Pediatric emergency medicine trisk 1123
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the adult patient, their relative clinical importance makes cardiac ultrasound an
invaluable tool when examining pediatric patients with these conditions.
Evaluating global cardiac function and volume status can also have an immediate
impact on patient care. These echocardiographic skills however, are more difficult
to acquire and beyond the scope of this chapter. Consequently, practitioners
should know their limits and use ultrasound accordingly. The purpose of focused
echocardiography is to provide the clinician with immediate bedside information
and is not meant to replace comprehensive, cardiology-performed
echocardiograms.
Numerous studies of both adult and pediatric patients have shown that
physicians can accurately identify pericardial effusions in the setting of both
traumatic and nontraumatic etiologies. In penetrating chest trauma, early
identification of pericardial effusion dramatically improves patient outcomes. In
adult patients with cardiac arrest, those with PEA who have cardiac activity
demonstrated on POCUS are more likely to survive when compared with patients
with cardiac standstill. POCUS may also identify life-threatening causes of PEA
such as cardiac tamponade. Because cardiac arrest is such a rare event in children,
prospective studies have not been performed, and single-institution investigations
may not be fruitful.
Anatomy
The standard terminology used in other ultrasound examinations is less useful
when discussing cardiac ultrasound because of the position of the heart within the
thorax. Instead, standard views are along two different cardiac planes. The
cardiac long axis views the heart along its plane from the atria to apex. The short
axis cuts across the heart from anterior to posterior, along the plane from the right
hip to the left shoulder (Fig. 131.8 ). These axes form the basis for the standard
cardiac views used in emergency POCUS.
Technique
The subxiphoid view is the same view as obtained when performing the FAST
examination. A low-frequency (2- to 5-MHz) curvilinear or phased array probe
should be chosen. Phased array probes are better for moving structures such as
the heart. Smaller footprint probes may prove useful when attempting cardiac
views between the rib spaces of pediatric patients.
FIGURE 131.8 Ultrasound axes of the heart. LA, long axis; SA, short axis.
Some controversy still exists in emergency medicine as to the direction of the
probe marker and location of the marker indicator on the monitor. We have
generally found that for the novice sonographer, keeping the marker indicator or
“dot” on the left side of the screen and marker toward the patient’s right for the
subxiphoid four-chamber view maintains consistency and convention. Classic
echocardiography dictates the opposite approach, with the probe marker directed
leftward and the marker indicator on the right side of the machine. In both
instances, the same image orientation will appear on the screen.
Recall that the heart lies obliquely in the chest, with the apex pointed toward
the left hip. The subxiphoid view cuts across the heart from its atria to apex and is
thus considered a long-axis image. The transducer position is the same as for the
cardiac portion of the FAST examination, and should lie almost parallel to the
abdomen, just below the xiphoid process with the probe angled toward the left
shoulder (Fig. 131.6 ). The probe can be slid rightward along the inferior portion
of the last rib to avoid the acoustic artifacts caused by air in the stomach, using
the liver as an acoustic window. As the ultrasound beam moves toward the left
shoulder from the subxiphoid space, it will encounter the liver first, then right
ventricle (RV) and right atrium (RA), followed by the left ventricle (LV) and left
atrium (LA). The image obtained will correlate such that the liver is at the top of
the screen and the left ventricle is near the bottom of the screen (Fig. 131.7 ).
Normally, the bright white pericardium abuts the gray myocardium. When a
pericardial effusion is present, a hypoechoic or anechoic (dark) stripe will appear
between the two (Fig. 131.9 ,
Video 131.8 ).
The left parasternal long view is obtained by placing the probe in the third or
fourth intercostal space, immediately left of the sternum, with the marker pointed
toward the left hip. Unlike the subxiphoid view in which the probe lies almost flat
against the chest, it should instead be placed perpendicular to the chest wall in the
parasternal long view (Fig. 131.10 ). The image acquired should cut across the
long axis of the heart, from the atria (right shoulder) to apex (left hip). This view
can be quite useful in obese patients, in whom the subxiphoid view is often
difficult to obtain. Just as in the subxiphoid view, the right ventricle is the first
cardiac structure encountered by the ultrasound beam, as it lies most anterior and
closest to the probe (Fig. 131.11 ,
Video 131.9 ).
FIGURE 131.9 Pericardial effusion: an anechoic fluid collection (F) surrounds the
myocardium. Note the liver (Li), right ventricle (RV), and left ventricle (LV).
The subxiphoid and parasternal long views are the most useful when assessing
for cardiac activity or pericardial effusions. Other cardiac windows include the
parasternal short view and apical four-chamber view.
The parasternal short-axis view can be obtained in a similar location on the
chest wall as for the parasternal long-axis view but with the probe oriented along
the short axis of the heart (from the patient’s left shoulder to the right hip). This
view can easily be obtained by starting in the parasternal long axis and simply
rotating the probe 90 degrees until the probe marker is pointing toward the
patient’s right hip. The image acquired in this plane gives a cross-sectional,
circumferential view of the left ventricle and, for the advanced cardiac
ultrasonographer, can be used to assess contractility ( Video 131.10 ).
