Lung Ultrasound Imaging: A Primer for

Echocardiographers
Eugene Yuriditsky, MD, James M. Horowitz, MD, Nova L. Panebianco, MD, Harald Sauthoff, MD,
and Muhamed Saric, MD, PhD, New York, New York; and Philadelphia, Pennsylvania

Lung ultrasound (LUS) has gained considerable acceptance in emergency and critical care medicine but is yet
to be fully implemented in cardiology. Standard imaging protocols for LUS in acute care settings have allowed
the rapid and accurate diagnosis of dyspnea, respiratory failure, and shock. LUS is greatly additive to echo-
cardiography and is superior to auscultation and chest radiography, particularly when the diagnosis of acute
decompensated heart failure is in question. In this review, the authors describe LUS techniques, interpretation,
and clinical applications, with the goal of informing cardiologists on the imaging modality. Additionally, the au-
thors review LUS findings associated with various disease states most relevant to cardiac care. Although there
is extensive literature on LUS in the acute care setting, there is a dearth of reviews directly focused for prac-
ticing cardiologists. Current evidence demonstrates that this modality is an important adjunct to echocardiog-
raphy, providing valuable clinical information at the bedside. (J Am Soc Echocardiogr 2021;-:---.)

Keywords: Lung ultrasound, Heart failure, Point-of-care ultrasound

Historically, aerated lungs and the bony thorax have been viewed as the standard of care for critically ill patients.3,8-10 Additionally,
barriers to sonographic evaluation. However, altered pleural and unlike radiography and CT, LUS involves no ionizing radiation and
parenchymal tissue characteristics produce specific artifacts that can can be repeated without additional risk to the patient.
be used to aid in diagnosis of lung pathologies.1-3 Normal, aerated Although some published literature on LUS exists in cardiology
lung is characterized by very different acoustic impedance journals, cardiologists are yet to fully apply this imaging modality in
compared with the chest wall, resulting in near complete reflection daily practice.4,8,11 LUS is thought to be a fairly simple skill with quick
of the ultrasound signal at the lung surface. In contrast, when air is examination time (<5 min) and high intra- and interobserver repro-
replaced by tissue of similar acoustic impedance to soft tissue, such ducibility.12,13 With increased availability of portable and pocket-
as in cases of pneumonia, ultrasound is transmitted, allowing sized POCUS devices, understanding of LUS can be additive to
distinct image formation.4 clinical data in the evaluation and management of acute decompen-
Lung ultrasound (LUS) was pioneered by Dr. Daniel Lichtenstein sated heart failure (ADHF) or shock.3,14 As providers are frequently
in 1989 at the University Hospital Ambroise Par
e.5 This modality called to perform emergent bedside echocardiography, a basic under-
has gained significant acceptance across fields such as critical care standing of extracardiac findings would be additive in answering the
and emergency medicine, as it allows rapid bedside assessment of pa- clinical question and further elucidating the patient’s noninvasive he-
tients with respiratory failure without the drawbacks of conventional modynamic profile. In the face of the coronavirus disease 2019
radiography and chest computed tomography (CT).6,7 Furthermore, (COVID-19) pandemic, with cardiologists often deployed to
LUS is additive to echocardiography and is part of multiple point-of- COVID-19 units to assess patients with complex cardiac and pulmo-
care ultrasound (POCUS) protocols in the evaluation of hypotension, nary derangements, this skill is particularly important.
shock, and cardiac arrest.3,5,6 This ultrasound imaging modality has Although LUS may be considered a novel application of ultra-
been proved to be superior to portable chest radiography, is more sound in cardiology practice outside of acute care, echocardiogra-
rapid and less resource intensive than chest CT, and is considered phy societal awareness and application of this imaging modality
has traction. The National Board of Echocardiography
From the Division of Cardiology, Department of Medicine, New York University Examination of Special Competence in Critical Care
School of Medicine, New York, New York (E.Y., J.M.H., M.S.); the Department Echocardiography content outline includes lung and pleural ultra-
of Emergency Medicine, Hospital of the University of Pennsylvania, Philadelphia, sound as topics under the section of ‘‘integrated ultrasound imag-
Pennsylvania (N.L.P.); and the Division of Pulmonary, Critical Care, and Sleep ing.’’15 In this article, we review LUS techniques, applications,
Medicine, Department of Medicine, New York University School of Medicine, and findings associated with different pathologies as they would
New York, New York (H.S.).
be relevant to cardiologists. In the hands of trained providers,
Neil J. Weissman, MD, FASE, served as guest editor for this report. this safe, portable, and repeatable diagnostic imaging modality
Conflicts of Interest: Dr Horowitz consults for Inari Medical, Penumbra and AMBU. can reduce patient cumulative radiation exposure, prevent unnec-
All other authors report no competing interests. essary tests, and enhance clinical care at the bedside.
Reprint requests: Eugene Yuriditsky, MD, Division of Cardiology, Department of
Medicine, New York University School of Medicine, 530 First Avenue, Skirball
9R, New York, NY 10016 (E-mail: eugene.yuriditsky@nyumc.org). IMAGING PRINCIPLES
0894-7317/$36.00
Copyright 2021 by the American Society of Echocardiography. The principles of LUS are founded in direct visualization of anatomic
https://doi.org/10.1016/j.echo.2021.08.009 structures and uniquely to the interpretation of artifacts that would
1
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- 2021

