lower ribs of the thorax in the posterior axillary line to visualize the right kidney, with the indicator directed toward the patient’s head.. If views from the posterior axillary line a
Trang 1as in the case of a difficult airway patient for whom removal of the
tube and reintubation could be dangerous In this instance,
sub-costal views of the diaphragm capturing motion of each leaflet
while the patient receives positive-pressure breaths can be
per-formed (Fig 15.16) Confirmation that at least one leaflet moves
with large positive-pressure breaths will help verify that the tube
is in the airway Lack of excursion on one side might suggest
main-stem bronchus occlusion from secretions or inadvertent
main-stem bronchial intubation of the contralateral lung This
technique has been used to confirm tube placement in the
operat-ing theater49 as well as in the pediatric ED.50 In the neonatal
population the tube is visualized within the trachea in the sagittal
plane from the parasternal view typically used for evaluation of
the aortic arch and pulmonary arteries Dennington and
col-leagues were able to accurately gauge depth of ETT position in
neonates with high accuracy.51 In larger infants and older
chil-dren, this technique has not been successful owing to thoracic
growth and ossification
Airway ultrasound to visualize tracheal stenosis and appropri-ate ETT fit have also been described, though this is still an explor-atory application since it depends on successful identification of the ETT, cuff, and potential areas of stenosis using ultrasound in the air-filled trachea The accuracy of this technique is still want-ing of larger-scale population studies Some authors have de-scribed use of saline to aid in visualization, though there is the potential risk of damaging the cuff in this application.52 Airway ultrasound is readily performed at the level of the larynx or mid-trachea (Fig 15.17) with fair visualization of laryngeal structures Emerging applications for this modality, in addition to ETT siz-ing and assessment of tracheal caliber, include identification of vocal cord paresis, identification of landmarks for cricothyroid-otomy, assessment of esophageal intubation, and identification of structures for transcutaneous injection, among others.53
Use of bedside ultrasound to assess diaphragm paresis has also been described.54–58 Assessment of spontaneous diaphragm excur-sion using ultrasound in the oblique coronal (described previously)
• Fig. 15.15 Identification of pneumothorax via ultrasound. (A) Normal two-dimensional (2D) lung
ultra-soundimage.(B)CorrespondingM-modeimageto(A).(C)NotelackofB-linesinpneumothoraxin2D
image.(D)CorrespondingpneumothoraxM-modeimageto(C).
A
B
C
D
Trang 2124 SECTION II Pediatric Critical Care: Tools and Procedures
determining whether the air is within the peritoneum or in the bowel is difficult and is a limitation of abdominal ultrasonogra-phy Air localized within the liver vasculature and bowel wall hy-pervascularity have been associated with necrotizing enterocolitis
in the at-risk neonate.60–62 Similarly, fluid in the abdomen can appear within or outside the intestinal lumen The normal appearance of air artifact and stool is absent in fluid-filled ileus, resulting in ultrasound visual-ization of distended, anechoic bowel loops Peritoneal fluid as a result of ascites, hemorrhage, or peritoneal dialysis fluid is com-monly seen in acute care settings A focused assessment with so-nography in trauma (FAST) is performed in four abdominal windows where dependent fluid could appear from a traumatic injury The probe is usually a curvilinear or phased array trans-ducer The FAST examination is widely used in adult trauma re-suscitation for identification of intraperitoneal fluid, likely either from hemorrhage or ruptured viscus.63–65 Large-scale efficacy studies and meta-analyses have reduced initial enthusiasm for the test, citing inadequate specificity, operator and patient variability, and debatable impact on imaging with abdominal CT or patient outcome as major vulnerabilities In children, the sensitivity of the test is as poor as 52% in some series66; thus, its influence on changing management has been questioned.67 Meta-analyses pub-lished by the Cochrane library suggest similar concerns about the FAST examination for adult patients as well.68,69 When seen, an-echoic (dark) fluid in the abdomen may indicate intraperitoneal injury However, solid-organ injury may result in small to no de-tectable fluid It is also important to note that the diagnostic characteristics of the FAST examination in the ED are commonly performed without any elevation of the upper torso When the torso is elevated in the ICU setting, fluid will likely settle in the more dependent lower quadrants of the abdomen The FAST ex-amination is commonly referred to as the focused assessment for free fluid when fluid is suspected and assessed using ultrasound in nontrauma patients
Right Upper Quadrant ( Fig 15.18 A)
The hepatorenal recess (Morison pouch) is the most dependent part of the peritoneum in the supine patient—which, again, can change with repositioning of the patient Fluid can be seen be-tween the retroperitoneal kidney and the intraperitoneal liver or above the liver as well The transducer is placed near or below the
• Fig. 15.16 Subcostalimageofthediaphragm.(A) Asteriskindicatesthediaphragmthatisidentifiableon
M-modeimaging(B).
