Chapter 15: Pediatric Point-of-Care Ultrasound (P-POCUS)

• Focused assessment with sonography in trauma (FAST) in the hypotensive child allows for rapid identification of life-threatening intra-abdominal hemorrhage. In the stable traumatized child, serial FAST improves the identification of occult intra-abdominal injuries and may prove to be a useful screening tool aimed at reducing the number of computed tomography scans obtained.

• Pediatric point-of-care ultrasound (P-POCUS) allows for the more accurate identification of skin and soft-tissue infections requiring incision and drainage.

• P-POCUS improves the safety and efficiency with which central venous access is obtained in children and may improve the first-time success rate and efficiency of peripheral vascular access in children with difficult peripheral vascular access.

Pediatric point-of-care ultrasound (P-POCUS) is a skill that is enabling physicians to use ultrasound technology as an extension of the physical examination to more accurately, efficiently, and safely manage children with acute medical, surgical, and trauma-related conditions. In this chapter, an introduction to three common indications for P-POCUS will be briefly reviewed—abdominal and torso trauma, skin and soft-tissue infections, and vascular access.

The focused assessment with sonography in trauma (FAST) scan was shown to reduce time to operative care, hospital length of stay, use of computed tomography (CT) and hospital costs, as well as improved morbidity in adult trauma patients.¹ In the persistently unstable child with torso trauma, FAST similarly allows for the rapid identification and management of intra-abdominal hemorrhage². On the other hand, most children with intra-abdominal injuries do not require surgery and therefore FAST may serve a different goal. Some have studied the utility of pediatric FAST scanning in diagnosing intra-abdominal hemorrhage versus diagnosing any injury versus clinically important injuries. The difficulty is in the consistent finding that approximately 15% of patients with torso trauma, for whom trauma code activation criteria were met, and likely some of those in whom it was not, have significant occult injuries. The current gold standard is still CT scanning. When FAST is used in the stable pediatric trauma patient,³ in conjunction with other diagnostic examinations, such as physical examination,⁴ liver function test,⁵ and/or serial FAST,⁶ its performance at identifying clinically important intra-abdominal injuries improves significantly. Most likely, a clinical decision rule incorporating serial FAST will improve the sensitivity and specificity of algorithms such as that proposed by Holmes et al.⁷ thereby assuring the appropriate group of injured children have diagnostic imaging, while not missing clinically important injuries with the goal of minimizing unnecessary radiation exposure.

The FAST technique using a low-frequency curvilinear probe in pediatrics is often easier to perform compared with adults given their smaller size and more echogenic tissue. One begins by looking at the hepatorenal space (Morison's pouch) in the right upper quadrant, which is the second most dependent part of the supine abdomen and where blood from the pelvis (the most dependent part but very small in volume) and the left upper quadrant drain to and where, when hemorrhage is present, blood will be seen in approximately 85% of cases. Next, the left upper quadrant is scanned, often requiring the user to position the probe more posteriorly and superiorly to locate the splenorenal interface. This is followed by the pelvic view in which the bladder–rectum interface in boys, and bladder–uterus and uterus–rectum interfaces in girls are looked at. Finally, an abdominal view of the pericardium is done to evaluate for the presence of pericardial effusion, and can also allow one to assess whether there is a vigorous or absent cardiac activity to help guide the resuscitation efforts. By looking at these interfaces, one needs to determine whether blood is present or absent; a hypoechoic wedge (black) between the hyperechoic (white) capsules of the mentioned organs is either absent (Fig. 15-1A) or present (Fig. 15-1B–D). If one notes blood above the diaphragm in the RUQ and LUQ views, a hemothorax is identified. Although image interpretation is relatively easy, image acquisition is where most novices have difficulties.

An extension of FAST, which often proves very useful given the low sensitivity of the supine chest radiograph at excluding pneumothorax, is the assessment for lung sliding, comet tail artifacts, and lung point by placing the probe across the second and third intercostal rib space bilaterally (Fig. 15-2). It has been shown to be very sensitive at excluding pneumothorax (sensitivity 98% vs. 75% for the supine chest radiograph).⁸ More recently, some groups have advocated extending FAST to the major long bones to rapidly assess for presence of fractures to help guide management².

Clinical examination of skin and soft-tissue infections often reveal an erythematous, warm, tender, and indurated area of skin in both cellulitis and abscess. Fluctuance is not always present with an abscess and may be present with cellulitis, and often these two entities coexist leading to missed abscesses or unnecessary invasive procedures. Noteworthy was one study's finding of 30% to 50% error rates in clinical predictions of abscesses requiring drainage.⁹

P-POCUS has provided a tool that physicians can easily learn and use to help improve the diagnosis of cellulitis and abscesses. Studies confirm sensitivity in the 90% to 98% range and specificity in the 75% to 79% range.^10–12 Management decisions were changed for approximately 20% to 56% of adult patients^9,10 and 14% to 22% of pediatric patients,^11,12 including those discovered to be abscesses in need of drainage, those thought to need drainage but proven to be cellulitis, as well as those in which other diagnoses were discovered and disasters averted such as incising into a vascular malformation.