Abbreviations
normally limit imaging.2,4,10 In Scanning Technique
normal aerated lungs, the pleura Traditionally, the transducer is placed perpendicular to the ribs with
ADHF = Acute is the only visible structure, as air the indicator facing cephalad. Alternatively, it can be positioned par-
decompensated heart failure beneath the pleura dissipates the allel to the intercostal space to visualize a larger segment of the
BLUE = Bedside lung ultrasound beam. In contrast, pleura.11 LUS can be performed with the patient in any position.
ultrasound in emergency pleural and parenchymal disease There are multiple imaging protocols described in the literature,
alters tissue characteristics and each tailored to a specific clinical scenario ranging from simple four-
COPD = Chronic obstructive
generates signature artifacts. region scans to >28-region scans.3,5,6,20,21 There are two scanning
pulmonary disease
Although LUS is commonly protocols we believe are most relevant to cardiologists in the rapid
COVID-19 = Coronavirus used to evaluate for paren- evaluation of respiratory failure at the bedside: the bedside lung ultra-
disease 2019 chymal pathology, it may also sound in emergency (BLUE) protocol and scanning at the third inter-
CT = Computed tomography be used to assess for disease of costal space.
the parietal pleura and
FALLS = Fluid administration abnormal fluid collections
limited by lung sonography The BLUE Protocol
around the lung.
HF = Heart failure The BLUE protocol is designed for rapid diagnosis of respiratory fail-
ure in a supine patient, with scanning limited to three zones per hemi-
LUS = Lung ultrasound Equipment and Settings
thorax (Figure 1).5,16,22,23 Zones are defined as follows:
Portable POCUS machines,
PE = Pulmonary embolism
The upper BLUE point is located at the anterior chest at the midclavicular
including handheld devices, are
PLAPS = Posterolateral suitable for the performance of line and second to third intercostal space.
alveolar and/or pleural LUS. The technology is simple,
The lower BLUE point is located at the lateral chest at the anterior axillary
syndrome line and just above the nipple.
as there is no requirement for fil-

The posterolateral alveolar and/or pleural syndrome (PLAPS) point is
POCUS = Point-of-care ters, harmonic imaging, or located at the posterior axillary line at the most inferior point above the dia-
ultrasound Doppler.5,11,16 The probe, pre- phragm. The PLAPS point allows the diagnosis of consolidation and pleural
set, and scanning technique effusions.
varies on the basis of the clinical question. When performing an ex-
amination to assess for interstitial lung water (B-lines), images are
optimized by selecting the phased-array or curvilinear transducer, Scanning at the Third Intercostal Space
using the lung preset, the focal zone set to the level of the pleura, tis- It has been demonstrated that in a semisupine patient, signs consistent
sue harmonics off, gain increased in the far field, and a scanning with pulmonary edema (‘‘wet spots’’), described subsequently, are
depth of roughly 15 cm on the basis of the habitus of the patient.17 most prominent at the third intercostal space along the midaxillary
When assessing more superficial pleural-based structures, the image and anterior axillary lines.24 As the diagnosis of heart failure (HF),
is optimized by using the high-frequency linear transducer, with gain semiquantitative analysis of pulmonary edema, and differentiation
set so that the rib shadow is black and the pleural line is white, focal from alternative causes of dyspnea are of most interest to cardiolo-
zone at the pleural line, and the depth varying on the basis of the pa- gists, this simple four-point scan may offer an optimal balance be-
tient’s habitus. tween accuracy and simplicity.

