**2. Clinical experiences of optical intubating stylet**

#### **2.1 Airway grading**

It is sometimes challenging to get a proper view of the glottis during routine tracheal intubation using DL. A simple prediction scale is therefore necessary and quite helpful in assessing and predicting risk during tracheal intubation [16–18]. We use the modified Cormack–Lehane (C–L) grading system of glottis view [19] to predict difficulty of tracheal intubation [20]. Modified scoring methods have also been used in our practice (e.g., percentage of glottis opening scale) [21, 22]. In addition to the competency in intubation technique, the quality of the airway assessment (e.g., difficult airway predictability) made by airway operators is also crucial for a successful intubation.

#### **2.2 Preparation for placement of endotracheal tube**

VS technique provides a superior view of the vocal cords and continuous visualization of the glottis for an easy and precise placement of the ET tube, as compared to DL and VL (**Figure 3B**). There are, however, some potential issues to be aware of when using VS: (1) Possible fogging of the lens (**Figure 5A**), which by the way can also happen with VL [23–26]. This is easy to prevent by careful wiping out the tip-lens with an anti-fog before use (**Figure 5B** and **C**). (2) Mucus or saliva covering the lens, and a good preventive maneuver is to keep the stylet a few millimeters proximal from the tip of ET tube, hence protecting the lens of the stylet. **Figure 5C** shows the appearance of the Murphy eye of an ET tube (side vent near the distal end of an ET tube) on a LCD screen. It should be emphasized that good video screen visualization is important for successful tracheal intubation when an optical stylet is used [27].

**Figure 5.**

*The tip of VS should be kept clean and clear before use. (A) The optical lens was obscured and caused blurred vision. (B) Clear view after cleaning. (C) The relative position of the tips of the video stylet and endotracheal tube. The stylet tip was a little more backward than its position in (B).*

### **2.3 Entrance to oral cavity**

Since its original introduction in 1996 [6], numerous papers have been published on the application of the VS along with its advantages and benefits [13, 28–31]. An actual operating scenario for the Shikani technique of intubation is briefly described below. The operator first lifts up patient's mandible with the left hand and displaces it anteriorly until the lower teeth are anterior to the upper teeth (**Figure 6A**). The stylet-loaded ET tube set is then advanced forward by the right hand until the epiglottis is seen on the monitor. The operator can then maneuver the stylet beneath and pass around the epiglottis while continuously visualizing the airway. This allows a smooth and atraumatic railroading of the ET tube through the glottis and into the trachea. Occasionally, the tongue is large and in the way and the glottis cannot be seen clearly. In these situations, combining a Macintosh blade would further open the upper airway and bring the glottis into view. Alternatively, in contrast to the single-handed chin lift maneuver, a twohanded jaw thrust aided by an assistant can be used to facilitate the VS intubation (**Figure 6B**). With this strategy, the assistant stands either side by side or opposite the operator [32, 33]. It should be cautioned that the BURP (backward, upward, rightward external laryngeal pressure) is not helpful or recommended for VS technique. The combined use of VL or DL was also reported using the Bonfils rigid endoscope [34] or a lighted stylet [35]. **Figure 6C** shows the combination of DL and VS. Detailed description of such combination method will be presented in the latter part of this article.

#### **Figure 6.**

*Three methods to perform the VS technique. (A) Classical Shikani method. (B) Two-person performance. An assistant stood side by side with the operator (or opposite the operator) to provide jaw-thrust maneuver. (C) Combined use of laryngoscopy and VS technique. All three maneuvers can open patient's airway and enlarge retropharyngeal space for further advancement of the video stylet.*

#### **2.4 Glottic view**

While the original and modified Cormack-Lehane grading system are useful [36], they are clinically meaningful and transferrable only if optimal intubating technique (e.g., optimal blade and its position, lifting force, head/neck position, external laryngeal manipulation, awake or anesthetized) is employed [37]. The main purpose of the C-L grading system is to describe the glottic view during direct laryngoscopy and might not necessarily translate to ease and speed of tracheal intubation. When VL was introduced [38], some reported that it had higher rates of successful intubation on the first attempt with improved glottic views, as compared to DL [7]. However, in different clinical settings (e.g., in emergency room or intensive care unit) and different patient populations (e.g., pediatric patients), VL did not show its superiority in firstpass success rate and time to intubation, as compared to DL [39].

