Identification of Sonographic B-lines with Linear Transducer Predicts Elevated B-Type Natriuretic Peptide Level

This study sought to correlate the presence of pleural-based B-lines seen by emergency department ultrasound performed with the linear transducer with B-type natriuretic peptide (BNP) level in patients with suspected congestive heart failure.

The study was a prospective convenience sample on adult patients in an academic, urban emergency department with over 100,000 annual patient visits. Adult patients with a BNP level ordered by the treating physician were prospectively enrolled by one of four physicians, blinded to the BNP level. The enrolling physicians included an emergency ultrasound director, two emergency ultrasound fellows, and a senior emergency medicine resident. Bedside ultrasound was performed using a 3-12 MHz linear broadband transducer in four lung fields. The serum BNP level was correlated with bilateral B-lines, defined as three or more comet-tail artifacts arising from the pleural line extending to the far field without a decrease in intensity on the right and left thorax.

Sixty three patients were consented and enrolled during a four-month period. Fifteen patients had the presence of bilateral B-lines. The median BNP in patients with bilateral B-lines was 1560 pg/mL (95% confidence interval (CI) 1141-3706 pg/mL), compared with 538 pg/mL (95% confidence interval 310-1917 pg/mL) in patients without B-lines. The distributions in the two groups differed significantly (p=0.0006). Based on the threshold level of BNP 500 pg/mL, the sensitivity of finding bilateral B-lines on ultrasound was 33.3% (95% CI: 0.19-0.50), and the specificity was 91.7% (95% CI: 0.73-0.99). In addition, bilateral B-lines were absent in all patients with a BNP<100 pg/mL.

The presence of bilateral B-lines identified with the linear probe is associated with significantly higher BNP levels than patients without B-lines. In our patient population, the presence of B-lines was specific but not sensitive for BNP>500. Further research may show that it can be applied to quickly assess patients with undifferentiated dyspnea.