Imaging Transducers SIGNS AND FINDINGS ON LUS

Although standard echocardiography is performed using a phased-
There are a number of common signs described on LUS to aid in the
array transducer, LUS can be performed with a variety of transducers.
differentiation of various pathologies (Table 1).5,11,14,18 Much of the
Linear, phased-array, or curvilinear transducers can be used in LUS
nomenclature assigned to these findings originates from Dr.
with specific advantages and disadvantages to each selection accord-
Lichtenstein’s original description of pulmonary findings with ultra-
ing to the clinical question6,18,19:
sound and have persisted as the field of work has expanded. A limi-

High-frequency linear probes in the range of 7 to 13 MHz provide the best tation of LUS is that the pathology must extend to the pleura to be
imaging of the pleura and are most suited to evaluate for lung sliding to amenable to sonographic evaluation, as intraparenchymal and medi-
assess for pneumothorax or parietal pleural-based pathology. In larger pa- astinal pathology may not be well visualized. Establishing the diag-
tients, beam penetration may be insufficient, as depth is usually limited to nosis of pulmonary edema and differentiation from alternative
6 cm. causes of dyspnea and/or pain are of most interest to cardiologists.

Curvilinear probes in the range of 1 to 5 MHz have improved penetration
LUS findings must be integrated with clinical data and pretest
for deeper structures such as pleural effusions or consolidated lung. Initial
probability.
screening for deep and superficial structures can be performed with this
transducer. The large footprint of the transducer can make scanning be-
tween ribs more challenging, though it allows information to be obtained The Normal Pattern
from across multiple rib spaces at once.
With the ultrasound transducer placed perpendicular to a rib space,

Phased-array probes in the range of 2 to 5 MHz offer a smaller foot-
the hyperechoic pleural line, also termed the visceral-parietal pleural
print compared with curvilinear probes, are most accessible to the cardi-
ologist, and allow both LUS and cardiac ultrasound. These transducers interface, is visualized deep to the ribs (Figure 2A). The ‘‘bat sign’’ de-
are great multipurpose devices for pleural, parenchymal, and cardiac scribes the view obtained with the ribs appearing as wings. Lung
imaging. sliding represents the normal horizontal side-to-side motion of the
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Features almost constant of B-lines are as follows:

HIGHLIGHTS

they arise from the pleural line,

they move in concert with lung sliding,

LUS has gained wide acceptance, is simple, and is additive to
they are well defined and laserlike,
echocardiography.
they are long and spread vertically to the edge of the screen ($13 cm in

LUS can rapidly assist in the evaluation of acute dyspnea. depth),

B-lines, a finding in pulmonary edema, are diagnostic and prog-
they often obliterate A-lines, and