*
• Fig. 15.17 Laryngeal ultrasound—transverse view at the level of the
cricothyroidmembraneangledsuperiorlythroughthelarynx.Asteriskindi-catesthetruevocalcord.
or sagittal planes accurately demonstrates diaphragm paresis This
technique is also likely useful for patients with diaphragm paralysis
from a variety of causes, including protracted neuromuscular
blockade or intrinsic neuromuscular dysfunction Emerging
litera-ture also recognizes pediatric diaphragmatic atrophy with
intuba-tion and mechanical ventilaintuba-tion similar to changes seen in adult
critically ill patients.59 In adults, such changes in diaphragm
thick-ness have been associated with extubation failure and increased
mortality; such associations have not been confirmed in pediatric
patient populations
Abdominal Ultrasound
Assessment of abdominal pathology is frequently confounded by
nonspecific complaints, particularly in sedated patients
Ultra-sound as a noninvasive technology has potential for evaluating
abdominal pathology without the radiation exposure of
com-puted tomography (CT) However, as is the case with pulmonary
pathology, air within the abdominal cavity creates challenging
obstacles to ultrasound interrogation When air causes artifacts,
Trang 3lower ribs of the thorax in the posterior axillary line to visualize
the right kidney, with the indicator directed toward the patient’s
head Fluid in the Morison pouch, inferior pole of the kidney, or
the perihepatic space suggests intraperitoneal injury The
dia-phragm is also seen in this view, and pleural effusion or
intratho-racic hemorrhage in the trauma setting can also be identified or
suspected when a classic mirror artifact of the liver due to the
diaphragm is not visualized The probe is usually oriented
coro-nally but can be oriented axially with respect to the patient; thus,
the entire organ should be scanned If views from the posterior
axillary line are difficult, the right kidney can be visualized in the
anterior sagittal plane by placing the transducer at the lower edge
of the costal margin just lateral to the midclavicular line with the
indicator pointed toward the patient’s head In this view, the Morison pouch can be visualized through the liver
Left Upper Quadrant ( Fig 15.18 B)
The splenorenal recess can be visualized from the left flank at the level of the posterior axillary line as well It is visualized similarly to the view in the right, with the probe indicator po-sitioned toward the head for a coronal view of the kidney and surrounding spaces Anterior windows are usually not feasible because of stomach contents The left kidney is more cephalad
in the abdomen than the right, and views from above the costal margin may be necessary In this view, pleural effusions can also
be visualized
• Fig. 15.18 Thefocusedassessmentwithsonographyintrauma(FAST)
exam. (A) Right upper quadrant view. (B) Left upper quadrant view. (C) Longitudinaland(D)transverseviewsofthebladder.(E)Subcostalcardiac view.
C
E
D
Trang 4126 SECTION II Pediatric Critical Care: Tools and Procedures
Pelvis ( Figs 15.18 C and 15.18 D)
Particularly if a patient has been upright or inclined after trauma,
fluid can accumulate in the pelvis in a manner not seen in the
upper quadrants As with visualization of the kidneys, the bladder
can serve as an easily identifiable landmark from which to
refer-ence regional anatomy and discern pathology The bladder is
im-aged in both the axial and sagittal planes Fluid posterior to the
bladder in the male or posterior to the bladder or uterus in the
female patient suggests pathology
Subcostal Cardiac ( Fig 15.18 E)
The heart is visualized in the FAST scan from the subcostal
mar-gin below the xiphoid process, with the probe aimed toward the
patient’s left shoulder and the indicator oriented toward the right
flank if the machine remains set in a radiology convention setting
with the screen indicator to the operator’s left The heart is imaged
for pericardial effusion in this view, where dark fluid would
ap-pear adjacent to the heart
Using FAST bladder views, verification of the presence of a
urinary catheter can also be performed by visualizing the catheter
itself or the water-filled balloon of the Foley catheter A large
volume in the bladder in an anuric patient indicates obstruction
or malplacement of the urinary catheter Though several authors
have defined methods for calculating bladder volume, its variable
geometry precludes easy approximation of volume However, a
practitioner can judge whether there is urine in the bladder
de-spite efforts at diuresis or catheterization
Solid echogenic structures in the distended abdomen suggest
that the abdomen is filled with a foreign mass (tumor), enlarged
or swollen viscera, or a collection of a solidifying substance such
as exudative ascites or clotting blood Such findings should
dis-courage needle drainage of a space in the evaluation of abdominal
distention or intraabdominal hypertension unless there is also a
large volume of free fluid
In shock management evaluation of renal perfusion may be
informative as a surrogate for shock severity A marked difference
between systolic and diastolic renal arterial flow may suggest
hy-poperfusion.70,71 However, examining this phenomenon to date
has not consistently shown efficacy in evaluating shock states.72–78
Whether this assessment will prove useful in children remains to
be determined
Cardiac Ultrasound
Imaging specialists often have a wide selection of phased array
transducers for imaging the heart Large adult-sized transducers,
with more sophisticated technology and lower-frequency
