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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5769_Библиотеки_им_академика_М_И_Перельмана
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20 oracic ultrasound
can coordinate his or her hand with the images on the screen, becoming able to produce not
only orthogonal projections, with recognizable anatomical details, but also variously directed
scans (intercostal oblique, paramedian, coronal, etc.).
Heart ultrasound uses special acoustic windows that will be described in a specific section.
It should be remembered that echocardiography is a real ultrasound and, as such, it should
necessarily avoid thoracic areas where the lung appears behind the wall. e relationship between heart and lung in imaging are often problematic for the physician. Air is a foe for the
cardiologist while it is a friend for the lung sonographer. erefore a coherent sonographic
approach, using lung and heart projections, needs to take into account important border
regions. For example where the lung border covers the heart with the breaths and where an
abnormal respiratory dynamics can allow to diagnose subtle lung and heart pathologies.
➣ Scanning technique
In order to reproduce body regions, the ultrasound probe, properly oriented, is placed, on the
district to explore. Since the ultrasound must pass from the transducer to the skin, and then
into the body tissues without obstacles, it is essential to interpose between the probe and the
skin a medium with low impedance. e most widely used substance is the ultrasound gel.
However other materials or fluids permissive to sound can replace the gel. Skin disinfectants (which however can stain or damage the probe) or plain water can be used. Unlike the
gel, watery liquids increase the friction of the transducer, remain short time on the skin and
therefore require a repeated usage.
➣ Chest scans
e ultrasound examination of the chest is currently conducted with a normal device, not
necessarily advanced by the technological point of view. In this regard there are no data that
allow to determine the best setting for the device, in particular regarding the definition of the
artifacts, both specular (A Lines) or focal (B lines).
In our opinion, the use of specific probes (such as the linear probe), appropriate frequencies
(around 7 MHz) and employing fundamental frequencies, is more representative, in terms
of artifacts, compared to the usual convex probe or to casual settings.
e patient can be studied in the supine or sitting position. is of course depends on his
clinical condition, but also on the thoracic surfaces to be explored and on what the operator wants to highlight. In fact, effusions are studied more easily in a sitting position, while
pneumothorax has its best representation in the supine position.
What determines the accuracy and therefore the timing of a study of the chest is the essence
of what is searched. Since the research object can be a simple marker or a panoramic view, it
is clear that the operating setting of pleuropulmonary ultrasound also influences the scans.
If a patient’s medical history or objectivity is not very specific in terms of pneumology, or
generically of internal medicine, ultrasound plays an important role for a global, or panoramic
thoracic survey. In this context, it can not compete with the capability of overview offered
by conventional chest radiology.
To cover most of the lung surface, it is necessary to perform complete ultrasound scans,
which are generally obtained in two phases. e first one is a general exploration performed
through multiple longitudinal projections on each hemithorax, along the usual anatomical
lines (parasternal, mid-clavicular, axillary, paraspinal) (Figs. 17, 18).
Basic principles 21
Figure 17 – The scans on the chest should avoid bones planes, they should be performed in intercostal
planes or over them (longitudinal scans, in the box).
Figure 18 – The posterior-lateral longitudinal scans on the costophrenic angles are useful to define the
presence of effusions and to study the dynamics of the diaphragm and lung borders (curtain ultrasound
image, in the box).
e second one is performed whenever an anomaly is suspected. is “hot zone” will be
analyzed through local scans, according to various planes and using the most appropriate
frequencies, even through the use of linear probes. ese are capable of amplifying properly
the pleural surface. In this sense, we believe that the linear probe represents a valuable tool
22 oracic ultrasound
to detect the irregularity of the pleural line, the details of its sliding, and its finer vertical
artifactual component.
During the examination, when possible, the patient should be sitting and be able to breathe
on request. e sitting position also allows to explore the posterior regions of the lower lobes
of the lungs and the intercostal windows between the shoulder blades and spine. Finally, the
scans of the supraclavicular fossa, display the pleura of the lung apices.
Frequently the patient’s sitting posture can not be maintained and the examination is reduced
to the execution of anterior, lateral and posterolateral scans, where the patient is slightly lifted
on one side and supine or semi-sitting.
