The dynamic sonographic air bronchogram: a simple and immediate bedside diagnosis of alveolar consolidation in severe respiratory failure.

R failure is one of the most common life-threatening conditions in critical care. Adjuncts such as physical examination and portable x-ray imaging may be insensitive and misleading in the critically ill. Computed tomography is accurate but invokes risks including patient transfer, exposure to radiation, and increased cost. Ultrasound is increasing in popularity as an extension of the physical examination. The dynamic air bronchogram sign was first described in 2002 by Dr. Lichtenstein of Paris.1 The dynamic air bronchogram itself consists of numerous punctiform or linear hyperechoic opacities that move with the respiratory cycle. The hyperechoic areas are generated by the aerated bronchi that have a much higher acoustic reflectance than the surrounding consolidated pulmonary parenchyma, which has a similar density as water.2 The presence of this sign suggests that the lung, which is generally sono-occult except at the pleural surface, has been transformed into an organ with a similar density as the liver (sonographic hepatization of the lung). Further, the recognition of air artifacts within the lung parenchyma delineates the bronchial tree: a fact corroborated by the movement of the artifacts with ventilation. The fact that the air bronchograms are dynamic rather than static infer that the major airways are open and not obstructed: a situation more likely to produce static air bronchograms.2 In one study, the dynamic air bronchogram was present in 32 of 33 patients admitted with acute pneumonia.3 In our case, a 73-year-old man was admitted to the intensive care unit with fever, dyspnea, profound hypoxemia, and shock. A bedside ultrasound examination was performed with a Sonosite MicroMaxx portable US system (Sonosite Corporation, Bothell, WA). This examination demonstrated that the right lower lobe was completely consolidated (Fig. 1). These features are best demonstrated on video (see Video, Supplemental Digital Content 1, which demonstrates a consolidated lung to the left of the diaphragm with the liver to the right of the diaphragm, http://links.lww.com/TA/A21). A closer look at the ultrasound images revealed multiple dynamic air bronchograms (Fig. 2). Again, these features are best seen on video imaging (see Video, Supplemental Digital Content 2, which demonstrates multiple linear hyperechoic areas (arrows) corresponding to intrabronchial air densities, which are seen within the substance of the consolidated lung parenchyma, http://links.lww. com/A22). With eventual recovery, these signs remitted and were replaced with the expected “normal” thoracic sonographic findings (Fig. 3; see Video, Supplemental Digital Content 3, which demonstrates that the hepatization of the lung has resolved and the dynamic air bronchogram sign has disappeared, http://links.lww.com/A23). Clinicians using bedside pulmonary ultrasound to rapidly assess their sickest patients should be familiar with these findings and their implications as it may decrease time to diagnosis, limit unnecessary procedures, reduce risky patient transfers, limit a patient’s exposure to ionizing radiation, and guide patient care.