Inter-Rater Reliability of Quantifying Pleural B-Lines Using Multiple Counting Methods

OBJECTIVES: Sonographic B-lines are a sign of increased extravascular lung water. Several techniques for quantifying B-lines within individual rib spaces have been described, as well as different methods for "scoring" the cumulative B-line counts over the entire thorax. The interobserver reliability of these methods is unknown. This study examined 3 methods of quantifying B-lines for inter-rater reliability. METHODS: Videotaped pleural assessments of adult patients presenting to the emergency department with dyspnea and suspected acute heart failure were reviewed by 3 blinded pairs of emergency physicians. Each pair performed B-line counts within single rib spaces using 1 of the following 3 predetermined methods: 1, individual B-lines are counted over an entire respiratory cycle; 2, as per method 1, but confluent B-lines are counted as multiple based on the percentage of the rib space they occupy; and 3, as per method 2, but the count is made at the moment when the most B-lines are seen, not over an entire respiratory cycle. A single-measures interclass correlation coefficient was used to assess inter-rater reliability for the 3 definitions of B-line counts. RESULTS: A total of 456 video clips were reviewed. The interclass correlation coefficients (95% confidence intervals) for methods 1, 2, and 3 were 0.84 (0.81-0.87), 0.87 (0.85-0.90), and 0.89 (0.87-0.91), respectively. The difference between methods 1 and 3 was significant (P = .003). CONCLUSIONS: All methods of B-line quantification showed substantial inter-rater agreement. Method 3 is more reliable than method 1. There were no other significant differences between the methods. We recommend the use of method 3 because it is technically simpler to perform and more reliable than method 1.