chest wall and immediately deep to the ribs Normal lung sliding occurs as the visceral pleura glides back and forth over the parietal pleura ( Video 131.11 ) On dynamic ultrasound imaging this appears as a slight movement or “sparkling” pattern of the hyperechoic pleural line that varies with the respiratory cycle On M-mode, normal lung sliding generates what is referred to as the “seashore sign” where the top of the image (representing the nonmoving chest wall) appears as horizontal lines, or the “waves,” and the bottom of the image (representing the aerated, expanded lung) appears as the “grains of sand” (Fig 131.12 A ) Technique Pediatric lung ultrasound is generally performed using a linear, high-frequency probe because this provides adequate depth and higher-quality image resolution than a convex, low-frequency probe Patient positioning will depend on the clinical scenario—patients who are critically ill can be examined in the supine position, while those who are more stable can be placed in the seated position In addition, certain findings will be more easily seen with different patient positioning For example, pneumothorax will be more easily detected in the anterior lung fields of a supine patient, while pleural effusions will be better visualized in the lower lung fields of a seated patient Starting in the longitudinal view with the probe marker pointing toward the patient’s head, the lung can be scanned sequentially in all areas of the thorax or, alternatively, a more targeted assessment can be performed Pneumothorax will appear as the absence of lung sliding ( Videos 131.11 [normal] and 131.12 [pneumothorax]) On M-mode, this will appear as the “stratosphere” or “barcode” sign, with the entire image showing no movement and thus appearing as horizontal lines all the way down (Fig 131.12 B ) Pleural effusions, which can generally first be seen in the posterior costophrenic sulcus, appear as an anechoic fluid layer overlying the pulmonary parenchyma Transudate and hemothorax may appear as simple, anechoic fluid ( Video 131.13 ) while an empyema can have internal septations or organized fibers ( Video 131.14 )