During the investigation different areas of the pleuroparenchymal surface are hidden by anatomical structures or otherwise are difficult to study. ese are the posterior regions covered
by the shoulder blades, peri-clavicular and apical regions, the upper part of the axilla, and
the precordial region occupied by the heart. To overcome this, the probe can be appropriately
tilted, exploring the borders of these regions. Moreover the operator can move up the probe
to the apex of the axilla and on the supraclavicular fossa. However, even with due precaution,
some parts of the pleuroparenchymal surface may be hidden to ultrasound (about 20% of
the thoracic lung fields).
Peculiar clinical conditions, or environmental setting (e.g. patient with dyspnea, trauma, in
ER during a primary clinical evaluation) can take advantage of a simplified methodology
(focused exploration), opposed to a systematic exploration of the chest. Many of these issues
will be clarified in different chapters, but, as a general guideline, we can identify two basic
focused methods.
e symptom-guided exploration uses targeted scans in symptomatic areas. e pleuritic pain,
in fact, tends to orient the scans on the dependent regions of the chest to highlight effusions.
Oriented scans can be used in the case of epicritic pain directly above the symptomatic region,
to produce any images of pleural irregularities, white lung or consolidations. e same logic
can drive scans on contused regions or where a rib fracture is suspected. Even an auscultatory
or focal percussive finding can direct the probe into thoracic regions, often rich in findings.
is methodology represents a modern blend of classic symptomatology and semiotics, and
clinical technology.
Finally, we consider a focused ultrasound evaluation aimed at “hot zones”. Hot zones are
thoracic parietal regions whose ultrasound exploration is statistically more likely to produce
artifacts with diagnostic significance. e purely physical concept according to which air settles in non-dependent cavity regions, while water lies in a dependent position, indicates the
opportune scans. It allows, in supine patients, to direct the exploration of a pneumothorax
primitively into the lower parasternal regions (deep sulcus area) and to search pleural effusions
over the dependent posterobasal areas of the chest. Obviously, in the sitting patient the best
definition of free pleural effusions is obtained exploring the supradiaphragmatic posterior and
lateral regions. For reasons not yet fully studied, B Lines of left heart failure become evident
in the subclavian lung and axillary regions.
Basic principles 23
➣ Display of images on the screen of the ultrasound machine
In abdominal ultrasound, there is a convention for the orientation of images that are played
on the screen.
In transverse scans images are displayed in such a way that the left side of the screen shows
the patient’s right side and the right side of the screen the left side of the patient. e result
is a transverse or axial tomographic image similar to that one of CT.
In sagittal or longitudinal scans, the left side of the screen corresponds to the patient’s head
and the right side of the screen to the patient’s feet.
Of course, in each image the scanned surface appears at the top and the deep one at the
bottom of the screen.
It is curious, but certainly not surprising, that there isn’t a proposal for encoding the images
that are produced with the ultrasound study of a chest yet. However there is no need to deviate
from the methodology used for years in the abdominal area, which we refer to.
Chest scans vertically follow the anatomical lines (parasternal, midclavicular, axillary, paravertebral) and horizontally the intercostal spaces, thereby generating longitudinal, coronal and
not fully axial sections. Carefully following the intercostal spaces with the linear probe the
ribs and their related spaces run from top to bottom and from back to front. It is therefore
essential to capture images with a clear orientation, allowing to standardize, on the image
obtained, a cranial, caudal, medial, lateral, front and rear side.
Similarly to the general principles of clinical ultrasound, in the longitudinal projections the
cranial part of the image is reproduced to the left on the screen and the caudal one (diaphragmatic in the case of the chest) to the right.
In the transverse (axial) projections anatomy located to the right side of the patient is displayed
in the part of the screen to the left of the operator; the part on the left side of the patient is
displayed in the part of the screen to the right of the operator.
e anterior parts are displayed in the upper part of the screen and the posterior parts in the
lower parts of the screen (Figs. 19, 20). Except for special cases, this textbook follows the
above-mentioned rules.
H
E
A
D
LONGITUDINAL
SCAN
Figure 19 – Longitudinal scan: the cranial portion of the image is on the left of the screen, the caudal
one is on its right; the anterior parts are displayed in the upper part of the screen, the posterior ones are
in the lower part of the screen.
