Videolaryngoscopy

Abstract

The approach to airway management has undergone a dramatic transformation since the advent of videolaryngoscopy (VL). Videolaryngoscopes have quickly gained popularity as an intubation device in a variety of clinical scenarios and settings, as well as in the hands of airway experts and non-experts. Their indirect view of upper airway improves glottic visualization, including in suspected or encountered difficult intubation. Yet, more studies are needed to determine whether VL actually improves endotracheal intubation (ETI) success rates, intubation times, and first attempt success rates; and thereby a potential replacement to traditional direct laryngoscopy. Furthermore, advances in technology have heralded a wide array of models each with their own strengths, weaknesses, and optimal applications. Such limitations need to be better understood and alternative strategies should be available. Thus, the role of VL continues to evolve. Though it is clear VL expands the armamentarium not only for anesthesiologists, but all healthcare providers potentially involved in airway management.

INTRODUCTION

Videolaryngoscopy (VL) utilizes video camera technology to visualize airway structures and facilitate endotracheal intubation (ETI). Given the advances in video technology, more reliable, powerful, and less expensive videolaryngoscopes are emerging on the market with increasing availability.[1] This emergence has been ushered in by increasing use of VL in patients with difficult airways or as a rescue device in failed intubation attempts.[2,3,4,5] Despite a lack of clear evidence suggesting VL improves overall ETI success,[6,7,8,9] VL has quickly become a well-established tool in the armamentarium of the anesthesiologist as well as other healthcare providers (e.g., emergency department, intensive care unit, and prehospital settings) involved in airway management.[10,11]

DIRECT VERSUS INDIRECT LARYNGOSCOPY

Direct laryngoscopy (DL) remains the gold standard technique as an effective means to securing the airway. It is a complicated technical skill with a variable learning curve requiring training, experience, and regular practice to acquire and maintain. DL requires a direct line of sight to align airway axes (oral-pharyngeal-laryngeal) for optimal glottic visualization. Oftentimes, manipulations to align these axes include head extension, neck flexion, laryngeal manipulation, and other stressful movements. Macintosh DL lifting forces can require 35-50 N to expose the glottis. These manipulations of the airway have adverse implications from significant hemodynamic disturbance, cervical instability, injury to oral and pharyngeal tissues, and dental damage.[10]

In contrast to DL, VL utilizes indirect laryngoscopy via its camera; thereby eliminating the need for a direct line of sight to visualize airway structures. In fact, this helps improve glottic visualization.[3,6,12] VL requires the application of less force (5-14 N) to the base of the tongue, therefore is less likely to stimulate stress response and induce local tissue injury.[2,13] Certain videolaryngoscopes (Airtraq^®, Pentax^® AWS [Figures 1 and 2]) have been shown to produce less cervical movement when compared to DL.[14] Furthermore, there is a faster learning curve relative to DL independent of status as a novice or experienced laryngoscopist.[3,6,15] Some data suggests prolonged intubation times with VL as compared to Macintosh DL,[7,9] but there is also evidence on the contrary demonstrating equal and possibly faster ETI times.[2,6]

Figure 1.

The Airtraq SP

Figure 2.

The Pentax AWS

CLASSIFICATION

A variety of device classifications exist, each with their own specifications and interfaces, giving each device its own unique advantages and disadvantages. Evidence remains insufficient to determine which videolaryngoscope performs best: It is highly unlikely that all offer equal benefit, while none are able to achieve 100% success with intubation. A number of review articles have used different designations for classification of videolaryngoscopes.[1,2,3,10,16] The most commonly used classification is: Macintosh-modification, angulated blade, and tube/guide channel.

Macintosh-modification integrates video capability to the traditional Macintosh laryngoscope. For those familiar and experienced with the Macintosh blade, the added advantage is the ability to perform both indirect; and in the case of video failure or secretions on the lens, direct laryngoscopy.[15,17] This may also prove useful to educators in teaching novices of airway anatomy and ETI. These devices do not always require a stylet. Some examples of Macintosh-modification videolaryngoscopes are McGrath^® Mac, Storz^® V-Mac, and Storz^® C-Mac [Figure 3].

Figure 3.

The Storz C-Mac

Devices with an angulated blade incorporate a more angled curvature into the blade which markedly improves glottic visualization with minimal patient head flexion and neck extension.[2,17] The endotracheal tube (ETT), which requires a matching precurved stylet, is carefully introduced and advanced “around the corner” until in monitor view, then maneuvered past the vocal cords at which time the stylet is removed and the ETT juts forth and downward.[11] GlideScope^® GVL [Figure 4], Cobalt, and Ranger, McGrath^® Series 5 [Figure 5], and Storz^® C-Mac D-Blade are examples of angulated blade videolaryngoscopes.