In contrast to DL and VL, VS seems to provide the best glottic view as the tip of the stylet can access the laryngeal inlet and be positioned beneath the epiglottis. Because the vocal cords are directly visualized, the passage of the stylet-ET tube into trachea is almost assured. This allows minimal (if any) trauma while circumventing any laryngeal pathology such as cysts, tumors, etc.

We believe the glottis visualization grading systems for VS technique should be simply graded as "easy, restricted, and difficult". The crux of the matter in airway intubation is "to see is to accomplish". If the vocal cords can be seen, the placement of ET tube is then easy. We propose such a grading system (LQS system) specific for VS technique shown in **Figure 7**.

#### **Figure 7.**

*LQS grading score on glottis visualization by VS technique. Grade 1: Able to see any part of the vocal cords and arytenoid cartilages. Grade 2: None of glottis parts can be seen. Only epiglottis can be seen and there is enough space left between the epiglottis and posterior pharyngeal wall. Grade 3: The space under the epiglottis is very narrow and probably will create difficulty passing the stylet. It should be emphasized that once the stylet can be introduced beneath the epiglottis, full glottis view can be obtained (images shown in the lower row). This is a case for doublelumen endobronchial tube placement. Intubation time (for demonstration purposes): 28, 26, and 30 s, respectively. Please also compare with Figure 8. (Also see the Supplementary Materials Videos S1–S3. To watch the supplementary videos contact the email address: lukairforce@gmail.com).*


The majority of the cases (74%) fell into grade 1 (**Figure 7**, left panel), 25% into grade 2 (**Figure 7**, middle panel), and very few (1%) classified into grade 3 (**Figure 7**, right panel) that required more laborious maneuverability to pass the stylet-ET tube set through the glottis. Our proposed grading method (LQS grading score), similar to other systems (e.g., C–L score, POGO score), does not require exact knowledge of grading minutiae (e.g., subdivided into 2a, 2b, 3a, 3b) [36, 40]. Our clinical experiences of the use of VS for routine and emergency intubation indicated that the LQS grading system was correlated with various intubating outcomes, such as intubating time, first-attempt success rate, easiness, complication rates, etc.

In our experience using the VS technique, we encountered some problems that caused the intubation to be more difficult, including: (1) copious mucus and saliva obscuring the lens and views; (2) stiff neck and restricted cervical mobility limiting the jaw-thrust; and (3) swollen soft tissues and floppy epiglottis hindering the pass of the stylet-ET tube either from midline or from the side of epiglottis (**Figure 8B**, left panel). In those difficult cases, the FOB technique may be helpful (**Figure 8B**, middle and right panels).

It should be emphasized that the LQS grading system is for VS technique combined with the simple jaw-thrust maneuver and may be affected by various patient conditions (e.g., restricted head/neck motility, pathological obstruction of airway, efficiency of jaw-thrust maneuver). Therefore, in patients with simulated difficult airway (e.g., using cervical collar or manual in-line stabilization) and a confirmed a high C–L grade by DL, the subsequent use of VS may take a longer time [41]. However, similar high intubation success rates with VS technique were obtained in both low C–L grade and high C–L grade patients in the simulated difficult airway scenario. During such intubation with VS, visualization of vocal cords and advancement into the glottis for the high-grade group was significantly more difficult than in the low-grade group [41].

In patients with a large and floppy epiglottis (i.e., LQS grade 3), the view can be improved by simply applying a jaw-thrust maneuver or by combining with a Macintosh blade [42, 43]. **Figure 9** shows such an example using a jaw-thrust maneuver to lift up the epiglottis for passage of the stylet-ET tube set. In this case, the

#### **Figure 8.**

*Two uncommon cases seen from VS camera. (A) Case 1: An 89-year-old woman. The glottis is perfectly visualized simply by jaw-thrust maneuver and the vocal cords fully open and visible (i.e., Cormack-Lehane class 1, POGO 100%). (B) Case 2: A 75-year-old man. The epiglottis could not be lifted up at all by jaw-thrust maneuver due to severe radiation fibrosis of the neck. The epiglottis is labeled by the yellow star. Left panel: The epiglottis was completely attached to the posterior pharyngeal wall when the patient was anesthetized and paralyzed. Intubation with VS technique failed after several attempts. Middle panel: The patient was quickly reversed from anesthetized status to asleep status with spontaneous respiration. Rescue intubation was eventually achieved by FOB. The epiglottis still remained drooped. Right panel: Three weeks later, the same patient received elective tracheostomy due to difficulty breathing. Awake nasal intubation was done with FOB. The patient in Figure 8B is the same as in Figures 36–40.*