Left
Right
24 oracic ultrasound
Transverse
scan
Figure 20 – Transverse scan: the right side of the patient is displayed on the left of the screen, the left
side of the patient is displayed on the right of the screen.
PATIENT'S RIGHT SIDE
Left
Right
➣ The orientation of the probe for the purpose of creating the
correct image
So that the images on the screen appear correctly oriented, the probe placed in contact with
the skin needs a proper orientation. ere are at least three methods to control this orientation. e probe should be held as a pen to finely adjust the scanning movements. A first
method involves the placement of a single angle of the probe on the skin of a patient. In
case of transverse scan, the right side of the probe (in contact with the middle finger of the
operator) explores the left side of the patient in the supine position, and it corresponds to the
right side on the monitor (for the viewer). In case of longitudinal scan, the right side (for the
viewer) of the probe explores, through a clockwise rotation, the caudal part of the patient.
A second method uses landmarks normally placed on the probe, which can be protrusions
or bright points. In this case, the operator makes sure that the landmark of the probe is on
the same side of a mark that appears on the monitor.
Finally, the third method consists in sliding the probe on the patient’s skin. In a transverse
scan the probe is correctly oriented when sliding to the left results in a shift of the images
on the screen to the right and vice versa. Despite the banality of these concepts, practice is
required in order to gain the experience needed to rapidly automate these maneuvers. Initial
exercises are usually carried out on “volunteers”.
➣ Ultrasound practice on the chest
Anatomical and technical knowledge is not enough to put into practice the procedures on
the patient, whether they are evaluative or operational. In the diagnostic activity an acceptable level of competence requires the execution of tens or even hundreds of tests, initially
supervised by an expert, then executed independently. e same applies to operative ultrasound and is of course valid in the specific field of thoracic ultrasound, whose elementary
semiotics
12,14
may appear relatively simple. We believe that the simplicity of the normal and
Basic principles 25
pathological semeiotics in thoracic ultrasound is a thing of the past, where the signs appeared
in fundamental terms of A and B Lines
9,15
. An initial systematization through the analysis of
the concentration of B Lines16 and the identification of white lung17 has highlighted many
problems and poor knowledge. e description and the correct interpretation of the acoustic
roughness of the visceral pleura along with the study of the so called “alveolar syndrome”, have
expanded the variety of meaningful images that can be obtained. However the correlation
between ultrasound lung images and different lung diseases requires an expansion.
Actually, a distinction is increasingly clear between “real ultrasound” for non-aerated tissues
(chest wall, ribs, pleura, effusions, thickening, atelectasis), and “artifacts ultrasound” of the
aerated lung parenchima. is is not a real ultrasound18.
If we simply consider “artifacts” as complex signals derived from the acoustic interaction
on an equally complex anatomo-pathological substrate and detected by the machine, the
distinction is incertain.
However “real” echography is anatomy represented in a picture, while “artifact” ultrasound
is an undefined and not clearly studied entity. It is useful to produce fundamental diagnosis
(wet or dry lung in the first place), but certainly it does not produce anatomical pictures.
is makes clear that a long path of knowledge is still needed. Probably one of the first useful knowledge to be acquired, will be the boundary between real ultrasound and “artifacts
ultrasound” in the lung, in terms of density or aeration of the tissues. ese concepts will be
exposed in a specific chapter.
As it will appear throughout the text, the current state of knowledge about thoracic ultrasound leverages common ultrasound technologies. ey usually return images that are true
or fictitious, in accordance with the normal interaction processes of acoustic energy with the
organic tissues, and in this specific case, with aerated parenchyma.
is means that the equipment to be used and the knowledge to be acquired in the field of
physics do not differ from what is already the cultural heritage of an ultrasound operator.
e principles that provide visualization and quantification of the flows according to Doppler,
color or power principle, particularly useful in cardiology, are the same that are applied in
every area of the body.
Despite these overlaps, it is useful to define some peculiarities which, although subject to
changes linked to the future development of the method, currently characterize the lung
ultrasound, in particular the emergency one.
• e images that are acquired in chest ultrasound allow analysis of shapes (morphology),
analysis of artifacts and dynamic (functional) valuations.
