Page 302 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

206 PART 2: General Management of the Patient

B lines with pleural irregularity are characteristic of primary lung injury The procedure is generally performed with the patient in the supine
such as pneumonia, interstitial lung diseases, and ARDS, whereas gener- position. Small effusions may require further position of the patient to
alized confluent B lines with smooth pleural surface are typical of hydro- obtain a good window for access. The scan should be followed promptly
static pulmonary edema secondary to heart failure. The intensity of by needle insertion without any interval movement of the patient, as
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B lines is temporally associated with a variety of disease processes such patient movement may alter the distribution of fluid within the thorax.
as high-altitude pulmonary edema, acute dialysis, PEEP-induced lung When performing ultrasound-guided thoracentesis, the intensivist seeks
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recruitment, and resolution of pneumonia. 30 unequivocal identification of the diaphragm and the underlying liver or
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Lung ultrasonography may be used to distinguish cardiogenic pul- spleen. The inexperienced ultrasonographer may mistake the curvilinear
monary edema from primary lung injury. As a first step, the finding hepato- or splenorenal recess as the diaphragm and the liver and spleen as
of A lines over the anterior chest indicates that the pulmonary occlu- an echo dense effusion, with the catastrophic result of subdiaphragmatic
sion pressure is less than 18 mm Hg in all cases, and is usually less than device insertion. Definitive identification of the underlying lung that is
12 mm Hg. A lines therefore rule out hydrostatic or cardiogenic pul- well away from the needle trajectory is required to avoid pleural lacera-
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monary edema. The finding of confluent diffuse B lines with a smooth tion. Identification of the inside of the chest wall permits measurement
pleural surface is strong evidence of cardiogenic pulmonary edema. 26 of the required depth of needle penetration, as well as determination that
there is sufficient space between the chest wall and the underlying lung for
Alveolar Consolidation: Alveolar consolidation can be diagnosed with
ultrasonography. Consolidated lung has tissue density. It has similar safe needle insertion. The best site is marked and the insertion area pre-
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pared in standard fashion. The needle/syringe assembly is inserted at the
echo density as liver, and so the term sonographic hepatization is apro-
pos. The border between the aerated lung and tissue density of alveolar indicated site and depth while duplicating the angle defined by the trans-
ducer in determining the safe trajectory for needle insertion. Wire and
consolidation may be irregular and may exhibit comet tail artifacts.
Punctate echogenic foci may be visible within an alveolar consolidation. device placement may be checked during the procedure. Real-time needle
guidance is not required for thoracentesis. Following the pleural proce-
These are sonographic air bronchograms. If the air within the bronchus
moves with the respiratory cycle, the bronchus leading to the area is dure, the examiner should check for procedure-related pneumothorax.
Ultrasonography may be used to guide transthoracic needle inser-
patent. Areas of alveolar consolidation may be multifocal, lobar, or
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segmental in distribution depending on the underlying disease process. tion into lung and mediastinal lesions. Consolidated lung and pleural
effusion provide an ultrasound window that allows visualization of
The finding of alveolar consolidation on ultrasonography does not
imply a specific diagnosis. Pneumonia will result in the finding, but so structures that are ordinarily not visible through aerated lung, as air
blocks transmission of ultrasound, so that a lung abscess or lung mass
will atelectasis due to endobronchial obstruction, ARDS with dependent
consolidation pattern, or pleural effusion. In the latter case, pleural effu- may be visualized within consolidated lung. This allows percutaneous
ultrasound guidance of catheter insertion for drainage of lung abscess.
sion predictably results in compressive atelectasis of the underlying lung
with a resultant alveolar consolidation pattern. Pleural symphysis at the site of device insertion must be observed in
order to avoid pneumothorax during the procedure.
Pleural Effusion: Ultrasonography is well suited to identify fluid, which
is characteristically hypoechoic relative to surrounding tissue. Pleural
effusions are common in the critically ill. Ultrasonography is superior CARDIAC ULTRASONOGRAPHY
to supine chest radiography for their identification. It also permits Hemodynamic failure and shock are common problems in the ICU.
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safe thoracentesis in the patient on ventilatory support. Pleural and Proficiency in echocardiography allows the intensivist to quickly cat-
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lung ultrasonography are closely connected, and performance of tho- egorize the cause of shock, to develop a management strategy that is
racic ultrasonography includes routine assessment for pleural effusion. based upon direct visual assessment of cardiac function, and to follow
In the supine patient, pleural fluid collects posteriorly; therefore, the response to treatment and evolution of disease. The efficiency, safety,
search for fluid focuses on the dependent thorax, excepting the unusual and usefulness of the technique supports the concept that echocardiog-
situation of a locculated collection. raphy is an essential skill for the frontline intensivist. When combined
There are three ultrasonographic features of pleural effusion: (1) a relati- with thoracic ultrasonography, there is no other imaging modality that
vely hypoechoic space, (2) subtended by typical anatomic boundaries gives such immediately useful information.
(diaphragm, lung, and the inside of chest wall, (3) with typical dynamic
findings (such as diaphragmatic movement, lung movement, and move- ■ GENERAL PRINCIPLES
ment of echo dense material within the fluid collection). The size of the
effusion may be assessed qualitatively as mild, moderate, or large. Accurate The intensivist deploys cardiac ultrasonography in a manner that is
estimates of volume require detailed measurements that may not be different than the cardiology approach. The intensivist responds to the
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required for typical clinical management. An anechoic fluid collection is patient in shock with immediate beside echocardiography; the study
most likely a transudate, whereas fluid that has visible echo dense complex- is limited and goal directed, the results are immediately used to guide
ity such as fronding or septations is probably an exudate. Very complex management, and the examination is repeated as often as required.
pleural effusions, as found with blood or pus within the pleural space, may Critical care echocardiography may be divided into basic and
be difficult to image. The dense complexity may make it difficult to differ- advanced levels. Skill at basic critical care echocardiography is a requisite
entiate pleural fluid from underlying consolidated lung, and the chest wall skill for the frontline intensivist. It is easy to learn and has immediate
interface may be unclear. Chest CT is needed in this situation. bedside utility. Advanced-level echocardiography requires extensive
A major application of pleural ultrasonography is to guide thoracen- training that is similar in scope to that required in cardiology training
tesis. This has utility for the intensivist who needs to insert a pleural with the addition of training in aspects of cardiac ultrasonography that
drainage device into the patient receiving mechanical ventilation. In this are not in the standard cardiology curriculum. This level of training
population, inadvertent laceration of the visceral pleural surface may may not have much utility for the intensivist, nor is it needed for rapid
result in tension pneumothorax. The goal is simple: to identify a safe site, assessment of hemodynamic failure. The concept of basic-level training
angle, and depth for needle penetration into the pleural fluid. Needle has been supported in recent statements from the critical care and emer-
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insertion may be followed by simple aspiration of fluid in a quantity gency medicine specialties.
insert a larger catheter for definitive drainage, or used to pass a wire for ■ BASIC CRITICAL CARE ECHOCARDIOGRAPHY
sufficient for diagnostic testing. Alternatively, the needle may be used to
insertion of a chest tube of whatever size that is indicated using modified Basic critical care echocardiography allows the intensivist to rapidly assess
Seldinger technique. cardiac anatomy and function in the patient who is hemodynamically

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