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CHAPTER 15  Ultrasonography in the Pediatric Intensive Care Unit A C B D 123 • Fig 15.15  ​Identification of pneumothorax via ultrasound (A) Normal two-dimensional (2D) lung ultrasound image (B) Corresponding M-mode image to (A) (C) Note lack of B-lines in pneumothorax in 2D image (D) Corresponding pneumothorax M-mode image to (C) as in the case of a difficult airway patient for whom removal of the tube and reintubation could be dangerous In this instance, subcostal views of the diaphragm capturing motion of each leaflet while the patient receives positive-pressure breaths can be performed (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 operating 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 colleagues were able to accurately gauge depth of ETT position in neonates with high accuracy.51 In larger infants and older children, this technique has not been successful owing to thoracic growth and ossification Airway ultrasound to visualize tracheal stenosis and appropriate ETT fit have also been described, though this is still an exploratory 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 wanting of larger-scale population studies Some authors have described 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 midtrachea (Fig 15.17) with fair visualization of laryngeal structures Emerging applications for this modality, in addition to ETT sizing and assessment of tracheal caliber, include identification of vocal cord paresis, identification of landmarks for cricothyroidotomy, 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 excursion using ultrasound in the oblique coronal (described previously) 124 S E C T I O N I I   Pediatric Critical Care: Tools and Procedures * B A • Fig 15.16  ​Subcostal image of the diaphragm (A) Asterisk indicates the diaphragm that is identifiable on M-mode imaging (B) • Fig 15.17  ​Laryngeal ultrasound—transverse view at the level of the cricothyroid membrane angled superiorly through the larynx Asterisk indicates the true vocal cord 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 literature also recognizes pediatric diaphragmatic atrophy with intubation and mechanical ventilation similar to changes seen in adult critically ill patients.59 In adults, such changes in diaphragm thickness 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 Ultrasound as a noninvasive technology has potential for evaluating abdominal pathology without the radiation exposure of computed 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, determining whether the air is within the peritoneum or in the bowel is difficult and is a limitation of abdominal ultrasonography Air localized within the liver vasculature and bowel wall hypervascularity 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 visualization of distended, anechoic bowel loops Peritoneal fluid as a result of ascites, hemorrhage, or peritoneal dialysis fluid is commonly seen in acute care settings A focused assessment with sonography 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 transducer The FAST examination is widely used in adult trauma resuscitation 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 published by the Cochrane library suggest similar concerns about the FAST examination for adult patients as well.68,69 When seen, anechoic (dark) fluid in the abdomen may indicate intraperitoneal injury However, solid-organ injury may result in small to no detectable 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 examination 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 15.18A) 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 between the retroperitoneal kidney and the intraperitoneal liver or above the liver as well The transducer is placed near or below the CHAPTER 15  Ultrasonography in the Pediatric Intensive Care Unit A B C D 125 • Fig 15.18  ​The focused assessment with sonography in trauma (FAST) E lower 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 diaphragm is also seen in this view, and pleural effusion or intrathoracic 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 coronally 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 exam (A) Right upper quadrant view (B) Left upper quadrant view (C) Longitudinal and (D) transverse views of the bladder (E) Subcostal cardiac view indicator pointed toward the patient’s head In this view, the Morison pouch can be visualized through the liver Left Upper Quadrant (Fig 15.18B) 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 positioned 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 126 S E C T I O N I I   Pediatric Critical Care: Tools and Procedures Pelvis (Figs 15.18C and 15.18D) 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 reference regional anatomy and discern pathology The bladder is imaged 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 15.18E) The heart is visualized in the FAST scan from the subcostal margin 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 appear 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 despite 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 discourage 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 hypoperfusion.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 transmission for adequate penetration, suit adolescents and young adults well Smaller transducers allow use of slightly higher frequencies 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 interference These include the subcostal window immediately below the xiphoid process, the parasternal window to the left of the patient’s sternum, and the apical window near the patient’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 medicine, 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 o’clock to o’clock position with the top of the clock oriented toward the patient’s head For a transverse view, the probe indicator is directed at the patient’s head and the view aligned across the chambers 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 Doppler 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 benefit 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 substernal 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 patient’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 modified 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 * A B 2 1 C D V 4 E F C,D,E A,B F • Fig 15.19  ​Basic cardiac views (A) Subcostal long-axis view where the liver (1), right ven- tricle (2), and left ventricle (3) are visible (B) Inferior vena cava (asterisk) (C) Parasternal long-axis view where the left atrium (1), left ventricle (2), aorta (3), and right ventricular outflow tract (4) are visible (D) Parasternal short-axis view at the midpapillary level where the left ventricle (1) and right ventricle (2) are visible (E) Parasternal short axis at the aortic valve level where the aortic valve (1), tricuspid valve (2), atrial septum (3), and left coronary artery are visible (4) (F) Apical four-chamber view visualizing the left ventricle (1), left atrium (2), right ventricle (3), and right atrium (4)  ... pulmonary pathology, air within the abdominal cavity creates challenging obstacles to ultrasound interrogation When air causes artifacts, determining whether the air is within the peritoneum or in... localized within the liver vasculature and bowel wall hypervascularity have been associated with necrotizing enterocolitis in the at-risk neonate.60–62 Similarly, fluid in the abdomen can appear within... suggest hypoperfusion.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