Figure 4.

The GlideScope GVL

Figure 5.

The McGrath Series 5

Tube/guide channel videolaryngoscopes use a guide channel to direct the preloaded ETT towards the glottis. Given the guide channel, a stylet is not necessary. All are designed for oral ETI using a standard ETT. They are highly portable given their small, directly attached video screens on the laryngoscope handle. Examples of tube/guide channel scopes are Pentax^® AWS and Airtraq^®. The Airtraq^® uses an optical lens and if desired allows attachment of the video camera to permit viewing via monitor.

ADVANTAGES VERSUS DISADVANTAGES OF VL

As mentioned, each VL device has its own unique advantages and disadvantages. However, there are generalized advantages and disadvantages to VL.[1,3,10]

Advantages

In general, most VL devices offer the following advantages: Unnecessary to align airway axes (oral-pharyngeal-laryngeal) to achieve line of sight; improved glottic visualization, especially in scenarios with limited mouth opening or neck mobility; higher ETI success rate with non-expert, and possibly expert, laryngoscopists; allows others to view the screen and/or help facilitate ETI (e.g., redirect cricoid pressure, acquire other airway devices); an effective tool for those who infrequently intubate as well as students learning to intubate; less cervical manipulation; possible awake assessment/intubation; and can provide an official record.

Disadvantages

Some disadvantages of using VL devices: Difficulty in passing ETT despite improved glottic visualization (especially with angulated blade); possible increased intubation time; variable learning curve; potential weakening in development/maintenance of DL skill set, especially in nonexperts of airway management; potential for false sense of security and lack of preparation for difficult airway;[3] two–dimensional view with loss of depth perception; obscured view by fogging and secretions on camera lens; more complicated; and expensive.

CURRENT EVIDENCE ON THE USE OF VL

Clinical performance in normal and difficult intubation

It is well established that VL devices improve laryngeal view as compared to DL in patients with suspected difficult intubation (DI) and simulated difficult airway scenarios.[3,6,9] But it is uncertain, whether this translates to increases in overall ETI success rates, especially when DL is difficult or fails.[7,8,9,18]

For instance, two different observational studies of emergent airway management in the Emergency Department (ED) found DL (86-93% success rate) superior to VL with 71.4[9] and 81%[8] success rates using GlideScope^®. Interestingly, in Platts-Mills’ study of 280 ED patients, nine VL failures were rescued by DL, and 17 DL failures were rescued by means other than VL (reason not given).[8] A recent retrospective study of 822 emergent intubations by Sakles et al., found ETI success rate with VL versus DL to be almost equivalent (84 vs 86%, respectively).[19] A similar result was found in the intensive care unit (ICU) setting by Ural et al., when comparing ETI success rates before and after implementation of VL for intubation.[20]

In contrast, some recent publications showed favorable results for VL with high rates of success after difficult or failed direct laryngoscopy using different videolaryngoscopes such as GlideScope^®,[21,22] C-Mac,[22] McGrath^® Series 5,[23] Airtraq^®,[24] and Pentax^® AWS.[5] In their robust study involving 2,004 intubations; Aziz et al., demonstrated a high ETI success rate using GlideScope^® in primary airway management (98%; 1,712 of 1,755), in predicted DI (96%; 1,377 of 1,428), and rescue following failed DL (94%; 224 of 239).[21] Using the Pentax^® AWS, Asai et al., had a 99.3% (268 of 270) ETI success rate, and 95.7% (22 of 23) in predicted DI.[5] Noppens et al., used the McGrath^® Series 5 on 61 patients following Macintosh DL with Cormack/Lehane (C/L) III or IV grades and resulted in 95% ETI success rate in these confirmed difficult airways.[23]

Niforopoulou et al., concluded in their 2010 topical literature review that VL did not offer anything more than Macintosh in easy DL with C/L grades I or II and increases intubation time. However, in difficult airways with C/L grade III or IV it was proven to convert “blind” views into one under visual control and achieved the same or higher ETI success rate with equal or faster intubation time.[2]

Despite the lack of uniformity and need for further investigation, VL continues to gain popularity both inside and outside the operating room (OR). It has quickly become a first line strategy for potential and/or encountered difficult intubation (DI).[2,3,4,5] In some institutions and settings, it has even replaced DL as a substitute for routine cases requiring ETI.[3]

