Page 46 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

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Chapter 2
A pneumothorax is characterized by the abolition of lung sliding, the absence of B-lines and the appearance of the A-line sign.39 Lung sliding is the representation of the visceral and parietal pleura sliding against each other during respiration. B-lines are the result of the accumulation of fluid in the pulmonary interstitium. Therefore, the presence of B-lines on PoCUS rules out a pneumothorax. Horizontal A-lines are reflections of the pleural line caused by gas below the parietal pleura either within or outside of the lung. These signs are explained further in Table 2 1; adapted from Lichtenstein’s paper on the BLUE and FALLS protocol.39 A normal lung US image is shown in Figure 2.1, Figure 2.2, and Figure 2.3. Images of pneumothorax are shown in Figure 2.4, Figure 2.5, and Video 2.1.
An important implication of detecting or excluding pneumothorax is the subsequent deci- sion to perform (or withhold) a tube thoracostomy. An evaluation of prehospital chest US in 281 patients revealed that the acute medical management changed in 21%. The intention to introduce a tube thoracostomy was abandoned in 4% (n = 10) and the transport destina- tion changed in another 4%.4 Similarly, Mazur found that chest US examinations (n = 60) performed in preparation for air transport helped them prevent four (8%) chest tube tho- racostomies.47
Figure 2.3 Normal lung – M-mode ultrasound image
The ultrasound reflections on the vertical line in the upper part of the image are sequentially displayed from left to right in the lower part as time progresses. It allows to capture the motion of the upper 2D image in the station- ary image below.
A normal M-mode image of the chest wall and pleura is displayed here. The stationary chest wall produces straight horizontal lines above the pleural line. The lung sliding and movement of the artifacts below produces a grainy image. This is called the seashore sign.