Point-of-care ultrasound has become an essential part of pediatric emergency medicine training and practice. It can have significant clinical benefits, including improving diagnostic accuracy and decreasing length of stay, and does not require radiation exposure for patients. In this review, we summarize the current diagnostic point-of-care ultrasound applications in pediatric emergency medicine, their evidence, and techniques.
Key points
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Point-of-care ultrasound is an essential part of pediatric emergency training and practice.
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Point-of-care ultrasound can decrease lengths of stay, decrease radiation exposure, and improve patient satisfaction.
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There are a variety of different diagnostic applications for point-of-care ultrasound in pediatric emergency medicine, which have varying levels of evidence.
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Understanding the evidence and techniques for point-of-care ultrasound applications, can assist providers in using point-of-care ultrasound in their clinical practice.
Introduction
Point-of-care ultrasound (POCUS) is performed by the clinician at the bedside and is a growing skill that improves diagnostic accuracy, , decreases emergency department lengths of stay, and improves overall patient satisfaction. , POCUS is especially important to consider in the pediatric population because children are at higher risk for malignancy from ionizing radiation than adult patients. Furthermore, POCUS can be easily accessible, and imaging resolution in children is often adequate owing to smaller body habitus. POCUS offers a rapid and dynamic assessment for life-threatening conditions and, therefore, has been recently integrated into the training of pediatric emergency medicine (PEM) fellows and as part of PEM practice. , More recently, guidelines for specific ultrasound applications for PEM fellows and faculty have been published.
In this review, we discuss the most promising POCUS diagnostic applications per expert consensus. , We discuss the following applications: Extended-Focused Assessment with Sonography in Trauma, cardiac, inferior vena cava (IVC), bladder, renal, gallbladder and biliary, pelvic obstetrics, pelvic gynecology, and pediatric abdomen—intussusception, appendicitis, and pyloric stenosis, pulmonary, ocular, and testicular. A companion review on the procedural applications of POCUS in PEM discusses further applications focusing on procedural applications.
Discussion of point-of-care ultrasound applications
Pediatric Focused Assessment with Sonography for Trauma and Extended-Focused Assessment with Sonography for Trauma
Focused Assessment with Sonography for Trauma (FAST) is a series of thoracoabdominal ultrasound views performed in conjunction with the primary trauma survey to rapidly identify pericardial, plural, and peritoneal free fluid (hemorrhage). FAST has been integrated into the routine care of the injured adult and is associated with improved patient outcomes. However, the literature base, diagnostic accuracy, and usefulness of FAST in children with blunt torso trauma are inconsistent and lead to variable practice patterns. A single-center randomized trial of FAST compared with usual practice showed no decrease in computed tomography (CT) scan use. However, other reports suggest that FAST integrated into routine care can aid in the diagnosis and screening of children with blunt trauma, including the FAST-Enhanced physical examination.
FAST is performed with a low-frequency transducer in 3 abdominal ultrasound views, including the right upper quadrant ( Figs. 1 and 2 ), left upper quadrant, and suprapubic views, as well as at least 1 pericardial view, subxiphoid or parasternal long axis. The right upper quadrant view is most sensitive in older children, whereas the suprapubic view may be more sensitive in prepubertal children. Regardless, each view requires a careful inspection for anechoic free fluid by performing a thorough sweep of pediatric-specific critical anatomic landmarks. On abdominal upper quadrant views, pleural effusion (hemothorax) is recognized as free fluid or the lack of mirror image artifact. Similarly, intra-abdominal hemorrhage is identified by inspecting each of the following anatomic spaces: hepatorenal, splenorenal, inferior diaphragmatic recess, inferior liver edge, and posterior bladder. To further improve the accuracy of the study, providers may consider performing FAST serially. Extended-FAST includes evaluating pneumothorax, which includes pleural sliding using a high-frequency transducer between air-dependent rib spaces on both thoracic spaces. In younger children, traumatic pneumothorax is a rare finding, but the provider could evaluate the thorax for pulmonary contusion as represented by asymmetric or focal B-lines on pulmonary evaluation.
Pediatric Cardiac and Inferior Vena Cava
Focused cardiac ultrasound (FOCUS) seeks to identify common and life-threatening pediatric disease processes using a directed evaluation of the cardiac structures. The FOCUS does not supplant comprehensive echocardiography but offers a rapid bedside assessment for pertinent and life-threatening disease processes. The literature on FOCUS in children is limited, but in conjunction with adult patient literature, pediatric FOCUS shows usefulness for diagnosing pericardial effusion and impending cardiac tamponade, categorizing global cardiac systolic function, assessing intravascular volume status, and dynamically gauging physiologic responses to acute therapies and interventions including those offered for shock and cardiac arrest. The standard FOCUS views are performed with a low-frequency phased array transducer and include the subxiphoid, parasternal long axis, parasternal short axis, apical four-chamber, and IVC from the subxiphoid longitudinal plane.