they are hyperechoic.
nostic in HF.
Vertical artifacts other than B-lines can be identified on LUS but do
not meet the above criteria. For instance, Z-lines are short, do not
visceral pleura over the parietal pleura during spontaneous and me-
abolish A-lines, and have no pathologic significance, while E-lines
chanical respiration.5,19,25 Flickering or shimmering visualized at the
arise above the pleural line in subcutaneous emphysema.3,5 As B-lines
pleural line during respiration occurs when the visceral and parietal
are commonly reflective of interstitial or pulmonary edema, this
pleural are normally opposed (Video 1).3,25
finding is of most interest to cardiologists. In a large meta-analysis of
M-mode helps define lung movement relative to the motion of su-
1,301 patients, the sensitivity and specificity of B-lines for pulmonary
perficial structures.5,6,11 The M-mode corollary to lung sliding is
edema were 97% and 98%, respectively (Table 2).29,30 Distinguishing
termed the ‘‘seashore sign.’’ The stationary chest wall and subcutane-
the various alveolar or interstitial processes requires additional clinical
ous tissue appear as parallel lines above the pleura, analogous to water
and sonographic information, as subsequently described. In pulmo-
on the shore. Lung motion with respiration (motion of the alveolar
nary congestion, B-lines are dynamic; just like pulmonary edema,
septae below the pleural line) creates a speckled or grainy appearance
they can resolve rapidly with treatment.4,31-34 By guidelines, three
analogous to sand appearing below the pleura (Figure 2B).
or more B-lines should be noted in at least two zones
A-lines are reverberation artifacts appearing as repetitive, horizon-
bilaterally.6,23,35 As gravity alone can lead to posterior interstitial
tal, equidistant reflections of the hyperechoic pleural line and are
changes, only anterior B-lines are considered in the BLUE protocol.
indicative of gas beneath the pleura. As the ultrasound beam encoun-
ters the boundary between visceral pleura and air beneath, >99% of
the beam is reflected back, with the pleural line appearing as a white Pneumothorax
band (Figure 3, Video 2).5,8,26 The ‘‘A-profile,’’ defined by the pres- Pneumothorax results in air in the potential space between the
ence of lung sliding together with A-line artifacts, is consistent with visceral and parietal pleura and abolishes ultrasonographic lung
a normal pattern.5,6,26 However, such a pattern may also be present sliding (Video 5).5,6,11,18 In a positive pneumothorax scan, the
in the setting of disease processes sparing the parenchyma (i.e., pleural line appears as a static structure without shimmering over
asthma, pulmonary embolism [PE]). the respiratory cycle. If B-mode imaging is equivocal, M-mode scan-
ning serves as a confirmatory tool. The M-mode corollary to absent
Alveolar and Interstitial Pathology Including Pulmonary lung sliding is termed the ‘‘barcode sign’’ or the ‘‘stratosphere sign.’’
Edema In contrast to the sandy appearance below the pleural line with
normal lung sliding, repetitive horizontal lines are visualized both
Reverberation artifacts generated from impedance mismatch be-
above and below the pleural line (Figure 2C).5,6,25 B-line artifacts
tween air and fluid-filled or thickened intralobular septae are termed
are absent in pneumothorax, as these arise from the visceral pleura
B-lines.5,11,23,26-28 The presence of three or more B-lines at a single
and cannot be visualized when there is air inhibiting contact with
intercostal space, termed the ‘‘B-profile,’’ is indicative of an
the parietal pleura.
alveolar or interstitial process such as pulmonary edema, acute
The absence of lung sliding suggests the presence of a pneumo-
respiratory distress syndrome, or pulmonary fibrosis
thorax. However, a ‘‘lung point,’’ which is the transition zone exhibited
(Figure 4, Videos 3 and 4).23,26,28

Figure 1 Chest landmarks. (A) The upper and lower BLUE points identified on the anterior chest. (B) PLAPS point as the intersection
between the lower BLUE point and the posterior axillary line.
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Table 1 Signs and definitions on LUS

Sign Sonographic description Clinical significance

Bat sign Pleural line visualized between two ribs Normal architecture visualized with the transducer placed
at an intercostal space perpendicular to the ribs
Lung sliding Flickering or shimmering at the pleural line with respiration Normal opposition of the visceral and parietal pleural with
motion during respiration
Seashore sign M-mode corollary to lung sliding; motionless chest wall Ancillary sign in the confirmation of lung sliding
creates horizontal ‘‘waves,’’ while sliding creates
‘‘sandy’’ echotexture beneath the pleura
Abolished Lack of opposition between the pleural surfaces or Pneumothorax, pleural adhesions, massive atelectasis,
lung sliding adherence of the visceral and parietal pleural layers pulmonary fibrosis
Stratosphere/ M-mode corollary to abolished lung sliding; parallel Ancillary sign to 2D ultrasound in the confirmation of
barcode sign horizontal lines visualized above and below the pleura abolished lung sliding
Lung point Intermittent lung sliding in contact with the chest wall Specific for the diagnosis pneumothorax and size
during inspiration estimation
A-lines Horizontal reverberation artifacts of the pleural line Gas beneath the parietal pleura indicates absence of
alveolar/interstitial disease; seen in normal lungs,
pneumothorax, asthma or COPD
A-profile A-lines in conjunction with lung sliding Normal parenchymal appearance with respiration
B-lines Vertical, hyperechoic, laserlike reverberation artifacts Alveolar/interstitial process such as pulmonary edema,
extending $13 cm ARDS, pulmonary fibrosis, pneumonia
B-profile B-lines in conjunction with lung sliding Alveolar/interstitial process such as pulmonary edema
without adherent pleural layers
Tissuelike sign Lung has the appearance of liver Translobar consolidation
Shred/fractal sign Irregular, fractal-like appearance at the border of Nontranslobar consolidation
consolidated and aerated lung
Quad sign Fluid demarcated by rib shadows, visceral pleura, and Pleural effusion
parietal pleura
Z-lines Static vertical artifacts, do not move with lung sliding, fade No pathologic significance
with depth
2D, Two-dimensional; ARDS, acute respiratory distress syndrome.

