B-lines are are an ultrasound resonance artefact that appears when there is a marked difference in acoustic impedance between an object and it´s surroundings.
On the screen it looks like a beam projecting from the pleura all the way to the edge of the screen. Lung water interfacing with air can be the source of the resonance and it is commonly seen i pulmonary oedema.
Three or more B-lines per field of scan with a distance between B-lines <7mm is considered indicative of pulmonary oedema. The present study tries to correlate B-profile on US with another marker of heart failure, pro-BNP which is produced by overstretched cardiomyocytes when left ventricle filling pressure is increased.
A-lines, on the other hand, indicate dry interlobar septa and is a normal finding. A-lines are a reverberation artefact of the pleura. On US they appear as one or more horisonal lines. Predominance of A lines is commonly suggestive of astma/COPD rather than oedema as the cause of dyspnoea.
A prospective study that included adult patients presenting to the ED with acute dyspnoea likely to be explained by pulmonary oedema and left ventricular failure. All patients had bilateral anterior and lateral lung ultrasound scan using a curvilinear probe. Images were stored and then reviewed by an independent ICU physiscian. Patients were based on US labelled B-line dominant profile or A-line dominant profile. Median Pro-BNP values were determined.
14 patients had an A-profile on lung US, 10 of which had a negative pro-BNP. Their median pro BNP was 180.
Take home message
The European Society of Cardiology recommends using natriuretic peptide to rule out acute heart failure with reasonably high sensitivity albeit with low specificity. The sensitivity and specificity for lung US in detecting elevated pro-BNP indicative of heart failure is 92% and 91%.
Study lives here (free!):
Ann Intensive Care. 2015 Dec;5(1):56. doi: 10.1186/s13613-015-0100-x. Epub 2015 Dec 30. Sonographic chest B-lines anticipate elevated B-type natriuretic peptide level, irrespective of ejection fraction. Bitar Z1, Maadarani O2, Almerri K3.
Acad Emerg Med. 2009 Mar;16(3):201-10. doi: 10.1111/j.1553-2712.2008.00347.x. Epub 2009 Jan 29. Emergency thoracic ultrasound in the differentiation of the etiology of shortness of breath (ETUDES): sonographic B-lines and N-terminal pro-brain-type natriuretic peptide in diagnosing congestive heart failure. Liteplo AS1, Marill KA, Villen T, Miller RM, Murray AF, Croft PE, Capp R, Noble VE.
West J Emerg Med. 2011 Feb;12(1):102-6. Identification of Sonographic B-lines with Linear Transducer Predicts Elevated B-Type Natriuretic Peptide Level. Manson WC1, Bonz JW, Carmody K, Osborne M, Moore CL.