A FOCUS assessment for cardiac arrest should include at least 2 cardiac views. However, it can be challenging to identify a heart in asystole. The use of agitated saline intravenously may improve the yield in identifying the right side of the heart. Pericardial effusion is best identified in the subxiphoid or parasternal long axis views. The most common pericardial effusion mimics are the nondependent anterior pericardial fat pad and pleural effusions, which do not track between the heart and descending thoracic aorta ( Fig. 3 ). If a pericardial effusion is identified, FOCUS can be used for further assessment for impending cardiac tamponade using dynamic parameters, including IVC assessment. IVC plethora suggests impending or concurrent pericardial tamponade. Each FOCUS view contributes to the cardiac functional assessment, including the global assessment of systolic function. Global left ventricular function can be estimated as usual, moderate, or severely decreased. Metrics, such as the E-point septal separation, have shown promise in adult FOCUS, but are not confirmed in children. Foreshortening may distort the typical appearance of the left ventricle ,leading to inaccurate assessments. Dynamic assessment of the IVC can be performed and monitored through respiratory variation. Early literature suggests the IVC/aortic ratio may be a more objective cutoff for volume assessment. A cutoff of IVC/aorta ratio of less than 0.8 has been suggested for assessment of pediatric dehydration; however, the accuracy of this cutoff as well as of POCUS IVC/aorta ratio for assessment of pediatric dehydration is still under debate FOCUS performed dynamically and in real-time may alter therapeutics intervention; for example, if the IVC remains collapsible during initial emergency resuscitation, the provider may choose to give intravenous volume over starting a vasopressor agent.
Bladder
One of the first PEM POCUS applications studied and commonly used in the pediatric emergency department is measuring the bladder’s size before catheterization in children. A bladder index (defined as a product of the anteroposterior and the transverse diameters) of 2.4 cm 2 or greater predicts success for urinary catheterization in children less than 2 years of age. Furthermore, using POCUS to measure bladder volume helps to avoid repeat catheterization and increases caregiver satisfaction. A POCUS for bladder volume also decreases time to radiology-performed transabdominal pelvic ultrasound.
Typically, a low-frequency probe (curvilinear or phased array) is fanned while positioned over the pelvis to examine the bladder in both transverse and sagittal views ( Figs. 4 and 5 ). Measurements can be taken of the bladder in different dimensions to calculate an estimated bladder volume.
Renal
POCUS in adult patients has been shown to have modest diagnostic accuracy for the diagnosis of nephrolithiasis. However, the use of POCUS for pediatric renal pathology such as obstructive uropathy remains an area of debate. Studies have shown that radiology-performed ultrasound is not as accurate as a CT scan for diagnosing pediatric urolithiasis. , However, there are noted benefits of ultrasound over a CT scan, including the lack of ionizing radiation. Thus, there is practice-dependent variation in imaging for renal pathology.
There are case reports of POCUS being used in pediatric and adolescent patients to identify urolithiasis and avoid CT radiation. Still, more research is required to assess the accuracy of POCUS for this use in children and adolescents.
When used for diagnosing nephrolithiasis, ultrasound is typically used to identify secondary signs, such as hydronephrosis, which is demonstrated by dilating the renal collecting system rather than visualizing the stone itself ( Figs. 6 and 7 ). Often, a stone cannot be visualized on ultrasound, although occasionally a twinkling artifact may be noted or the lack of ureteral jet, which can indicate a stone. Additionally, case reports exist with POCUS being used to diagnose renal infections and other pathology.
Typically, a low-frequency probe (curvilinear or phased array) is positioned in the midaxillary region to examine the kidney in both a longitudinal and transverse view. The left kidney is more cephalad and posterior compared with the right kidney. The spleen provides a smaller acoustic window compared with the liver, which can lead to more difficult visualization, and tilting the probe in between the rib spaces or having patients take a deep breath to depress the diaphragm may help to improve visualization.
Gallbladder and Biliary
Although biliary pathology is overall rare in children, the incidence of cholecystitis is rising in the setting of the obesity epidemic. A systematic review of adult patients showed the pooled estimates for sensitivity and specificity for POCUS for cholelithiasis were high: 89.8% (95% confidence interval [CI], 86.4%–92.5%) and 88.0% (95% CI, 83.7%–91.4%), respectively. There are case reports of POCUS imaging being used to diagnose cholelithiasis in pediatric patients as young as neonates. , However, data on its diagnostic accuracy in the pediatric population are lacking.
