Ultrasound lung comets or B lines in pulmonary edema – Cardiology Basics

Ultrasound lung comets or B lines in pulmonary edema – Cardiology Basics

Usually air in the lungs does not permit transmission of ultrasound and that is the reason for poor echo window in those with chronic obstructive airways disease. But when the lung is waterlogged in pulmonary edema, certain broad lines extending from the transducer location to the end of the imaging field appear on lung ultrasound. These have been called as B lines or ultrasound lung comets. They move with the lung movement in respiration. B lines are easy to detect with any ultrasound device including pocket devices and conventional echocardiographs. Hence detection of B lines is being widely used in the emergency departments.

B lines can also occur in pulmonary fibrosis with some differences. Cardiogenic B lines are always bilateral and generally more diffuse on the right lung than on the left. They are more in the axillary regions in supine patients, being dependent regions. Cardiogenic B lines disappear within hours of intravenous diuretic treatment [1]. B lines in pulmonary fibrosis are often associated with pleural thickening [2].

Differentiation of cardiogenic from non-cardiogenic pulmonary edema due to acute respiratory distress syndrome (ARDS) is another challenge often faced in the emergency department and intensive care setting. Clinical scenario and other findings of cardiac involvement are useful in differentiation. Some findings on lung ultrasound may also be useful. Abnormalities in the pleural line due to small subpleural consolidations can occur in ARDS [3].

There can be spared areas in ARDS with normal sonographic appearance surrounded by areas of multiple B lines. Consolidations of various sizes can be present in ARDS, but not in pure cardiogenic pulmonary edema. Absence or reduction of pleural gliding may also be noted in ARDS. Pleural line being superficial, is better evaluated using a linear, high frequency probe and not the conventional sector probe used for echocardiography [3].

References

1. Volpicelli G, Caramello V, Cardinale L, Mussa A, Bar F, Frascisco MF. Bedside ultrasound of the lung for the monitoring of acute decompensated heart failure. Am J Emerg Med. 2008 Jun;26(5):585-91. doi: 10.1016/j.ajem.2007.09.014. PMID: 18534289.
2. Gargani L. Lung ultrasound: a new tool for the cardiologist. Cardiovasc Ultrasound. 2011 Feb 27;9:6. doi: 10.1186/1476-7120-9-6. PMID: 21352576; PMCID: PMC3059291.
3. Copetti R, Soldati G, Copetti P. Chest sonography: a useful tool to differentiate acute cardiogenic pulmonary edema from acute respiratory distress syndrome. Cardiovasc Ultrasound. 2008 Apr 29;6:16. doi: 10.1186/1476-7120-6-16. PMID: 18442425; PMCID: PMC2386861.