**6.8 Ultrasound-guided prediction of left-sided DLT size**

Outer tracheal ring diameter is a useful predictor of left main bronchus diameter on ultrasonography and hence helps in selecting left-sided DLT.

*Ultrasound (US) Imaging Use in the Management of the Difficult Tracheal Intubation DOI: http://dx.doi.org/10.5772/intechopen.108465*

#### **Figure 5.**

*US image showing trachea (yellow), esophagus to its right (green) and the carotid (red). (image credits: Author Dr Venkata Ganesh).*

### **6.9 Ultrasound-guided detection of laryngeal mask airway position**

With the help of US, position of the LMA cuff can be confirmed. For adequate ventilation, the LMA cuff should be placed at the proper position to seal the larynx. LMA should be repositioned if it is not visualized equally on both sides of the larynx on ultrasound [18].

## **6.10 Ultrasound-guided diagnosis of upper airway pathologies**

The US can be used to assess and diagnose upper airway inflammatory diseases such as epiglottitis and mucosal swelling. It can also be used to assess vocal cord mobility. Before securing nasal intubation, maxillary sinusitis or basal skull fractures should be ruled out. Maxillary sinusitis can be diagnosed by US. Boundaries of the maxillary sinus are orbital floor superiorly, hard palate inferiorly, nasal wall medially, and zygoma laterally. Sinus is normally air filled and thus impairs ultrasonic beam transmission. Only the anterior wall is seen with some artifact (acoustic shadowing), which obscures all of the underlying structures. If the sinus is filled with fluid, the ultrasonic beam will travel through the fluid after penetrating the anterior wall and gets reflected by the posterior or lateral walls producing an image known as "sinusogram." In the case of air-fluid level in the sinus or mucosal thickening, partial sinusogram (only posterior wall or side wall seen) is seen. For this, patient should be in upright position or semi-recumbent position so that fluid (if present) flows according to gravity covering the floor of the sinus and coming in contact with anterior wall.

### **6.11 Ultrasound-assisted percutaneous dilatational tracheostomy**

Many serious complications of percutaneous dilational tracheostomy like hemorrhage, high mediastinal vessels erosion, tracheal stenosis, esophageal disruption, and thyroid isthmus injury can be avoided by precise identification of anterior neck structures with the help of US [16]. Before attempting this, the neck should be examined for a midline trachea, the level of the tracheal ring, thyroid isthmus, vulnerable thyroid vessels, and diameter and the midline location of anterior jugular veins or other aberrant vasculature [18]. With advanced US technology, it will be possible in the future to have the real-time guidance in the placement of dilators and tracheostomy tubes.