• e examination of the chest wall is a normal ultrasound of the superficial tissues.
• Except for the cardiac window, the examination of normal lung fields is inevitably reduced
to the morphological study of the pleura and its dynamics.
• e pleural line is in the normal subject a highly reflective structure preventing the expres-
sion of a deep morphologic ultrasound in terms of echotexture.
• Any process that decreases the acoustic impedance of the pleural plane, such as a lung
consolidation or a tumor arising at the level of the pleura, allows an anatomic assessment.
It eliminates the air barrier and represents an acoustic window.
• e bronchial tree and pulmonary vessels normally cannot be seen. Whenever an acoustic
window is created in the lung, an air or fluid bronchogram is expressed and intraparenchimal vessels show a morphological and Doppler pattern.
26 oracic ultrasound
• Acoustic artifacts of the lung result from the interaction of the ultrasound beam with air
and appear different depending on the air content of the part studied and on the homogeneity of its distribution.
anks to these premises many concepts become clear. e physician interested in lung
ultrasound should know some basic principles before performing an ultrasound study of the
chest. ese are summarized below and will be expanded in the following pages.
• Ultrasound of the chest, as well as the physical examination, is a diagnostic method that
must be integrated with the patient’s clinical data and with any additional instrumental
investigations.
• e main indication to perform a chest ultrasound examination is the emergency setting
and most of the knowledge about chest ultrasound derive from critically ill patients (ICU,
ER). is is supported by the culture, the “transversal” goal directed methodology, typical
of emergency and by the ease of use point of care of ultrasound. Table 2 summarizes these
characteristics of emergency ultrasound opposed to elective ultrasound.
• Being directed at professionals from different backgrounds, in its basic applications chest
ultrasound should avoid the use of high technologies and advanced machines. In this textbook only the essential information are provided for color and power Doppler methods,
the general importance of which is recognized within specialist fields.
• is textbook will not provide any information on other technologies typical of modern
ultrasound (Tissutal Harmonic Imaging, Compound) because, although their use is foreseeable in the future, to this day the available data are not sufficient.
• For what concerns ultrasound contrast agents19 used under low mechanical indexes, we
will provide only some notions, useful for the study of lung consolidations and especially
suitable for their differentiation.
• All of the above does not mean that chest ultrasound should be “poor”. e study of
the many artifactual components of the lung is a very specific and complex field and the
“wealth” of the method lies in the ease of implementation and in its extraordinary ability
to inform the clinician in relation to key events in a very short time.
Table 2 – Differences between elective and emergency ultrasound
Elective ultrasound Emergency ultrasound
Carried out in a defined specialized
setting, almost never at the bedside
Carried out by a specialist (radiologist or
clinical specialist)
Generally explores an organ or apparatus No borders of organ or apparatus, goal directed
It results in a diagnosis or is integrated into
a specific not urgent path
It furnishes specific information Aimed at identifying essential diagnostic categories
Carried out whenever it is necessary to assist a
critically ill patient, at the bedside
Carried out by the clinician treating the patient, as
an extension of the clinical evaluation
Always integrated into an emergency diagnostic
clinical context
to be sharpened in semi-emergency or election
Basic principles 27
➣ Meaning of chest ultrasound
Among the patients who come to the observation of emergency and critical care physicians,
many subjects report chest symptoms. ese include pain with variable specificity for pleural,
myocardial or pericardial diseases, dyspnea, cyanosis, cough, fever, shock. e gravity is variable, up to situations that require immediate diagnosis and treatment
Pleuro-pulmonary and cardio-vascular pathology is relevant and represents whole chapters
of clinical practice in which the role of ultrasound examination, except in its more properly
cardiac and angiological aspects, has always been marginal. e main investigation in thoracic
pathology, after the physical examination, has been, and commonly remains, the plain chest
radiograph.
Chest X-ray, obviously of inevitable historical importance, has good results in chest diagnostics, because it exploits the physiological contrast of the pulmonary air and solid tissues and
organs. It outlines the cardio-mediastinal shadow centrally, the wall laterally, and enhances
the pulmonary picture, made of vessels, bronchial tree and interstitium22.
