Point-of-care ultrasound is increasingly used at the bedside to integrate the clinical assessment of the critically ill; in particular, lung ultrasound has greatly developed in the last decade. This review describes basic lung ultrasound signs and focuses on their applications in critical care. Lung semiotics are composed of artifacts (derived by air/tissue interface) and real images (i.e., effusions and consolidations), both providing significant information to identify the main acute respiratory disorders. Lung ultrasound signs, either alone or combined with other point-of-care ultrasound techniques, are helpful in the diagnostic approach to patients with acute respiratory failure, circulatory shock, or cardiac arrest. Moreover, a semiquantification of lung aeration can be performed at the bedside and used in mechanically ventilated patients to guide positive end-expiratory pressure setting, assess the efficacy of treatments, monitor the evolution of the respiratory disorder, and help the weaning process. Finally, lung ultrasound can be used for early detection and management of respiratory complications under mechanical ventilation, such as pneumothorax, ventilator-associated pneumonia, atelectasis, and pleural effusions. Lung ultrasound is a useful diagnostic and monitoring tool that might in the near future become part of the basic knowledge of physicians caring for the critically ill patient.
Keywords: acute respiratory failure; lung monitoring; mechanical ventilation; thoracic ultrasound.