Tracheal Intubation Using Optical Stylets
Rania B. Fashir
Khader S. Zimmo
Orlando Hung
INTRODUCTION
While tracheal intubation under direct laryngoscopy using a straight blade (Miller laryngoscope), or a curved blade (Macintosh laryngoscope) is very effective, visualization of the glottis still may not be possible in a small number of patients. During the past several decades, many airway devices, techniques, and adjuncts have been developed to address this situation, such as combination techniques (laryngoscope + flexible endoscope, bougies, etc.). The alternative devices, including the optical stylets, have proven to be effective, safe, and have played important roles in managing patients with a difficult or failed airway.
Optical stylets were first described by G. Katz and R. Berci in 1979.1 They claimed that during direct laryngoscopy, the endotracheal tube (ETT) could partially block the view of the larynx and the procedure was performed semiblindly. They also claimed that a design with a rigid, straight optical instrument that allowed the airway practitioner “to see through” the ETT could improve the intubation success rate. They referred to this instrument as the “optical stylet” which combines features of rigid bronchoscopes and intubating stylets. At the time of its introduction, it was extensively used for teaching purposes; however, its rigid straight design limited its use in managing difficult airways. There have been several modifications introduced to the original design which increased its utility in the clinical realm.
These optical stylets can facilitate tracheal intubation with or without the use of laryngoscopes or extraglottic devices (EGD). Since their introductions, many types of optical stylets have been designed. They vary in light source, length, shape, external diameter, and malleability. Newer optical stylets do not use optical fibers. Instead, they use the CMOS video-chip technology. They are malleable and they usually have a small monitor attached to the handle or allow an attachment to a smartphone, thus improving their portability.2 This chapter is not an exhaustive review of all available optical stylets and we will only discuss the different types of optical stylets with clinical evidence.
DESIGN CHARACTERISTICS OF OPTICAL STYLETS
The optical stylet is composed of a thin rigid or semirigid (malleable) shaft that transmits light distally and the image proximally to an eyepiece or a display. Light is generally powered from a battery source to enhance portability, although some devices can be attached via a cable to a remote light source.
On most devices, an ETT holder is located on the proximal end which is compatible with a standard 15-mm ETT connector. The tube holder can be adjusted on the stylet shaft to accommodate different ETT lengths, enabling appropriate positioning of the tip of the endoscope just within the distal end of the ETT (Fig. 26.1).
 Figure 26.1: The Shikani Optical Stylet. |
The distal objective lens located at the tip of the optical stylet is responsible for focusing objects. This lens possesses an angle of view, representing the cone-shaped visual field. A larger angle provides a more extensive panoramic view. Optical stylets typically offer angle views ranging from 50 degrees to 100 degrees. The wider angles are beneficial for identifying the glottic opening when the stylet tip is off-center or encounters an anterior or deviated glottis. All optical stylets have distal lenses with a focal length of 5 to 50 mm, which is suitable for intubation purposes. None of the optical stylets have a hollow working channel for suction.
All optical stylets are susceptible to fogging and should be prepared with an antifogging solution or warmed prior to use.
TYPES OF OPTICAL STYLETS
The Levitan FPS optical stylet (Clarus Medical LLC, Minneapolis, MN) was designed to be used in conjunction with laryngoscopes in routine or difficult intubations (Fig. 26.2). It can accommodate an ETT with internal diameter (ID) of 5.5 mm or greater.3 There is an available oxygen insufflation port, and the light source can be provided by an LED light or a GreenLine laryngoscope handle. Its main feature is its short malleable stylet which requires cutting of the ETT to 27.5 cm.4 This short length facilitates ready positioning of the device in front of the operator’s eye during the process of direct laryngoscopy when facing a challenging view (Cormack-Lehane grade 3 view).5
Figure 26.2: The Levitan Optical Stylet can be shaped to 90 degrees.
Aziz et al.,6 conducted 315 consecutive intubations using the Levitan FPS as a solo device, in the operating room. Successful intubation rate was 99.7% with a mean intubation time of 23 seconds. Rate of complications which were described as minor airway trauma was 1%.
The Levitan FPS and Bonfils were compared in a study by Webb et al.7 The study compared effectiveness of each stylet in cases of predicted routine airways, in the hands of anesthesiologists with no prior experience using optical stylets. There was no significant difference in their effectiveness; however, there was a high failure rate (5.6%). The challenges encountered by the operators include secretions, fogging, and resistance when passing through tissues.7 This study emphasizes the importance of skill acquisition prior to the introduction of the Levitan FPS optical stylet for routine clinical use.
Shikani Optical Stylet (Clarus Medical LLC, Minneapolis, MN) is a semimalleable stylet for routine and difficult airway management (Fig. 26.2). It can be used with or without a
laryngoscope or insertion through an EGD device. The stylet shaft is 27 cm long with an external diameter of 5.0 mm. It can accommodate an ETT of 5.5 mm or greater.3 The pediatric version is compatible with ETTs in the 2.5 mm to 5.5 mm ID range. The eyepiece can be attached to a camera system for display on a larger screen.