Figure 2 Pleural lines. (A) Normal hyperechoic pleural line visualized between two ribs with the transducer in a perpendicular orien-
tation. (B) M-mode of lung sliding with horizontal lines above the pleura representing the chest wall and grainy echotexture below the
pleural line indicative of lung sliding. This signature is termed ‘‘seashore sign.’’ (C) M-mode of abolished lung sliding appearing as
multiple horizontal lines termed the ‘‘barcode’’ or ‘‘stratosphere’’ sign.
Journal of the American Society of Echocardiography Yuriditsky et al 5
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Figure 3 A-lines. (A) Two-dimensional image of A-lines, reverberation artifact from the pleural line, obtained with a phased-array
transducer. (B) Chest CT of normal lung parenchyma for reference.

Figure 4 B-lines. (A) Two-dimensional image of multiple B-lines in a patient with pulmonary edema obtained with a phased-array
transducer. (B) Pulmonary edema on chest CT.

Table 2 Selected meta-analyses evaluating sensitivity and specificity of LUS in various clinical scenarios

Diagnosis Ultrasound findings Number of patients Sensitivity (%) Specificity (%) Reference

Pulmonary edema B-lines 1,075 94 92 27

B-lines 1,301 97 98 26
Pneumothorax Abolished lung sliding, absent B-lines 1,048 90 98 34
Abolished lung sliding, absent B-lines, lung point 7,569 88 99 33
(hemithoraces)
Pneumonia Focal B-lines, consolidation with air bronchograms 742 95 90 36
Focal B-lines, subpleural consolidation 5,108 92 93 37
PE Wedge-shaped subpleural lesions 1,356 85 83 39
Wedge-shaped subpleural lesions 887 87 82 40
Pleural effusion Anechoic or hypoechoic space 1,554 94 98 35
COPD/asthma A-profile without PLAPS 527 78 94 42
exacerbation

by lung sliding of the noncollapsed lung that contacts the visceral more sensitive (52% vs 88%, respectively).36,37 Although the pres-
pleura and the collapsed lung that does not connect, is most specific ence of a lung point rules in pneumothorax, this finding may be ab-
sign for this pathology (Video 6). Although chest radiography and sent in cases of a small or posterior pneumothorax. Similarly, lung
LUS are both very specific for pneumothorax, LUS is significantly sliding may be absent in the setting of prior pleurodesis, pneumonia,
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Figure 5 Pleural effusion. (A) Two-dimensional image obtained with a phased-array transducer demonstrating an anechoic pleural
effusion with atelectatic lung. The liver is visualized to the right of the image, and the spine is apparent beneath the effusion. (B) Chest
CT demonstrating a pleural effusion for reference.

Figure 6 Lung consolidation. (A) Two-dimensional image of consolidated lung obtained with a phased-array transducer. The consol-
idated lung appears similar in echotexture to the liver (right) and is contained within a pleural effusion. (B) Additional example of pneu-
monia with air bronchograms visible within the consolidation.

