Lung Ultrasound in Critical Care and Emergency Medicine: Clinical Review

Abstract

Lung ultrasound has become a part of the daily examination of physicians working in intensive, sub-intensive, and general medical wards. The easy access to hand-held ultrasound machines in wards where they were not available in the past facilitated the widespread use of ultrasound, both for clinical examination and as a guide to procedures; among point-of-care ultrasound techniques, the lung ultrasound saw the greatest spread in the last decade. The COVID-19 pandemic has given a boost to the use of ultrasound since it allows to obtain a wide range of clinical information with a bedside, not harmful, repeatable examination that is reliable. This led to the remarkable growth of publications on lung ultrasounds. The first part of this narrative review aims to discuss basic aspects of lung ultrasounds, from the machine setting, probe choice, and standard examination to signs and semiotics for qualitative and quantitative lung ultrasound interpretation. The second part focuses on how to use lung ultrasound to answer specific clinical questions in critical care units and in emergency departments.

Keywords: acute respiratory failure; lung aeration; lung ultrasound; pleural effusion; pneumonia; pneumothorax; point-of-care ultrasound.

Figure 1

The figure illustrates both approaches to lung ultrasound: the longitudinal approach (A–C) and the transversal approach (D–F). In the longitudinal approach, the probe is aligned to the craniocaudal axis of the patient and perpendicular to the ribs’ axis (A,B), giving the characteristic ultrasonographic image of the two ribs and their shadows defining the pleural line in the middle, the so-called bat sign (C); in the transversal approach the probe is placed in the intercostal spaces, parallel to the ribs’ axis (D,F), so that a larger pleural section can be displayed without any rib’s shadows visualized (F).

Figure 2

The illustration shows the six-areas division of a hemithorax in a supine patient for a comprehensive lung ultrasound examination. The anterior and the posterior axillary lines divide the hemithorax into three parts, which are finally divided into superior and inferior. The areas may be numbered from “1” to “6”, corresponding, respectively, to the anterior–superior and the inferior–posterior areas. (A) Zone 1 and 2 are superior and inferior anterior scans, zone 3 and 4 are superior and inferior lateral scans; (B) Zone 5 and 6 are superior and inferior posterior scans.

Figure 3

The lung ultrasound score is represented in the illustration above. Score 0 corresponds to the visualization of the A-lines only or with less than three B-lines per scan; score 1 is given if three or more well defined B-lines or coalescent B-lines/sub-pleural consolidations are visualized but they cover < 50% of the inspected zone; score 2 corresponds to the presence of multiple B-lines (coalescent or not) or sub-pleural consolidations occupying > 50% of the visualized pleura; score 3 is finally assigned when a clear tissue-like pattern is observed.

Figure 4

Flow-chart to rule in or rule out a pneumothorax. Scanning the anterior zones, detection of B-lines, real images, lung sliding, or lung pulse have to be found to rule out a pneumothorax. The only sign that could rule in pneumothorax is the lung point, and to find it, it may be necessary to extend the research to the lateral zones. PTX = Pneumothorax.

Figure 5

A brief practical ultrasonographic diagnostic approach to the hypoxemic patient, starting from the visualization of A-lines and B-lines in the anterior areas and, thereafter, evaluating other more specific signs and the posterolateral zones. ARDS = Acute Respiratory Distress Syndrome; COPD = Chronic Obstructive Pulmonary Disease; CPE = Cardiac Pulmonary Edema; DVT = Deep Venous Thrombosis; MV = Mechanically Ventilated; PEEP = Post End Expiratory Pressure; RV = Right Ventricle.

Figure 6

A decisional approach to pulmonary consolidations in intubated patients. BAL = Bronchoalveolar lavage; FBS = Fiber-bronchoscopy; MV = Mechanically Ventilated; VAP = Ventilator Associated Pneumonia.

Figure 7

A brief flow-chart to predict patient’s responsiveness to PEEP or prone position. LUS = Lung Ultrasound; MV = Mechanically Ventilated; PEEP = Positive End Expiratory Pressure.

Figure 8

A graphic representation of four level steps of skills-knowledges based on the expertise of the physician performing lung ultrasound. ARF = Acute Respiratory Failure; LUS = Lung Ultrasound; MV = Mechanical Ventilation; VPLUS = ventilator-associated pneumonia lung ultrasound score.