The lungs were traditionally considered poorly accessible to ultrasound, as ultrasound waves cannot penetrate air-filled structures; however, lung POCUS relies on the interpretation of patterns of artifacts to evaluate the normal, air-filled lungs.
When there is lung pathology, the consolidation or fluid allows for direct visualization of the pathology with lung POCUS and replaces the air artifacts. Fluid in a consolidation or effusion is easily visualized with ultrasound if the fluid has direct contact with the pleural surface. As lung POCUS will only visualize the lung under the probe, it is essential to completely evaluate the lungs anteriorly, laterally, and posteriorly to avoid missing pathology.
Positioning and Probe
- The patient should be in a position of comfort: supine, sitting, or in parent’s lap (Figure 1).
- Warm gel helps with the child’s comfort.
- Distractions such as a toy, book, or phone/tablet can also help ease anxiety.
- Use a linear high frequency probe. If increased depth is needed, such as in the evaluation for effusion, a curvilinear or phased array probe may also be used.
There are different protocols to scan the lung depending on the purpose of the evaluation. For example, in pneumothorax, we focus on the anterior chest where air rises in a supine patient, and for the extended Focused Assessment with Sonography (eFAST) exam, we focus on more dependent areas where pleural fluid or blood collects. Below we discuss the complete lung exam which is often used in evaluating for pneumonia.
- A 6-zone lung ultrasound protocol is used for a complete lung examination (Figure 2):
- Anterior lungs bilaterally are scanned in the mid-clavicular line from the apex to the base of the lungs and diaphragm.
- Lateral lungs bilaterally are scanned in the mid-axillary line from the apex to the base of the lungs and diaphragm.
- Posterior lungs bilaterally are scanned medial to the scapulae and lateral to the vertebral bodies from the apex to the base of the lungs and diaphragm.
- Place the probe longitudinally, perpendicular to the ribs, with the probe marker towards the patient’s head. Identify anatomical landmarks on ultrasound (Figure 3, Video 1).
Video 1: Normal lung POCUS in longitudinal orientation
Video 2: Normal lung POCUS in transverse orientation
Normal Lung Findings
- Ribs: Hyperechoic, curvilinear structure with posterior acoustic shadowing
- Pleural line: Hyperechoic line immediately deep to the ribs
- Lung sliding sign: Visceral and parietal pleural are juxtaposed and sliding against each other with respirations, giving the pleural line a shimmering or “ants marching on a log” appearance. For additional examples, see the PEM POCUS Endotracheal Intubation Confirmation article, specifically in Section 2 – Indirect Confirmation: Visualize Bilateral Lung Sliding.
- Lungs filled with air: Visualized on POCUS as horizontal A-lines, which are a reverberation artifact of the pleural line. The pleural line is reflected as the ultrasound beams bounce back and forth between the probe and the highly reflective pleural line, and therefore the distance between A-lines is the same as the distance between the probe and the pleural line (Figure 4).