**4. First-line choice of VS in difficult airway**

Over the last decade, the VS technique has been widely used as an alternative to VL in simulated difficult airways (e.g., rigid cervical collars applied) [6, 31, 76–83], cervical spine surgeries [84, 85], upper airway obstruction [86–89], double-lumen endobronchial tube placement [90–92], and emergent awake intubation [93]. In the following sections, we present our clinical experiences of using the VS technique as the first-line intubating modality in several difficult airway scenarios.

#### **4.1 Head neck lesions**

Various video-assisted intubating stylets have been used in potential or anticipated difficult airway as the first-line tool for tracheal intubation. We previously reported use of VS in patients with anticipated difficult airway, such as facial-oral tumors, enlarged tonsils, radiation neck fibrosis, hypopharyngeal cancers, and laryngeal tumors and cysts [94]. Similarly, VS was also reported in patients with an epiglottic cyst [86, 87], retropharyngeal tumor [88], and in awake nasal intubation [89].

Although awake/asleep flexible fiberoptic bronchoscopy and elective/emergency tracheostomy still remain the gold standard of the airway management in extreme difficult airway (e.g., hypopharyngeal cancer, severe radiation-induced fibrosis over neck, giant neck tumors, restricted mouth opening), VS can play a role in anticipated difficult airway, similar to the proposed role of awake FOB and VL [95]. One advantage of the Shikani stylet over the fiberoptic scope is the ability to maneuver it around a floppy epiglottis, especially if the patient is asleep and in the supine position. It should be mentioned that rigid endoscopy is one of the difficult airway rescue modalities [96].

**Figure 15** shows an example of a potential difficult airway in a patient with hypopharyngeal cancer undergoing laryngo-microsurgery (LMS) intubated with VS. The epiglottis was difficult to lift up but the space between the epiglottis and posterior pharyngeal wall was just wide enough to allow the stylet-ET tube set to go through. A good glottis view was obtained, and intubation was completed without delay. When VS is used in patients with head/neck lesions, the operator should expect that mucus and blood can blur the lens of VS and be prepared to handle that (**Figure 16**).

When a patient has been previously treated with radiotherapy or surgery, a stiff neck caused by radiation fibrosis, flap, or scar is expected. In **Figure 17**, the patient's mouth opening was wide enough, but the neck was stiff and the cervical spine

#### **Figure 15.**

*Use of VS technique in a patient with anticipated difficult airway. A 66-year-old man (BMI 22.6 kg/m2 ; 164 cm, 61 kg) with hypopharyngeal cancer underwent LMS surgery. (A) and (B) Pre-operative endoscopic survey images. (C–H): Serial views during tracheal intubation using VS under general anesthesia. The epiglottis could not be fully lifted up by sole jaw-thrust maneuver (D). The intubation time: 20 s. (also see the Supplementary Materials Video S13).*

#### **Figure 16.**

*Use of VS technique complicated by a saliva bubble in a patient with hypopharyngeal cancer. This is a 57-year-old man with BMI 26.0 kg/m2 (172 cm, 77 kg). The intubation time: 20 s. (Also see the Supplementary Materials Video S14).*

#### **Figure 17.**

*Use of VS technique in a patient with stiff neck caused by radiation therapy. This is a 72-year-old man with BMI 20.4 kg/m2 (174 cm, 62 kg). He had squamous cell carcinoma over the neck with metastasis and received definitive concurrent chemoradiotherapy. (A) Mouth opening is wide enough. (B) Stiff neck due to radiation fibrosis with ulceration. (C) Post-intubation. (D) Post-operation after extubation.*

mobility was restricted. His glottic inlet was narrow due to edema of the pharyngeal tissues and epiglottis. The intubation was nevertheless smoothly executed using VS technique (**Figure 18**).