trans-mission for adequate penetration, suit adolescents and young
adults well Smaller transducers allow use of slightly higher
fre-quencies for imaging infants and young children, and their
smaller faces permit better skin contact when the probe is held at
shallow angles to the skin Therefore, it is important that adequate
equipment be available for accurate bedside ultrasound cardiac
evaluation of critically ill patients
Imaging of the heart is performed using locations, or windows,
on the body where acoustic transmission to the heart is adequate
and less encumbered by effects of body position and tissue
inter-ference These include the subcostal window immediately below
the xiphoid process, the parasternal window to the left of the
pa-tient’s sternum, and the apical window near the papa-tient’s point of
maximal cardiac impulse, typically below the left pectoralis major
muscle These windows form standard echocardiography views (Fig 15.19)
Of note, different groups (i.e., cardiology, emergency medi-cine, critical care medicine) may use different screen indicator orientations during cardiac ultrasound evaluation Within the scope of this text, the screen indicator is at the top right of the screen for all cardiac views Subcostal windows can be used to visualize the base of the heart either longitudinally, such that all four chambers are seen (Fig 15.19A), or in cross-section, such that only the atria or ventricles are seen The probe is placed in the subxiphoid region and beam aimed toward the patient’s left shoulder For a longitudinal view, the probe indicator is directed toward the patient’s left flank, or approximately the 2 o’clock to 3 o’clock position with the top of the clock oriented toward the patient’s head For a transverse view, the probe indicator is di-rected at the patient’s head and the view aligned across the cham-bers of interest From the transverse view the probe can also be directed directly posteriorly through the inferior vena cava (Fig 15.19B) as it passes into the right atrium to assess its size variation through the respiratory cycle or through the aorta for evaluation of flow Any view of the heart should be more than a single image; fanning the transducer beam through the organ can provide the most complete impression of the heart Septal defects are most easily visualized from the subcostal position using Dop-pler sonography because flow across them is most parallel to the ultrasound beam In addition, the window is closest to the base of the heart and provides excellent imaging of effusion, particularly
if the patient is slightly inclined head up This window also has an advantage in small children with multiple dressings or monitoring devices on the chest because the subcostal window may be the only area not obscured
Subcostal views are also important during active resuscitation from cardiac arrest when chest compressions must have priority (see section on Cardiac Arrest) Though subcostal windows ben-efit from not having intervening lung tissue obscure the heart, they can be hindered by interference from a gas-filled stomach and/or bowel In the case of internal interference from air-filled viscera, insonating the base of the heart from a position slightly overlying the right lobe of the liver can sometimes improve the view Subcostal views may also be difficult in patients with sub-sternal chest tubes or ventricular assist devices
Views from the parasternal windows are commonly acquired from the third and fourth intercostal interspaces near the sternum
on the patient’s left chest To acquire the parasternal long-axis view (Fig 15.19C), the transducer indicator is toward the pa-tient’s right shoulder and aligned along the major axis of the left heart From this view, the left atrium, mitral valve (MV), left ventricular chamber, and left ventricular outflow tract (LVOT) are readily visible in continuity with the right ventricular outflow tract that appears anterior to the LVOT This view can be modi-fied to image the right ventricular inflow view by fanning the transducer anteriorly through the right heart The right atrium and IVC are usually visible and the tricuspid valve opens into the right ventricle anterior and caudad to the right atrium The SVC may be occasionally visualized in infants, though it is frequently obscured by the lung in an older patient
The parasternal window can also be used for visualizing the heart in a plane perpendicular to its major axis, or the short-axis view (Fig 15.19D) Short-axis views are performed with the transducer indicator aligned toward the patient’s left shoulder There are several short-axis views that span the length of the heart from atrium to apex Imaging the ventricle at the midchamber
Trang 5• Fig. 15.19
Basiccardiacviews.(A)Subcostallong-axisviewwheretheliver(1),rightven-tricle (2), and left venBasiccardiacviews.(A)Subcostallong-axisviewwheretheliver(1),rightven-tricle (3) are visible. (B) Inferior vena cava (asterisk). (C) Parasternal long-axisviewwheretheleftatrium(1),leftventricle(2),aorta(3),andrightventricularoutflow tract (4) are visible. (D) Parasternal short-axis view at the midpapillary level where the left ventricle(1)andrightventricle(2)arevisible.(E)Parasternalshortaxisattheaorticvalvelevel wheretheaorticvalve(1),tricuspidvalve(2),atrialseptum(3),andleftcoronaryarteryare visible(4).(F)Apicalfour-chamberviewvisualizingtheleftventricle (1),leftatrium(2),right ventricle(3),andrightatrium(4).
C,D,E
2 3
3 4
1
2 V
3
2
1 2
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2
3 V
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