Aerated lungs often interfere with sonographic visualization of the organs deep to them, such as often occurs in cardiac and biliary exams. This is due to the scattering effect of gas molecules on the ultrasound beam. For this reason, ultrasound of the lungs themselves was long thought to be of no diagnostic use. However, in recent years, researchers and clinicians have discovered that lung ultrasound can be used to assess for pathologic conditions that occur at the interface of the lung and the chest wall such as pneumothorax, pulmonary edema, and pneumonia. The evaluation of the pleura and the finding of lung sliding to evaluate for pneumothorax was described earlier in the section on trauma ultrasound. Contemporary point-of-care lung ultrasound often evaluates for the presence of alveolar interstitial syndrome, which occurs with the collection of fluid within the interlobular and intralobular lymphatics of the lung. This occurs in various pathologic states including cardiogenic pulmonary edema, acute respiratory distress syndrome, pneumonia, and diffuse parenchymal lung disease. Lung ultrasound can also effectively be used to visualize lung consolidation and pleural effusions.
Lung Zones. Current consensus recommendations include scanning the thorax in eight separate zones including the costophrenic angles of each chest. (Illustration contributor: Robinson M. Ferre, MD.)
A more focused lung exam can be performed depending on the pathology suspected. For example, if assessing for a pneumothorax following a subclavian central venous line, anterior views along the midclavicular line would be sufficient.
Convex array (anterior and costophrenic angles)
Phased array (costophrenic angles; poor for assessing lung sliding)
Linear array (anterior chest only)
The patient is traditionally imaged in a supine position, which is necessary if assessing for a pneumothorax.
If assessing for conditions other than pneumothorax, a supine, semi-recumbent, or upright position may be used.
To assess for alveolar interstitial syndrome or consolidation: With the indicator pointed toward the patient’s head, each of the four zones of each hemithorax should be imaged. The depth on the screen should be between 13 and 15 cm deep. Each zone should be imaged thoroughly for evidence of A-lines, B-lines, or consolidation.
To assess for pleural fluid: The technique for evaluating costophrenic angles for pleural effusion is identical to that employed in the E-FAST when evaluating for hemothorax.
To assess for ...