Short learning curve

For novices and experienced anesthesiologists alike, VL is easy to use, and the skills involved are easy to master.[3] It has been determined a 90% ETI success rate with DL requires intubation of 47-56 patients.[25] VL has a much shorter learning curve. Novices trained with Macintosh DL achieved 69 vs 55% ETI success rate with VL (Storz^® V-Mac) versus DL, respectively; while anesthesiologists achieved 99.6% ETI success on first use of the videolaryngoscope.[15] With GlideScope^®, inexperienced operators needed only a few (less than ten) intubations to achieve proficiency with ETI.[6] Anesthesiologists using the GlideScope for the first time had 100% ETI success rate, and 97% of patients were intubated on the first attempt.[26] Similar outcomes were found with Pentax^® AWS where both experienced anesthesiologists and inexperienced operators found ETI to be much simpler when compared to Macintosh DL in manikin trials.[27] Also; a prospective, randomized, cohort study showed less user skill was required with Pentax^® AWS compared to Macintosh, with inexperienced users yielding lower ETI failure rates and faster intubation times.[28]

Cervical spine concerns

A number of studies have been aimed at different videolaryngoscopes to determine their utility in unstable or limited mobility cervical spines. The results have been variable but promising. Two separate studies found less cervical spine motion using the Airtraq^® when compared to Macintosh DL and suggested its use in patients with unstable or limited mobility cervical spines.[29,30] When comparing GlideScope^® to Macintosh DL using fluoroscopy, GlideScope^® did not decrease cervical spine movement, but did reduce the need for optimization maneuvers in patients with manual in-line stabilization.[31,32] GlideScope^® has also been found to facilitate nasotracheal intubation in patients with ankylosing spondylitis.[33] The Pentax^® AWS has also demonstrated less upper cervical spine movement, and even less when aided by gum bougie, as compared to DL.[34,35]

Nonoperating room/off-site use

Patients requiring ETI in nonoperating room or off-site settings (ED, ICU, prehospital) are typically emergency situations associated with hemodynamic compromise. These patients often meet ASA III or IV classification,[36] and have a much higher risk of difficult laryngoscopy and intubation even when operators have adequate airway skills.[37] Furthermore, the risk of complications associated with poor glottic visualization (C/L grades III or IV) is twice as high outside versus inside the OR.[38]

These risks compound further when inexperienced or nonexpert providers are responsible for securing the airway under such challenging conditions. Studies with nonexperts have shown increased first-attempt success and decreased time to intubation with GlideScope^® compared to DL.[6,39,40] Paramedics described easier ETI when using VL rather than Macintosh DL in two manikin studies.[41,42] In the field, paramedics using the GlideScope^® Ranger performed successful ETI in less time and with less attempts as compared to DL, though the overall success rate was equivalent.[43] Therefore, VL technologies that improve visualization and ETI success rates, especially in nonexpert operators, could help minimize sequelae and maximize patient safety during laryngoscopy for ETI.

Obesity

Patients with morbid obesity (body mass index ≥ 40 kg/m²) are more commonly associated with DI than normal-weight patients.[44] Maassen et al., randomized obese patients with three different videolaryngoscopes (GlideScope^® Ranger, Storz^® V-Mac, McGrath^® Series 5) to compare to Macintosh DL. All VL devices offered equivalent or improved glottic views, with Storz^® V-Mac yielding better overall satisfaction score, intubation time, number of intubation attempts, and necessity of extra adjuncts (e.g., stylet).[45] In a randomized trial of 106 morbidly obese patients, Airtraq^® shortened the duration of tracheal intubation and prevented reductions in arterial oxygen saturation when compared to Macintosh DL.[46] Also, as a substitute to fiberoptic bronchoscopy in anticipated DI with morbidly obese patients, the GlideScope^®,[47] Airtraq^®,[48] and Pentax^® AWS[49] have been successfully used in topicalized patients undergoing awake intubation.

