Be discussed in chapter 13 focused questions for

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be discussed in Chapter 13 . Focused questions for respiratory ultrasound The questions for airway ultrasound are as follows: 1. Where is the cricothyroid membrane? 2. Is the intubation successful? The questions for chest ultrasound are as follows: 1. Are A-lines present? 2. Are B-lines present? Diagnostic ultrasound 191 Respiratory ultrasound
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Anatomy Airway When using ultrasound to identify anatomy in the neck, it is important to start midline and to visualize the hyperechoic tracheal rings in both a longi- tudinal and a transverse plane ( Figure 9.1 ). The cricothyroid membrane can be seen in the longitudinal plane as the most superior dark space above the most proximal tracheal ring. Its appearance has been described as “sandwich- like,” as the dark spaces above and below the membrane are longer than those in between the bright dense cartilage of the tracheal rings ( Figure 9.2 ). Figure 9.2 Longitudinal view of the cricothyroid membrane. (A) (B) Figure 9.1 ( A ) Transverse and ( B ) longitudinal views of the trachea. 192 Diagnostic ultrasound Respiratory ultrasound
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In addition, by applying Doppler, the arteries and veins that supply the thyroid tissue can be identified. In emergency situations, seeing these vessels can help you avoid them. More importantly, an emergent cricothyr- otomy is attempted when swelling or hemorrhage in the neck distorts normal anatomy. Ultrasound can identify these fluid collections and help find the tracheal ring landmarks if they have been pushed from their normal anatomic position. Finally, the esophagus is usually visualized as a col- lapsed hyperdense structure just to the left of the trachea. The layers of esophageal mucosa can be seen to the right of the tracheal shadow in Figure 9.3 . If the probe is held transverse over the mid trachea, the reflective shadow of the endotracheal tube can be visualized passing through the trachea. If it is seen entering the esophagus laterally, this can be immedi- ately corrected without insufflation or other confirmatory testing required. Intubation can also be confirmed by correlating lung sliding to mechanical ventilation [ 2 ]. Normal bilateral lung sliding after intubation indicates cor- rect endotracheal tube placement. Chest When using ultrasound to make diagnoses in lung pathology, it is important to recall some of the basic principles described in Chapter 1 . One of the reasons that the normal lung is so difficult to image with ultrasound is that air is not a good transducer of sound waves. Air molecules tend to scatter sound waves in infinite directions, making it difficult for the transducer to receive any organized information from the returning sound wave. This property can actually be helpful in chest ultrasound, because a well-aerated and normal lung will not show much at all except for the horizontal reverber- ation artifact between the skin and the pleura that occurs when sound is Figure 9.3 View of the esophagus just lateral to the trachea (T).
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