pulmonary blebs, and contusion and therefore cannot be taken the presence of a mirror artifact above the diaphragm suggests a
outside of the context of the patient. lack of pleural effusion. Several studies have evaluated echogenic find-
ings of pleural fluid to determine if effusions are exudative or transu-
Pleural Effusion dative.39,40 For instance, presence of complex fluid with septations is
consistent with an exudative effusion.
In cardiology, we are accustomed to visualizing pleural effusions in
standard echocardiographic windows. Placing the transducer at the
PLAPS point on either side, just slightly above the diaphragm at the Consolidation and Atelectasis
posterior axillary line, provides an alternative window.5,6 The indica- Lung consolidations are commonly located at the PLAPS point. The
tor is directed cephalad with the diaphragm and liver or spleen located distinction between atelectasis and consolidation is often challenging.
at the right side of the image. Effusions appear anechoic or hypoechoic A large, translobar consolidation has the echotexture of liver termed
in contrast to consolidated lung, which appears as a tissue density the ‘‘tissuelike’’ or ‘‘hepatization’’ sign.6,19,41,42 Other findings may
commonly referred to as ‘‘hepatization’’ (Figure 5, Video 7).6,19,38 include an irregular, fractal-like line between consolidated and
This view eliminates the need to distinguish pleural effusions from aerated lung, termed the ‘‘shred sign.’’ Air bronchograms, white
pericardial effusions, which, with poor echocardiographic windows, tubular structures within a consolidation, may be observed in cases
may be challenging. Air-filled lungs obscure visualization of the spine of pneumonia (Figure 6, Video 8).5,6,43 With findings of focal B-lines
above the diaphragm. In the setting of pleural effusion, ultrasound and air bronchograms, LUS has been shown to be up to 95% sensitive
waves are transmitted through the fluid, allowing visualization of the and 93% specific for the diagnosis of pneumonia in large meta-
spine as an additional clue to the presence of an effusion. Similarly, analyses (Table 2).41,42
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Figure 7 COVID-19 LUS findings. (A) Two-dimensional image of an irregular, fragmented pleural line obtained using a high-frequency
transducer. (B) Subpleural consolidation visualized as a hypoechoic structure with irregular margins.

Pulmonary Embolism nonhomogenous and patchy in contrast to cardiogenic pulmonary

The sensitivity and specificity of LUS for PE are upward of 83% and edema. The pleural line may appear irregular with areas of disconti-
85%, respectively, with the predominant finding being pleural-based nuity (Figure 7A). Subpleural consolidations appear as hypoechoic
consolidations consistent with infarction.44,45 Alternatively, the structures with irregular (shredded) borders (Figure 7B, Video 9).
finding of A-lines with lung sliding in the setting of acute dyspnea Handheld POCUS devices with wireless tablets can be placed in sepa-
or respiratory failure, in conjunction with deep venous thrombosis, rate plastic covers to minimize contamination risk. Additionally, the
is highly specific for PE.5,26 Multiorgan sonography, including the teleguidance feature on some handheld devices can limit the need
combination of LUS, lower extremity venous sonography, and echo- for imaging experts to have direct patient contact.50,51 In this disease,
cardiography, in the assessment of the right ventricle has been LUS findings may be predictive of clinical outcomes such as intensive
described as a reasonably sensitive and specific approach for the diag- care unit admission and mortality.52,53 A scoring system incorporating
nosis of PE.46 the extent of B-lines and the presence of consolidation, in conjunction
LUS with echocardiography cannot be used alone for the diagnosis with limited echocardiographic findings evaluating ventricular func-
of acute PE, because sonographic findings are most commonly asso- tion, may be valuable in identifying those at risk for certain clinical
ciated with intermediate- and high-risk PE, and therefore low-risk clots end points.53
may be missed. However, it can function as an adjunct or valuable
alternative in the emergency setting or when CT is not immediately
available or the patient is too unstable to move or to evaluate for right CLINICAL APPLICATIONS OF LUS
heart strain when assessing the significance of the injury. Similarly, in a
patient with hemodynamic instability and no findings of PE on ultra- The main LUS protocols are targeted toward emergency and critical
sound, the root cause of instability is unlikely secondary to acute PE. care providers and tailored to provide a prompt diagnosis of respira-
tory failure and circulatory shock integrating cardiac ultrasound in a
holistic approach.5,6,20,54 For cardiologists, LUS can be a key diag-
Chronic Obstructive Pulmonary Disease and Asthma nostic tool to be incorporated into the care of patients in the cardiac
Chronic obstructive pulmonary disease (COPD) and asthma are intensive care unit. Additionally, this modality has gained traction in
bronchial diseases sparing the pleural surface and parenchyma. The the assessment of pulmonary congestion before hospital discharge
finding of bilateral lung sliding with A-lines without PLAPS is the and in the outpatient setting.24,32,55-58
sonographic finding consistent with COPD or asthma and is 94% spe-
cific for this condition.26,47 Although this pattern makes pleural and
LUS in Decompensated HF in the Nonemergent Setting
parenchymal processes unlikely, it can also be a normal finding or
observed in the setting of PE. ADHF is a diagnostic challenge. Physical examination, chest radiog-
raphy, and natriuretic peptides have limited accuracy in the detection
of pulmonary congestion.6,26,29,30,34,35 LUS is recommended by the
COVID-19 European Society of Cardiology guidelines in the diagnosis and man-
LUS is of particular interest during the COVID-19 pandemic. Early in agement of decompensated HF.57 Adding LUS to a standard diag-
the US pandemic, diagnostic testing was limited, personal protective nostic approach of dyspnea and suspected HF in the emergency
equipment shortages inhibited traditional diagnostic practice, and department, 19% of patients are reclassified in terms of diagnosis.35
although chest CT was specific for the disease, this imaging modality The quantity of B-lines has significant correlation with left-sided filling
was generally limited to stable patients. Sonographic findings of pressures, radiographic pulmonary edema, and measures of extravas-
COVID-19 pneumonia are those typical of acute respiratory distress cular lung water.24,33,56,59 Compared with echocardiographic assess-
syndrome.48,49 B-lines are frequently seen but may be ment of left atrial pressure, LUS is exceedingly simple.59 When
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Figure 8 Pulmonary edema. (A) Pulsed-wave Doppler at the mitral valve demonstrating rapid E-wave deceleration. (B) Tissue
Doppler at the medial mitral annulus demonstrating low e0 velocities consistent with elevated left atrial pressure. (C) Multiple B-lines
obtained using a phased-array transducer. (D) Pleural effusion on LUS.