Chest X-ray shows coarse and obvious findings, but the expert radiologist expresses his or
her skill analyzing subtle morphological variation of the parenchyma. Hyperlucencies or
opacities needs to be interpreted and attributed to the interstitium or air spaces rather than
to pleural or under-diaphragm images23. is analysis, together with the evaluation of the
distribution of opacity is essential because it often identifies the pathology and has therefore
therapeutic implications.
However, in emergency the quality of radiological imaging very often deviates from the
standard required, penalizing the diagnostic accuracy24 (Figs. 21, 22, 23).
20,21
.
Figure 21 – Bullous emphysema. Plain radiography shows only diaphany in upper regions of the lung
fields. CT is very accurate in defining the true nature of these findings, even quantitatively.
For example, a localized consolidation can be expression of an interstitial or alveolar inflammation (pneumonia), but it can also represent an atelectatic, contused or embolized part of
the parenchyma.
28 oracic ultrasound
seated
Figure 22 – To the left: x-ray of a patient with pulmonary fibrosis. Linear (septal), reticular and
micronodular thickenings are evident, that do not allow, however, to accurately define the anatomy of
the underlying disease. The CT shows more accurately the topography of the lesions and their location
in relation to the lobules, which would be further enhanced with high definition.
supine
Figure 23 – Subject with diffuse interstitial disease, right pleural effusion and right lower lobe
thickening. The x-ray, although pathological, is not very diagnostic. The CT, without contrast agent, is
much more informative.
Basic principles 29
Often it is difficult to correctly attribute an opaque hemithorax to a parenchymal or pleural
disease. Moreover diffuse interstitial expansion can mean many things, from lung stasis to
the wide variety of diffuse interstitial lung diseases25.
In these cases, if a CT scan is not performed, medical history and physical examination are
crucial. ey define the acuteness of the case, the pulmonary or cardiac (or mixed) precedents,
the evidence of trauma and the existence of inflammatory (infectious or not) symptoms26.
Table 3 summarizes limitations of chest radiography and advantages of CT scan.
Table 3 – Limitations of chest radiography and advantages of CT scan
Chest X-ray: limitations
Small differences between normal and pathological tissue are difficult to define
Minor abnormalities of the parenchyma can not be diagnosed
In chest X-ray overlapping of many anatomical structures occurs, which make an accurate
diagnosis difficult
Chest CT: advantages
A high-definition CT provides detailed information of the lung parenchyma
It defines structures dimensionally relevant to the secondary pulmonary lobule
Being a cross-sectional technique the problem of overlapping structures in the image does not exist
However, sometimes (or often) the anamnesis and the physical examination do not resolve
the doubts, as in cases of dyspnea. In dyspnea uncertainties arise when a congestive component is established on a bronchitic and bronchospastic basis, creating complex auscultatory
cases. Otherwise when an interstitial pathology do not generate appreciable findings through
semiotics27.
In an emergency setting, where historical data are fragmented, where time is essential and
where certain instrumental investigations require the transfer of the patient, the differential
diagnosis of acute pleuropulmonary disease becomes a complex and quite treacherous topic.
Beyond clinical objectivity, electrocardiogram, estimation of arterial blood gases and acid-base
balance, the first examination on a “respiratory” patient is the double x-ray projection (PA
and LL) of the chest. In emergency it is very often just the PA chest projection with little or
no cooperative half-seated patient.
e emergency physician must then put a lot of effort into immediately correlating medical history, clinical, laboratory and radiographic data with a diagnostic hypothesis. is
hypothesis may initially be generic (heart failure, chronic obstructive pulmonary disease,
lower respiratory tract infection, occupational pleural disorder, vascular dyspnea etc.), and
then progressively more specified28.
In these situations of “respiratory” uncertainty ultrasound has always been considered to
have little impact. For a long time the lung was erroneously believed to be inexplorable by
ultrasound because of the reverberations of its air content. For many years diseases such as
pneumonia, pulmonary edema or pneumothorax have been considered as clinical manifestations not be investigated with ultrasound.
Recent experiences with the use of chest and lung ultrasound made clear what may be called the
“paradox of the lung” in which the organ is not easily explorable by ultrasound if normal, but
it shows significant acoustic windows when pathological. e disease “uncovers” the organ13.
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