B‐Lines for the assessment of extravascular lung water: Just focused or semi‐quantitative?

Background B‐lines as typical artefacts of lung ultrasound are considered as surrogate measurement for extravascular lung water. However, B‐lines develop in the sub‐pleural space and do not allow assessment of the whole lung. Here, we present data from the first observational multi‐centre study focusing on the correlation between a B‐lines score and extravascular lung water in critically ill patients suffering from a variety of diseases. Patients and Methods In 184 adult patients, 443 measurements were obtained. B‐lines were counted and expressed in a score which was compared to extravascular lung water, measured by single‐indicator transpulmonary thermodilution. Appropriate correlation coefficients were calculated and receiver operating characteristics (ROC‐) curves were plotted. Results Overall, B‐lines score was correlated with body weight‐indexed extravascular lung water characterized by r  = .59. The subgroup analysis revealed a correlation coefficient in patients without an infection of r  = .44, in those with a pulmonary infection of r  = .75 and in those with an abdominal infection of r  = .23, respectively. Using ROC‐analysis the sensitivity and specificity of B‐lines for detecting an increased extravascular lung water (>10 mL/kg) was 63% and 79%, respectively. In patients with a P/F ratio <200 mm Hg, sensitivity and specificity to predict an increased extravascular lung water was 71% and 93%, respectively. Conclusions Assessment of B‐lines does not accurately reflect actual extravascular lung water. In presence of an impaired oxygenation, B‐lines may reliably indicate increased extravascular lung water as cause of the oxygenation disorders.