Teaching

VL can serve as a teaching and supervising tool for tracheal intubation with its real-time displays during laryngoscopy. It allows for viewing and magnification of the airway anatomy and any associated anomalies. Instructors can provide feedback for novice laryngoscopists to overcome difficulties related to DL and tube insertion, and also help with airway manipulations if necessary. Macintosh-modified videolaryngoscopes allow novices to perform both direct and indirect laryngoscopy, while the instructor can take advantage of the monitor's view to provide guidance and feedback.[50]

Other VL applications

Awake intubation using VL not only has application in obese patients, but can be used in difficult airway situations warranting an awake inspection or intubation. Due to the decreased amount of pressure applied to the base of the tongue, topicalized awake patients can tolerate VL. However, further studies are needed to compare outcomes of VL to the gold standard fiberoptic bronchoscopy.[51]

Using VL to visualize and facilitate, a more confident ETT exchange has been described. Using the Airtraq^®, exchange of ETT over a gum elastic bougie or Cook catheter was performed in critically ill, difficult intubation patients.[52] GlideScope^® GVL has successfully been used in ETT exchange from nasotracheal to orotracheal in a patient with airway mass.[53]

Other reported applications of VL include foreign body removal from the hypopharynx,[54] intubating in the setting of epiglottitis,[55] placement of a double-lumen tube,[56] and facilitating percutaneous tracheostomy.[57]

Limitations and complications

Difficulty may be encountered with inserting certain VL devices into the oral cavity. The angulated blade of GlideScope^® GVL requires a greater tilt of the handle to enter the oropharynx. Various patient factors (e.g., obesity, large chests/breasts, short neck, etc.) can make achieving this tilt a challenge. A similar problem can be seen with Storz^® V-Mac due to its large handle with emerging cables. Certain techniques can be employed for these VL devices to overcome such shortcomings. For example, blade insertion of the GlideScope^® GVL can be improved by further extending the atlantooccipital joint and rotating the handle 90° to the right.[26]

Despite an improved glottic view, ETT insertion may be problematic especially with angulated blade video laryngoscopes.[11,26] This difficulty is because indirect laryngoscopy does not require alignment of the airway axes, thus the need for the ETT to be inserted ‘around the corner’. Use of a stylet and proper contouring of ETT is needed to facilitate passage through the vocal cords,[11] though this is not needed in tube/guide channel videolaryngoscopes. Upon passing the vocal cords, the ETT may abut against the anterior aspect of the subglottic trachea. Further, maneuvers and adjuncts may be required to advance the ETT such as cricoid pressure, slight withdrawal of stylet, rotating the ETT, and use of gum elastic bougie.[2,11]

Instrument insertion into the oropharynx and ETT insertion passed the vocal folds into the trachea can be rendered more difficult by certain physical factors. Using GlideScope^® GVL, Aziz et al., found the strongest predictor for ETI failure was altered neck anatomy with presence of surgical scar, radiation changes, or a mass.[21]

A number of complications have been reported using videolaryngoscopes. Damage to the soft palate,[58] palatopharyngeal arch,[59] and palatoglossal arch[60,61] has been associated with GlideScope^® use. Some explanations for these injuries are using greater force than necessary, a rigid stylet, and blades that are too large. Also, injuries can occur by blind advancement of the styletted ETT before being in the video camera's field of view.[60] Another possibility is the operator placing all their attention on the monitor and blindly attempting instrument insertion into the oropharynx.

THE FUTURE OF VL

Despite the need for further studies regarding the optimal applications and overall outcomes, the future of VL is promising. Whether VL will replace traditional laryngoscopy is controversial. However, the American Society of Anesthesiologists (ASA) has already incorporated VL as an adjunct to ‘Alternative Difficult Intubation Approaches’ in their practice guidelines for management of the difficult airway.[62] It has further been suggested that VL may improve safety by avoiding many unnecessary attempts and facilitate learning of both DL and VL.[3] Thus, its role is still evolving. Though it is clear that VL expands the armamentarium not only for anesthesiologists but also for healthcare providers who are potentially involved in airway management.

CONCLUSION

The approach to airway management has undergone a dramatic transformation since the advent of VL. Videolaryngoscopes have quickly gained popularity as an intubation device in a variety of clinical scenarios and settings, as well as in the hands of airway experts and nonexperts. Their indirect view of the upper airway improves glottic visualization, including in suspected or encountered difficult intubation. Yet, more studies are needed to determine whether VL actually improves ETI success rates, intubation times, and first-attempt success rates; and thereby a potential replacement to traditional direct laryngoscopy. Furthermore, advances in technology have heralded a wide array of models each with their own strengths, weaknesses, and optimal applications. Such limitations need to be better understood and alternative strategies should be available. Thus, the role of VL continues to evolve. Though it is clear VL expands the armamentarium not only for anesthesiologists but also for all healthcare providers potentially involved in airway management.