Page 303 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 29: ICU Ultrasonography 207

unstable. The examination typically includes five standard views: para- with ultrasonography. Following standard site preparation, the needle/
sternal long axis (PSLA), parasternal short axis midventricular level syringe assembly is inserted at the indicated site at an angle defined by
(PSSA), apical four chamber (AP4), subcostal long axis (SC), and infe- the transducer. A wire is passed into the pericardial space followed by an
rior vena cava long axis (IVC). Color Doppler may be used to check for appropriate catheter. Catheter position may be documented by injection
severe valvular regurgitation, but the examination does not include use of agitated saline.
of spectral Doppler. The goal is to categorize shock state and to develop Cardiac ultrasonography can be used during resuscitation from car-
an immediate management plan based upon the visual qualitative assess- diac arrest. While chest compressions are underway, the transducer is
ment of cardiac anatomy and function. prepositioned for an SC view. During pulse checks, the examiner has
The PSLA and PSSA are useful for the assessment of left ventricular several seconds to assess cardiac function. Under no circumstances should
(LV) and right ventricular (RV) size and function, major valve abnor- the examination be prolonged beyond that required for pulse check, as
mality, septal dynamics, and pericardial effusion. The AP4 view is used uninterrupted chest compressions are the mainstay of cardiopulmonary
specifically to identify RV dilation. The SC view is often the only inter- resuscitation (CPR). This requires the examiner to be proficient in quick
pretable view in the patient on ventilatory support, so that it is either a assessment of cardiac function. The goal is to identify reversible causes
confirmatory view or the only means visualizing cardiac function. The for the arrest such as pericardial tamponade, profound hypovolemia,
IVC view is used to identify the volume responsive patient. or an acutely dilated RV. The heart may show contractile function even
The information derived from the limited cardiac ultrasonographic though there is no palpable pulse. Without cardiac ultrasonography, the
examination is used to categorize the shock state. A consequential pericar- patient would be labeled as having pulseless electrical activity. In this situ-
dial effusion with RV compression pattern may require urgent intervention ation, further resuscitation effort may be worthwhile. On the other hand,
with ultrasound-guided pericardiocentesis. A hypocontractile RV that is complete absence of cardiac activity on echocardiographic examination
larger in size than the LV in AP4 view suggests acute cor pulmonale, and during a CPR event portends a dismal prognosis for recovery, and war-
requires consideration of pulmonary embolism or other cause for acute rants discontinuation of the resuscitation attempt. 41,42
or chronic RV failure. Severe LV dysfunction suggests cardiogenic origin ■
for the hemodynamic failure, while major valve abnormality may explain ADVANCED CRITICAL CARE ECHOCARDIOGRAPHY
the shock state. Severe hypovolemic shock is identified by the presence of Competence in advanced critical care echocardiography allows the
end systolic effacement of the LV cavity and a very small or virtual IVC. intensivist to perform a comprehensive hemodynamic assessment of
A frequent question in management of shock pertains to whether the cardiac function. In addition to being skilled in all aspects of standard
patient will benefit from further volume resuscitation. If the patient is on cardiology-type echocardiography, the intensivist is able to measure
ventilator support and fully adapted to the ventilator, variation in IVC size stroke volume, cardiac output (and all derived values), and intracardiac
between inspiration and expiration is an indicator of preload sensitivity. 37,38 pressures including qualitative estimates of LV filling pressure. This
The finding of normal cardiac function is also useful, as it suggests dis- training level typically includes full training in transesophageal echo-
tributive shock. Beyond the possibility of categorizing shock state, the cardiography, which has particular utility in management of the patient
findings allow the intensivist to direct therapeutic response guided by the with inadequate transthoracic windows.
echocardiographic findings. The study may be repeated as often as needed Compared to basic level, training to advanced level is challenging and
to follow response to therapy as well as evolution of disease. time consuming. In the United States, a typical approach would be to
Basic critical care echocardiography can be mastered in a relatively fulfill the requirements for competence in echocardiography as defined
short period of time. However, the intensivist needs to cognizant by the national cardiology societies. The intensivist should consider
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3
of the pitfalls of the technique. Problems with image acquisition and taking the echocardiography boards in order to provide definitive evi-
interpretation require careful attention to scanning axis and transducer dence of skill in the field.
position. In the PSLA view, minimal off axis scanning will yield a false
finding of end systolic effacement. Overrotation in the PSSA view will Vascular Diagnostic: Intensivists and emergency medicine physicians
result in a false finding of septal flattening from RV volume overload. In can use ultrasonography for diagnosis of deep vein thrombosis with an
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the AP4 view, counterclockwise rotation of the transducer will cause an accuracy that is similar to radiological study. Definitive skill at DVT
enlarged RV to appear to be normal sized. The patient who is tachypneic study requires only a few hours of training, and the examination takes
or on ventilator support will have major cardiac displacement with each only a few minutes to perform. The ability to rapidly assess for DVT at
breath. This may alter the tomographic scanning plane during echocar- the bedside of the patient with unexplained dyspnea or shock without
diography. Hyperinflation of the lungs, body habitus, or chest dressings having to wait for a radiology supported study has major advantage,
may degrade image quality. Training and experience are the only solu- given that thromboembolic disease is a common concern in the ICU.
tion to these problems of image acquisition and interpretation. The examination for DVT is performed using a vascular transducer
It is common for the patient in shock to have multiple abnormal with two-dimensional imaging; no Doppler is required. The target
findings on screening echocardiography. Some may derive from chronic vessel is examined in transverse axis for the presence of visible clot. If
disease, some from the acute illness; there may several causes for the none is observed, the vessel is compressed with the transducer. A visible
shock state. For example, severe sepsis may be associated with hypovo- clot or lack of compressibility of the vein is diagnostic of a DVT. The
lemia, LV dysfunction, and vasomotor failure. The intensivist must have common femoral, proximal superficial femoral, and popliteal veins are
the cognitive background to apply the ultrasound results to a complex examined bilaterally at multiple sites. The axillary and internal jugular
clinical situation. vein may be examined in similar fashion. The subclavian vein is diffi-
Another key element of basic critical care echocardiography is that cult to compress, and so the examination may not yield reliable results.
intensivists must have a clear understanding of the limitations of their Obesity, edema, femoral venous access, and wounds may preclude
skill level. Segmental wall analysis, detailed analysis of valve anatomy adequate examination.
and function, evaluation for endocarditis, or measurement of cardiac Abdominal Ultrasonography: The frontline intensivist does not need
pressures and flows are beyond the capability of the basic-level echocar- to have advanced-level competence in abdominal ultrasonography.
diographer. The intensivist needs to know when to call for the advanced- Instead, the focus should be on a limited approach. Specific skills of
level echocardiographer. interest to the intensivists include the following:
Pericardiocentesis for pericardial tamponade is best performed with
ultrasonographic guidance. The skill set required for ultrasound- 1. Identification of ascites: Ascites appears as a relatively hypoechoic
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guided pericardiocentesis is identical to that required for thoracentesis. space subtended by typical anatomic boundaries (the abdomi-
The best site, angle, and depth for needle penetration are determined nal wall and intra-abdominal organs) in association with typical

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