encountering a patient with suspected ADHF, the major questions to can identify consolidation or pleural effusion. Following is a simplified
ask are whether there are multiple diffuse B-lines consistent with pul- LUS approach to the patient with acute respiratory failure.
monary edema and whether an alternative etiology explains the clin-

Lung sliding with extensive B-lines (B-profile) defines alveolar-interstitial
ical presentation (i.e., pneumonia, COPD).
syndrome and is very sensitive and specific for pulmonary edema, a more
There is mounting evidence that LUS can be used in the outpatient
common entity than interstitial lung disease. Subsequent workup with car-
setting to titrate medications, reduce hospitalizations, and improve diac ultrasound can define the mechanism of pulmonary edema (i.e., left
patient-reported quality metrics.7,56 B-lines detected by LUS in the ventricular systolic dysfunction, acute valvular regurgitation).
outpatient setting among patients with HF are associated with read-
Lung sliding with A-lines (A-profile) excludes pulmonary edema as a cause
mission and mortality even in the absence of auscultatory findings of acute respiratory failure and makes the diagnosis of COPD, asthma, or PE
to suggest pulmonary edema.57,60 Additionally, the number of B-lines more likely. Venous sonography can be added to the workup; deep venous
present on hospital discharge has been associated with mortality and thrombosis with an A-profile in a patient with acute dyspnea is highly spe-
hospitalization.61 When compared with standard follow-up outpa- cific for PE. Additional evaluation of the PLAPS point can further define
tient care, a LUS-guided diuretic management approach has been pneumonia or pleural effusion when the diagnosis is in question.

