**6.6 Ultrasound-guided airway blocks to facilitate awake intubation**

For performing upper airway blocks in fiberoptic bronchoscopy, US plays an important role. It helps to identify superior laryngeal nerve (SLN) for SLN block. SLN running between thyroid cartilage and hyoid bone can be easily seen on transverse US

## **Figure 2.**

*Measurement of laryngeal air column (US probe placed transverse across the trachea). The length of the blue dashed/discontinuous line is the width of the air column (image credits: Author Dr Venkata Ganesh).*

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

#### **Figure 3.**

*With the US probe placed in the transverse plane and scanning cephalocaudally, the topmost image shows the thyroid cartilage (magenta) followed caudally by the cricothyroid membrane (red), cricoid (dark blue), and the trachea (yellow). (image credits: Author Dr Venkata Ganesh).*

at hyoid bone level. The membrane between the thyroid cartilage and hyoid bone is an iso-echoic line from both sides of the hyoid bone with hyperechoic air below [16].

#### **6.7 Ultrasound-guided intubation**

Endotracheal intubation is conventionally confirmed by capnography, five point chest auscultation, and esophageal intubating devices. US-guided equal movement

#### **Figure 4.**

*String of pearls appearance (US probe placed in the saggital plane). Magenta—thyroid cartilage; red cricothyroid membrane; dark blue—cricoid; yellow—trachea. (image credits: Author Dr Venkata Ganesh).*

of bilateral pleura and diaphragm indicating expansion of lungs is an indirect sign of correct physiological function of the tracheal tube in mechanically ventilated patients. Lung sliding sign seen on intercostal US view at interface of lung-chest wall also indicates lung expansion.

Esophageal intubation can be identified if the esophagus is lateral to the trachea (**Figure 5**). When intubating under real-time ultrasound guidance, the lack of a disruption in the tracheal air column with a noticeable movement in the esophagus can detect esophageal intubations earlier than capnography or auscultation [17] *(image credits: Author Dr Venkata Ganesh).*

Esophageal intubation results in a paradoxical or immobile state of the diaphragm. Esophageal intubation causes paradoxical ventilation where the diaphragm moves toward the chest due to raised intra-abdominal pressure caused by stomach distension by positive pressure ventilation.

US can also be used to diagnose endobronchial intubation by assessing the diaphragm movement and lung-slide sign on the ventilated lung side (endobronchial) and absent or restricted diaphragm movement and absent lung-slide sign on the non-ventilated lung side [13].

Normal pediatric airway can be visualized in real time using US during tracheal intubation by assessing 1) trachea and tracheal rings identification, 2) vocal cords visualization, 3) widening of glottis with passage of ETT, and 4) confirmation of ETT position above the carina and visualization of sliding sign after manual lung ventilation.
