Prognostic value of extravascular lung water assessed with ultrasound lung comets by chest sonography in patients with dyspnea and/or chest pain

We thank Dr Volpicelli for his interest in our article. The letter raises several interesting issues deserving clarification. 1.The semantics. It is true that other names have been proposed over the years, such as “comet-tail artifacts” or “B-lines” in the seminal work of Lichtenstein et al. 1 Lichtenstein D. Meziere G. Biderman P. Gepner A. Barre O. The comet-tail artifact. An ultrasound sign of alveolar-interstitial syndrome. Am J Respir Crit Care Med. 1997; 156: 1640-1646 Crossref PubMed Scopus (820) Google Scholar We prefer ultrasound lung comets (ULCs) because the acronym puts together several key information necessary to establish a clear “relation between signs and the things they refer to” (Wikipedia definition of semantics). The term “ultrasound lung comet” implies ultrasound-based technique, lung sonography, and comet-like appearance. 2 Picano E. Frassi F. Agricola E. Gligorova S. Gargani L. Mottola G. Ultrasound lung comets: a clinically useful sign of extravascular lung water. J Am Soc Echocardiogr. 2006; 19: 356-363 Abstract Full Text Full Text PDF PubMed Scopus (356) Google Scholar The term “artifact” may be misleading, because the first echo of the comet reverberation is indeed generated by a real biological interface in the water-thickened subpleural interlobular septa. The term “B-line” is also unsatisfactory because ULCs can be present before Kerley B-lines and can be made of water but also of connective tissue. 2.The diagnostic ambiguity. ULCs can be present for accumulation of lung water (eg, in heart failure) or lung fibrosis (eg, in diffuse sclerodermia). Dr Volpicelli points out that in patients with acute dyspnea, no ULCs are usually detected in pneumogenic dyspnea. We agree on that, and indeed we have shown that ULCs can help the cardiologist in identifying cardiogenic dyspnea. 3 Gargani L. Frassi F. Soldati G. Tesorio P. Gheorghiade M. Picano E. Ultrasound lung comets for the differential diagnosis of acute cardiogenic dyspnoea: a comparison with natriuretic peptides. Eur J Heart Fail. 2008; 10: 70-77 Crossref PubMed Scopus (207) Google Scholar 3.The prognostic meaning. We agree that ULCs can help the physician to monitor the diuretic efficacy in patients with pulmonary congestion at the bedside, but in our opinion it seems unlikely that the worse prognosis is only linked to the resistance and delay in the clearing up of ULCs by treatment. Both watery and fibrotic ULCs probably have an unfavorable prognostic meaning, and it is entirely possible that “fixed” (fibrotic, diuretic-resistant) ULCs are prognostically different from “reversible” (watery) ULCs. Neverthless, it is well known that in patients with heart failure or acutely ill patients, lung water accumulation is associated with a worse prognostic outcome. 4 National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network Wiedemann H.P. Wheeler A.P. Bernard G.R. Thompson B.T. Hayden D. deBoisblanc B. et al. Comparison of two fluid-management strategies in acute lung injury. N Engl J Med. 2006; 354: 2564-2575 Crossref PubMed Scopus (2795) Google Scholar 4.The quantification. The ULC score adopted in our laboratory 2 Picano E. Frassi F. Agricola E. Gligorova S. Gargani L. Mottola G. Ultrasound lung comets: a clinically useful sign of extravascular lung water. J Am Soc Echocardiogr. 2006; 19: 356-363 Abstract Full Text Full Text PDF PubMed Scopus (356) Google Scholar integrates the number of ULCs in any intercostal space (the severity) with the number of intercostal spaces showing an abnormal signal (the extent). This method served us well in clinical 3 Gargani L. Frassi F. Soldati G. Tesorio P. Gheorghiade M. Picano E. Ultrasound lung comets for the differential diagnosis of acute cardiogenic dyspnoea: a comparison with natriuretic peptides. Eur J Heart Fail. 2008; 10: 70-77 Crossref PubMed Scopus (207) Google Scholar and experimental studies 5 Gargani L. Lionetti V. Di Cristofano C. Bevilacqua G. Recchia F.A. Picano E. Early detection of acute lung injury uncoupled to hypoxemia in pigs using ultrasound lung comets. Crit Care Med. 2007; 35: 2769-2774 Crossref PubMed Scopus (132) Google Scholar over the years, and it seems to be an acceptable trade-off between need of accuracy and priority of simplicity. 2 Picano E. Frassi F. Agricola E. Gligorova S. Gargani L. Mottola G. Ultrasound lung comets: a clinically useful sign of extravascular lung water. J Am Soc Echocardiogr. 2006; 19: 356-363 Abstract Full Text Full Text PDF PubMed Scopus (356) Google Scholar This approach is easy to do and fast to learn. 6 Bedetti G. Gargani L. Corbisiero A. Frassi F. Poggianti E. Mottola G. Evaluation of ultrasound lung comets by hand-held echocardiography. Cardiovasc Ultrasound. 2006; 4: 34 Crossref PubMed Scopus (174) Google Scholar We count ULCs on-line during the examination, on moving images, and the image freeze is rarely used. Several other approaches are obviously possible. 5.The pragmatics. Pragmatics is an important part of semeiotics and describes the relation of signs to their impact on those who use them (Wikipedia). We need quantification for accuracy, but we also need simplicity for a clinically driven assessment in a theatre often characterized by intense time pressure. In this context, the separation of “black,” “black and white,” and “white” lung is an attempt to broadly simplify the main, clinically relevant patterns of chest sonography for the cardiologist. In the lungs, the normal signal is no signal, and the abnormal signal represents “the shape of water” and can be semiquantitatively titrated by eyeballing analysis. Dr Volpicelli himself seems to be vulnerable to the appeal of this straightforward approach because he elegantly describes “shining” or “white” lung comets a few lines before warning against the use of this terminology “disconcerting for the sonographer.” When a “white lung” pattern is observed in a given intercostal space, we assign the arbitrary “plateau” value of 10 ULCs for quantification purposes.