**4.2 Morbid obesity**

Obesity and morbid obesity can complicate airway management. Impaired glottis visualization [97–102] leads to greater lifting force and external laryngeal pressure. Several prediction algorithms have been proposed for the morbidly obese patient [103–105], including anthropometric parameters [106–109]. Body mass index and neck circumference are commonly used to predict difficult airways [110–113], although some studies showed no association with difficult intubation [114]. Still, it is a general consensus that morbid obesity makes tracheal intubation difficult [109]. There are various intubating modalities for obese patients [115–120] and VL is superior to conventional DL [121–130]. VS is useful in morbid patients due to its improved visualization of the larynx and the ease with tube advancement [131, 132].

Our clinical experiences support the role of VS in morbidly obese patients. **Figure 19** shows tracheal intubation with VS in a patient whose oropharynx was too narrow for laryngoscopy (**Figure 19F**). In the last six years, we have performed hundreds of intubations on morbidly obese patients (including more than 100 patients undergoing bariatric surgery), and there were only two cases that we were not able to intubate with VS. **Figure 20** shows three examples of the application of VS in morbidly obese patients (BMI 36.6, 49.9, and 58.4 kg/m<sup>2</sup> , respectively). The

#### **Figure 18.**

*Close-up views from VS in the same patient from Figure 17. Due to limited effects of jaw-thrust maneuver in the presence of radiation fibrosis of the neck, the oro-pharynx (A and B), larynx (C and D) are crowded. The epiglottis curls inward and manifests omega-shaped folding (C). (E) The glottis opening is narrow. (F) ET tube is secured into trachea. The intubation time is 24 s. (Also see the Supplementary Materials Video S15).*

#### **Figure 19.**

*A 65-year-old morbidly obese man with BMI 40.5 kg/m2 (167 cm, 113 kg). (A) Modified Mallampati test: Class 3. Mouth opening 5.5 cm. (B) Thyromental distance: 6.5 cm. Sternomental distance: 11.5 cm. Neck circumference: 47 cm. Upper lip bite test: Class 1. (C–H) Serial views from VS camera. (C) View of oropharynx. (D, E) laryngeal inlet is crowded with LQS score grade 1. (F) Without jaw-thrust maneuver, the LQS class is grade 2. (G, H) Clear visualization of glottis and tracheal rings. The intubation time (for demonstration) is 30 s. (Also see the Supplementary Materials Video S16).*

#### **Figure 20.**

*Serial close-up views from VS in three typical morbidly obese patients. (A) BMI 36.6 kg/m<sup>2</sup> (170 cm, 106 kg). A 37-year-old man underwent laparoscopic hernioplasty. The intubation time is 20 s. (B) BMI 49.9 kg/m2 (165 cm, 136 kg). A 37-year-old woman underwent laparoscopic sleeve gastrectomy. The intubation time is 20 s. (C) BMI 58.4 kg/m2 (167 cm, 163 kg). The intubation time is 22 s. It is interesting to note that the LQS grading scores in all these three morbid obesity cases are grade 1. It is noted that laryngeal tissues are crowded. (Also see the Supplementary Materials Video S17–S19).*

intubation with VS technique was smooth and fast. The "video-video paired technique" will be presented in the latter part of this article.

### **4.3 Restricted cervical spine mobility**

Restricted cervical spine (C-spine) mobility is a major risk factor for difficult airway in various prediction algorithms. Although awake/asleep/anesthetized flexible fiberoptic bronchoscopy is the gold standard for airway management, other airway modalities and tools have been proposed in the literature [133]. Among all the airway tools, VL has drawn the most attention as a useful tool for restricted C-spine motion. This technique has been tested in patients with a simulated restricted C-spine condition (with manual in-line stabilization or rigid cervical collar) [44, 134–145], in real patients undergoing C-spine surgeries [146, 147], and in mannequin simulation model [148, 149]. Recently, VS has also been tested in patients with simulated restricted Cspine motion [31, 78, 80, 81, 84, 150, 151].

Our single-institute clinical experience (more than 600 C-spine surgeries a year) indicates that the VS technique is a very useful technique in this patient population. **Figure 21** shows a case when cervical spine mobility was restricted by the neck collar. Another example of limited C-spine mobility is in patients receiving stereotactic neurosurgeries with a head frame mounted before tracheal intubation can occur. **Figure 22** shows such a scenario.