A low-frequency probe is used to perform various approaches to image the gallbladder, including the subcostal sweep (where the probe is moved along the right costal margin from medial to lateral), the lateral approach (where the probe is placed laterally on the upper right abdomen similar to a FAST approach, but then tilted anteriorly to view the gallbladder), or the X minus 7 approach (where the probe is placed either 7 cm to the right of the xiphoid process or at the midclavicular line in smaller patients) , to visualize the gallbladder. The gallbladder can then be assessed for hyperechoic stones with shadowing and biliary sludge ( Figs. 8 and 9 ). The anterior wall thickness and common bile duct can also be measured. Standard measurements are typically derived from adult measurements (3 mm for gallbladder wall for adults and 4 mm common bile duct for adults <40 years old) as standard measurements for gallbladder/biliary POCUS for pediatric and neonatal patients are unclear. Secondary signs of inflammation or infection include pericholecystic fluid and Murphy’s sign.
Pelvic and Obstetric
Ultrasound has typically been first-line in the evaluation of obstetric complaints. POCUS for first trimester intrauterine pregnancy has been shown to decrease the length of stay, , , have high diagnostic accuracy, , and be cost effective in reproductive age patients with pelvic pain and vaginal bleeding. POCUS of the abdomen and pelvis can also assist with the rapid diagnosis of a ruptured ectopic pregnancy and decrease the time to therapeutic intervention.
The uterus and adnexa can be evaluated by transabdominal or transvaginal POCUS. The transabdominal approach uses a low-frequency transducer, and a full bladder is preferred to allow for an acoustic window and improved image resolution. In the transvaginal approach, an empty bladder is preferred. The transvaginal approach is typically preferred during earlier stages of the pregnancy. A beta human chorionic gonadotropin discriminatory level of 2000 milli-international units/mL for a transvaginal ultrasound and 6500 milli-international units/mL for transabdominal ultrasound has been described, but there is a variation in the level of beta human chorionic gonadotropin across pregnancies for each gestational age, and the discriminatory levels are not always reliable; thus, clinical judgment must also be used.
When performing POCUS for an intrauterine pregnancy, the uterus should be evaluated in 2 planes, the transverse and longitudinal, in transabdominal and transvaginal approaches to identify an intrauterine pregnancy. A yolk sac in the uterus is considered to be the earliest sign of confirmed intrauterine pregnancy on POCUS because it is possible to confuse a gestational sac (part of normal early embryonic development) with a pseudogestational sac (which can occur with an ectopic pregnancy). If no yolk sac or fetus is visualized in the uterus, the pregnancy is considered an ectopic until proven otherwise in a pregnant patient. Free fluid in Morison’s pouch predicts the need for operative intervention in patients with suspected ectopic pregnancy. For intrauterine pregnancies, POCUS can also be used to determine the fetal heart rate and estimate the gestational age ( Fig. 10 ).
Pelvic and Gynecologic
Radiology-performed ultrasound is commonly used to evaluate nonpregnant female patients with pelvic complaints. It is the first line for diagnostic imaging in pediatric patients to identify pathologic processes of the uterus, adnexa, genitourinary system, and more. However, the use of a POCUS in the evaluation of pelvic pathologies is less well understood. Although there have been case reports of POCUS being used to identify ovarian torsion in the pediatric emergency department, based on ovarian size of greater than 4 cm, asymmetry compared with the other ovary, peripheralization of ovarian follicles, or lack of flow in the ovaries, additional studies are needed to understand its usefulness for this application fully. Similar to the technique for obstetric complaints, POCUS for gynecologic complaints can be performed by transabdominal or transvaginal approaches. However, transvaginal approaches are avoided in patients who are younger, premenarchal, and not sexually active.
Pediatric Abdomen: Hypertrophic Pyloric Stenosis
Hypertrophic pyloric stenosis is the most common cause of intestinal obstruction in infants presenting to the emergency department. The gold standard diagnostic study is radiology-performed ultrasound. There have been case reports of POCUS being used to diagnose hypertrophic pyloric stenosis , successfully, and more recently, an observational pilot study showed excellent diagnostic accuracy (sensitivity of 100% [95% CI, 62%–100%]) and specificity of 100% (95% CI, 92%–100%).
Typically, a wide footprint, linear transducer is used with the patient a supine or decubitus position. The subxiphoid area is first viewed, and the gastric wall is traced toward the right until the pylorus is identified in the long axis. A muscle width of greater than 3 mm or a channel length of greater than 17 mm is considered positive ( Fig. 11 ).