In a randomized controlled trial8 involving 60 patients undergoing anesthesia with a simulated difficult airway, the Shikani optical stylet was investigated as an alternative to the Glidescope video laryngoscope (GVL). All patients had rigid cervical collars applied to mimic a challenging airway. The study demonstrated that intubation was successful in all patients, with a first-attempt success rate of 97% in the GVL group and 93% in the Shikani group. The average duration for successful intubation time to intubation (TTI) was 64 seconds when using the GVL, and 58 seconds in the Shikani group. These findings indicate that the Shikani optical stylet offers a comparable TTI with a high success rate and potentially lower risks of oral mucosal injury, compared to the GVL, in patients with a simulated difficult airway.
The Bonfils Intubation Endoscope (Bonfils, Karl Storz Endoscopy Canada Ltd., Mississauga, Canada) has a straight, nonmalleable shaft with a fixed 40 curve at the tip,3 and a movable tube holder, intended for use via retromolar approach (Fig. 26.3). The adult version accommodates an ETT of 5.5 mm or greater ID. Smaller pediatric versions are available.
Figure 26.3: The Bonfils Retromolar Intubation Fiberscope loaded with an ETT.
One of its first clinical utilities was tracheal intubation in children with Pierre Robin syndrome.9 The pediatric version comes in two sizes: an external diameter of 2 mm which can accommodate ETT size up to 3.5 mm ID, and the other with an external diameter of 3.5 mm which can accommodate an ETT size of >3.5 mm ID.
Byhahn et al.10 conducted a study comparing the Bonfils scope with the Macintosh blade for tracheal intubation in elective gynecologic patients with simulated difficult airways. The patients’ mouth opening and neck movement were restricted using rigid cervical collars. Out of the 76 patients included in the study, the authors found that successful intubation was achieved in only 39.5% of cases using the Macintosh blade, while the Bonfils scope had a success rate of 81.6% within two attempts.10
Wahlen and Gercek11 conducted a study comparing the time to intubation using the Bonfils scope and the Macintosh blade in patients with normal cervical spines. The results showed that intubation was faster with the Macintosh blade (18.9 ± 7.1 seconds) compared to the Bonfils scope (52.1 ± 22.0 seconds). All patients had successful tracheal intubation on the first attempt with the Macintosh blade, while the success rate of the Bonfils scope was 91.7%. The advantages of using the Bonfils scope may be more evident in patients with limited neck movements and mouth openings. Wahlen and Gercek demonstrated that the faster intubation achieved with the Macintosh blade was associated with greater movement of the cervical spine (22.5 ± 9.9 degrees) compared to the Bonfils scope (5.5 ± 5.0 degrees), which may not be desirable in certain patient groups.11
Clarus Video System (CVS) (Clarus Medical LLC, Minneapolis, MN) is a video-based optical malleable stylet with an attached 4-inch LCD screen mounted at the proximal end (Fig. 26.4). It can be used as a solo device, to assist with DL/VL intubations or via an extraglottic airway device (EGD). The scope has two light sources: two white LEDS and one red LED for transillumination through the patient’s skin.
Figure 26.4: Optical malleable stylet.
Kim et al.12 demonstrated use of the CVS in patients whose necks were immobilized by cervical collars resulted in shorter time to intubation when compared to the Airway scope (18.9 vs. 30.4 seconds). It provided faster and easier intubation and had comparable success rates with no difference in number of attempts, complications, or hemodynamics.
It has been evaluated for use in awake intubation of difficult airways,13 in rapid sequence intubation (RSI),14 and placement of double-lumen tubes with success.15 In addition, it has the advantage of being an easy airway tool to learn to use as demonstrated by Moon et al.16 It was found that 10 intubations were sufficient to properly learn the use of the CVS without causing trauma and ensuring first-pass success.
The C-MAC Video Stylet (VS) (KARL STORZ Endoscopy Canada Ltd., Mississauga, Canada) is a newly developed video endoscope that features a semiflexible sheath and deflectable tip that can angle up to 60 degrees via a lever on the handle, with passive return (Fig. 26.5). The stylet can accommodate ETT >6 mm. In addition, it includes an adjustable adapter for ETT fixation and oxygen insufflation. The device is designed to connect to a C-MAC monitor to display the captured images. The C-MAC Video Stylet is primarily used for difficult airway management.
Figure 26.5: The C-MAC® video stylet connecting to a C-MAC® monitor for image display.
(Courtesy KARL STORZ.)
Given the novelty of the device, limited studies have reported on its use. Nabecker et al.17 aimed to determine the feasibility of successful awake orotracheal intubation in adult surgical patients with known or predicted difficult airway. The investigators demonstrated an overall success rate of 97% and a first-attempt success rate of 80% (29/36) when used for orotracheal awake intubation in anticipated difficult airways. Case reports have also demonstrated its optimal use, given its thin profile, in patients where there is limited mouth opening precluding the use of DL or VL.18
In a manikin trial with a simulated difficult airway conducted by Pius et al.,19 the investigators found that the learning curve was comparable between VL (with a Macintosh blade) and VS. In addition, the median total time to intubation was faster with the VS compared to VL (17 [13.5-25] sec vs. 23 [18.5-26.5] sec, respectively; 95% CI; P = .031).
Its design was created for intuitive handling. While preliminary studies show promise with the device, further studies are necessary to confirm its clinical utility in airway management.Related posts:
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