Abolished lung sliding with A-lines (A0 -profile) raises concern over pneumo-
shown to decrease the number of decompensations and improve
thorax, as this pattern suggests that the visceral and parietal pleura are unop-
walking capacity.62 LUS has been implemented during exercise stress
posed. Identifying a lung point, the transition between present and
testing; fewer B-lines are associated with event-free survival.20 As abolished lung sliding, is highly specific for pneumothorax.
these artifacts are dynamic and resolve with diuresis and dialysis,
Abolished lung sliding with B-lines (B0 -profile) is most consistent with pneu-
frequent LUS can be an adjunct to monitoring progress and in the monia at a particular zone. Unlike the A0 -profile, abolished lung sliding in this
diagnosis of euvolemia in this population. scenario is consistent with adhesion of the two pleural surfaces. Identifica-
tion of lung hepatization or air bronchograms defines a pneumonia.
LUS in Acute Dyspnea As the diagnosis of ADHF is most relevant to cardiologists when
When evaluating acute respiratory failure with LUS, the first questions confronting patient with dyspnea, particularly in those who carry
to ask are (1) Is lung sliding present? and (2) Do I see an A-lines or B- the dual diagnosis of COPD and HF, simply evaluating for the
lines?5,18,19,26 This assessment can be performed using the upper and B-profile would greatly narrow further investigation. Figure 8
lower BLUE points, while interrogation of the PLAPS point thereafter depicts an example of a patient with acute respiratory failure;
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Figure 9 Examples of pathologies detected using the FALLS protocol in shock. (A) Echocardiogram demonstrating pericardial effu-
sion in a patient with clinical tamponade. (B) Echocardiogram demonstrating right ventricular dilation in a patient with PE and shock.
(C) LUS M-mode demonstrating pneumothorax. (D) LUS demonstrating pulmonary edema in a patient with cardiogenic shock.

echocardiographic diastolic parameters are consistent with elevated defining the limit of volume repletion. Figure 9 is an example of echo-
left atrial pressure, while LUS confirms pulmonary edema and a cardiographic and LUS pathology encountered in the FALLS
pleural effusion. protocol.

Evaluation of Hypotension and Circulatory Shock

The fluid administration limited by lung sonography (FALLS) protocol CONCLUSION
is an integrated echocardiographic and LUS assessment of circulatory
shock.3,5,6,54 In a stepwise approach, the FALLS protocol is used to LUS is a simple and informative imaging modality that is readily avail-
evaluate for obstructive (i.e., extracardiac causes of pump failure able, takes <5 min to perform, is repeatable, and is safe. It is
such as PE, tension pneumothorax, tamponade), cardiogenic, and commonly used in the evaluation of undifferentiated dyspnea in
distributive shock, with the following questions to improve diagnostic emergency and intensive care medicine, though it is yet to be fully
accuracy in patients with undifferentiated symptoms: adopted by cardiologists. It is sensitive and specific for the diagnosis
of ADHF, greatly outperforming clinical, laboratory, and radiographic
1. Is there a substantial pericardial effusion concerning for tamponade? assessment. Likewise, lack of diffuse B-lines in an patient with acute
2. Is there right ventricular dysfunction suggestive of PE? dyspnea virtually excludes ADHF as a cause and allows the clinician
3. Is there left ventricular dysfunction or severe valvular disease? to explore alternative etiologies. Advances in portable and handheld
4. Is lung sliding absent consistent with tension pneumothorax?
POCUS technology places LUS at arm’s reach of our patients. The
5. Is there a B-profile with left ventricular dysfunction consistent with cardio-
addition of LUS to bedside echocardiography can be invaluable in
genic shock?
6. Is there an A-profile that suggests ‘‘dry lungs’’ and fluid tolerance? making an accurate clinical assessment when faced with respiratory
failure or shock. Cardiology trainees, as well as those managing
Once obstructive and cardiogenic shock are excluded, fluids can acutely ill cardiac patients, should obtain familiarity with this imaging
be administered with ongoing monitoring by LUS, with B-lines modality and use it in routine clinical practice.
10 Yuriditsky et al Journal of the American Society of Echocardiography
- 2021

SUPPLEMENTARY DATA 21. Reisinger N, Lohani S, Hagemeier J, Panebianco N, Baston C. Lung ultra-
sound to diagnose pulmonary congestion among patients on hemodialy-
Supplementary data related to this article can be found at https://doi. sis: comparison of full versus abbreviated scanning protocols. Am J
org/10.1016/j.echo.2021.08.009. Kidney Dis 2021. https://doi.org/10.1053/j.ajkd.2021.04.007.
22. Volpicelli G, Caramello V, Cardinale L, Mussa A, Bar F, Frascisco MF.
Bedside ultrasound of the lung for the monitoring of acute decompen-
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