#### **Figure 9.**

*Effect of jaw-thrust maneuver on improving glottis view seem from VS. this is a 66-year-old man with a BMI 25.0 kg/m2 (167 cm, 70 kg). Mallampati score: Class 2. Neck circumference 44 cm. (A) View of oral cavity by opening mouth. (B) View of pharynx entry and uvula. (C) Laryngeal inlet. (D) Jaw-thrust created a LQS score grade 1 with partial view of glottic region. (E) Without jaw-thrust maneuver, epiglottis stayed back and attached to posterior pharyngeal wall. (F) Close-up panorama view of glottis. Intubation time (from lip to trachea, for demonstration): 30 s (Supplementary Materials Video S4).*

oro-pharyngeal-laryngeal space/inlet was open and accessible (**Figure 9A**–**C**). However, jaw-thrust could only lift up the epiglottis to expose the vocal cords less than 50% (**Figure 9D** and **E**) in this patient. Once the space underneath the epiglottis was wide enough to allow VS passage, the vocal cords could easily be viewed fully (**Figure 9F**). Further placement of the ET tube was easy by railroading the tube from VS.

#### **2.5 Time to intubation**

A mounting body of evidence indicates that VL reduces the rate of failed intubation and results in higher rates of successful intubation on the first attempt with an improved glottic view [7]. In patients with anticipated difficult airways (e.g., cervical collar limited mouth opening and neck movement), VL was safe and quicker in controlling the airway (time to view the vocal cords: 20–30 s (median); time to advance tube 30–40 s (median); intubation time of successful attempt: 50–60 s) [44]. The reported intubation time for emergency intubation by VL is 60 s 31 s (difficulty score with Visual Analogue Scale 0–100: 39 27) [45]. In adult patients with a normal airway, the time for successful tracheal intubation with VL is short (17–38 s) [46]. Similar time ranges were found for emergency intubation with VL in these patients (12–15 s) [47].

**Figure 10** shows four examples of the use of VS technique in patients with normal airways under routine tracheal intubation for elective surgeries. In two patients who needed rapid sequence intubation, the intubation time (from lip to trachea) using VS was 5–7 s, respectively (**Figure 10**, the left two panels). For teaching purposes or if there is a need to "look around the corner", the intubation time was slowed down to 20–30 s (**Figure 10**, the right two panels). If the intubation takes a longer time

#### **Figure 10.**

*Time to intubation (from lip to trachea) using VS technique in four examples. Upper row: View from epiglottis. Lower row: Close-up view of glottis. Left (5 s): A 36-year-old man with BMI 22.7 kg/m<sup>2</sup> (178 cm, 72 kg). Second from the left (7 s): A 52-year-old woman with BMI 24.0 kg/m<sup>2</sup> (162 cm, 63 kg). Third from the left (20 s): A 42-year-old man with BMI 29.3 kg/m2 (174 cm, 89 kg). Right (30 s): A 55-year-old man with BMI 23.0 kg/m2 (164 cm, 62 kg). It is noted that the speed of intubation was deliberately slowed down (20 and 30 s) for demonstration purpose. (Also see the Supplementary Materials Videos S5–S8).*

(e.g., between 30 and 60 s), the operator should anticipate a potentially difficult intubation (e.g., **Figure 8B**) and a plan B should always be prepared.

During airway management, the airway is not always as clear as seen in **Figure 10**. In the real world, the airway operator using VS technique might encounter copious thick mucus, saliva, or sometimes blood in the airway. Those secretions may obscure the lens of the optical intubating tool and make intubation more difficult. Frank emesis and massive vomitus or blood can occur in certain traumatic emergencies [48, 49]. Quick, effective, and continuous suctioning of pharyngeal secretions or blood is necessary to reduce the risk of losing visualization. A tracheal suction catheter or Yankauer suction tip would help clearing the oropharynx and larynx. **Figure 11** shows the saliva impeding the glottic view when VS technique was applied. Premedication with an anti-sialagogue and proper suctioning are helpful to reduce such problems before inserting the optical stylet into the patient's oropharynx.
