficult airway blade in channeled (DAB) and non-channeled (U-DAB) versions. The camera module incorporates a high-intensity LED light source and CMOS camera sensor. The battery-powered device is rechargeable. Single-use blades are antifog coated.
For use, the Venner APA is prepared by attaching the video viewer to the top of the APA handle by pressing firmly down into place. The camera module is attached to the handle, and once placed in the “on” position, will illuminate distally. The chosen blade slides over the camera module until it clicks into place.
The channeled DAB blade should be lubricated before use.
The blade should be introduced in a midline position.
In advancing the ETT through the channel to and through the larynx, no introducer or stylet should be needed.
The VividTrac® (Vivid Medical Inc., Palo Alto, CA) is a single-use, channeled indirect video-laryngoscope. Available in one adult (VT-A100) and one pediatric (VT-P100) size, the J-shaped device connects via USB cable to a variety of display options, such as a tablet. The laryngoscope features an integrated tube delivery channel that in the adult version will accommodate tubes sized from 6.0- to 8.5-mm ID and in the pediatric version, from 4.0- to 6.0-mm ID. The laryngoscope derives its power from the tablet or computer to which the USB cable is connected, and features an automatically antifogging camera distally.
For use, an ETT is preloaded into the delivery channel, advanced until the tube’s tip is just visible in the right-hand side of the video image.
Midline insertion follows, with the blade tip preferentially positioned above the epiglottis, and the glottis centered on the display.
Tube passage follows by its advancement via the channel through the glottis and down the trachea.
Corrective maneuvers to prevent or overcome tube impingement may include withdrawal, backwards angulation, or slight left-right, or up-down adjustments to help center the glottis in the video display.
Slight counterclockwise rotation of the ETT within the channel during advancement may also be beneficial.
Substantial literature appears on the Airtraq. These studies are consistent in the finding of an improved laryngeal view compared to Macintosh DL but sometimes disagree in their results with respect to first attempt intubation success, time-to-intubation, and results in expert versus novice hands. In their systematic review and meta-analysis of RCTs comparing the Airtraq with Macintosh blade DL, Lu et al. found that the Airtraq reduced intubation time in both experienced and novice hands, but increased first-attempt success only for novices. Esophageal intubation was reduced, but other complications were no different. Intubation Difficulty Scale104 scores when reported were reduced by the Airtraq, and the percentage of glottic opening (POGO)105 was improved.106 In another systematic review and meta-analysis, RCTs of patients undergoing cervical spine immobilization were pooled to compare multiple indirect VL devices with Macintosh blade DL. The Airtraq alone was associated with all of improved glottic visualization and a significant reduction in the risk of first attempt intubation failure, time-to-intubation, and oropharyngeal complications. Other devices, including the AirwayScope, GlideScope, C-MAC (blade type not stated), and McGrath (type and blade not stated) were associated only with improved glottic visualization.107
Related posts:
Direct Laryngoscopy
What Is Unique About Airway Management in the Pre-Hospital Setting?
Airway Management in a Patient with Angioedema
Lung Separation in the Patient with a Difficult Airway
Airway Management of a Patient with a Difficult Airway Requiring Microlaryngoscopy, Tracheoscopy, and Pharyngoesophageal Dilation
Cannot Intubate and Cannot Oxygenate in an Infant After Induction of Anesthesia
Full access? Get Clinical Tree
