What is new in critical illness and injury science? Lung ultrasound assessment of disease severity and prognosis in patients with acute respiratory distress syndrome

Bedside thoracic or lung ultrasound (LUS) is often used to facilitate diagnosis and guide clinical management in critically ill patients with acute respiratory failure (ARF). LUS can be completed in any position (i.e., supine, semi-recumbent, lateral decubitus, and seated) as long as gravitational effects on pleuropulmonary processes are accounted for. Transducers with frequency ranges of 3.5–5.0 MHz are typically used for adequate lung penetration.[1] Higher frequency transducers in the ranges of 5–17 MHz can be used for detailed examination of the chest wall, underlying pleural surface, and diaphragm in the apposition zone.[1] LUS relies on the identification of findings (e.g., pleural effusion and parenchymal condensation) and artifacts (e.g., A-line, B-line, lung sliding, and lung point) which can be combined.[2] Of note, B-lines result from the widening of the pulmonary interlobular septa by either fluid accumulation (water and lymphatic fluid) from hydrostatic pressure or capillary permeability, excess extracellular matrix in fibrotic lung disease, excess inflammatory cells in early pneumonia, or carcinomatous cells.[1,3] When ultrasound waves meet the subpleural end of a thickened septum, an artifact called a B-line is created.[1,3] B-lines are discrete vertical, laser-like hyperechoic lines that originate from the pleura and move with respiration. Up to two B-lines per scanning plane may be seen in normal lung, while three or more B-lines in a longitudinal scanning plane between two ribs define a positive region. Two or more positive regions bilaterally constitute a positive examination and are termed a B-pattern, also known as an alveolar or pulmonary interstitial syndrome.[1,3] Among the most widely studied and utilized protocols for LUS is the bedside lung ultrasonography in emergency protocol, in which four points are assessed on each hemithorax.[4] Point 1 is located on the mid-clavicular line, at the second intercostal space, Point 2 is located on the anterior axillary line, at the fifth intercostal space; Point 3 is located along the diaphragm, at the mid-axillary line; and Point 4 (known as the posterolateral alveolar pleural syndrome point) is located on the most posterior point along the diaphragm, where the transducer is tilted anteriorly. When combined with venous analysis (when required), seven profiles are generated, yielding a 90.5% diagnostic accuracy.[4] Although considerable evidence has focused on the diagnostic performance of LUS and its utility to distinguish between causes of ARF, there remains a need to quantify the influence of LUS on clinical decision-making and patient-centered outcomes in acute respiratory distress syndrome (ARDS). When employed in the emergency department, a study by Seyedhosseini et al. reported no statistically significant decrease in hospital length of stay or patient mortality.[5] When employed in the intensive care unit, LUS has been reported to provide information that directly changed management in 47% of cases,[6] and has been reported to shorten the time to preliminary diagnosis, time to final diagnosis, time to treatment response, time to X-ray/computed tomography examination, and higher diagnostic accuracy.[7] In the current issue of the International Journal of Critical Illness and Injury Science, Sulgana et al. report the results of a prospective single-center observational study evaluating LUS in ARDS subjects with and without COVID-19.[8] The authors assess the correlation of LUS findings with disease severity and prognosis, by correlating its score with the three commonly used clinical severity scoring systems including sequential organ failure assessment score, acute physiology, and chronic health evaluation II score, simplified acute physiology score II, and mortality.[8] Sulgana et al. reported a significant positive correlation between LUS and all three severity scores, as well as their corresponding estimated mortality percentages. Although further prospective investigation is needed to confirm and further characterize these findings, the current available evidence suggests that the utility of LUS may extend beyond diagnostic to prognostic in the setting of ARDS. Research quality and ethics statement This report was exempt from the requirement of approval from the Institutional Review Board/Ethics Committee. The authors followed applicable EQUATOR Network (http://www.equator-network.org/) guidelines, however, no specific guideline is available for editorials.