When a child presents with a skin and soft-tissue infection, the high-frequency linear probe is used to scan the area by moving the probe over the affected area in two orthogonal planes. By gently moving the probe longitudinally and then transversely, an understanding of the three-dimensional aspect of the infection is obtained. The appearance of the affected area is then compared with normal skin and soft tissue; infected soft tissue evolves from that of normal appearing skin (Fig. 15-3A) to thickened subcutaneous tissue (Fig. 15-3B) to distortion of subcutaneous tissue with inflammatory edema (cobblestoned appearance of edema between the fat lobules) to that of a more organized collection of pus that appears anechoic or hypoechoic with indiscrete or irregular borders of an abscess¹³ (Fig. 15-3C,D). The use of generous amounts of gel and application of very little pressure will minimize the discomfort to the child and ensure that superficial abscesses are not collapsed by the probe's pressure. When an abscess is seen, the “squish” sign can be appreciated by applying pressure to the area and noting the liquefied debris of an abscess moving around. By scanning in two orthogonal planes, blood vessels and abscess can also be differentiated; the abscess will be round or ovoid in both planes whereas the blood vessel will be round and longitudinal in the different planes (Fig. 15-4). Doppler ultrasound can be used to assess flow within the abscess as it should be absent (Fig. 15-4, inset); its presence suggests the presence of a blood vessel or if seen within the center of the hypoechoic area suggests a lymphatic structure. Finally, one can guide the incision and drainage or the needle aspirate under direct visualization or by marking out the area of interest and noting the depth.

Difficult vascular access is often the rate-limiting step in resuscitation of children. Although intraosseous access may serve as a bridge to vascular access, it is temporary. P-POCUS improves the success of placement of both peripheral and central venous catheters.

By using the high-frequency linear probe, one identifies the vessel of interest and its surrounding relationships.¹⁴ The vein should be compressible, nonpulsatile, and increase with valsalva or positioning maneuvers that increase venous pooling. The use of real-time guidance of the vascular access procedure is the preferred method, ideally with one-operator technique such that fine adjustment of the probe can be made as the catheter is being inserted. However, the static view or two-operator techniques are better than landmark or blind techniques if operators are not yet adept at one-operator real-time ultrasound guidance.¹⁵

Central Venous Access

When a central line is needed, the femoral vein is the most apparent candidate as it is away from the neck or chest where other life-saving maneuvers may be in progress, such as cervical spine immobilization, securing the airway, or chest compressions. The traditional technique of palpating the femoral artery and inserting the needle medial to this to access the femoral vein can be unreliable. By using ultrasound to guide central venous access, numerous adult studies have demonstrated that it improves time to cannulation, first-time success rate, while decreasing complications of arterial punctures and failure to cannulate the vein.^15,16 Acronyms describing the medial to lateral relationship of vein, artery, and nerve (Fig. 15-5A) have been demonstrated to be inconsistent. The femoral artery and vein overlap in 12% to 45% of children^17,18 and in up to 88% of children just 1 cm distal the inguinal ligament in the frog-legposition¹⁸ (Fig. 15-5B). Another study demonstrated faster and safer femoral vein catheterization using ultrasound during cardiopulmonary resuscitation (CPR) in adults.¹⁹ In particular, they noted that the pulsations felt in the groin during CPR was venous in origin.

Peripheral Venous Access

Peripheral intravenous (IV) placement is one of the most common and distressing procedures performed in pediatric hospitals, often being the leading sources of pain during their ED visit. POCUS can be used to visualize and guide peripheral IV placement. Studies to date have yielded mixed results.^20,21 However, when performed by ED nurses in an adult population with difficult IV access, it led to an improved success rate and fewer complications,^22,23 as well as improved patient satisfaction.²⁴

In one study, children with difficult venous access were randomized to an ultrasound group, in which the vein was visualized and marked by a physician through which the nurse would attempt the IV, but there was no significant benefit demonstrated with this static, two-operator–based technique.²⁵ Subsequently, Doniger et al.²⁶ studied whether two-operator real-time ultrasound-guided IV placement resulted in improved success in children. The physician performed the ultrasound visualization of the vein and the nurse performed the IV catheterization and resulted in reduced time to successful IV placement and fewer numbers of skin punctures. More recently, one-operator real-time ultrasound-guided IV placements among children less than 3 years old with difficult IV access undergoing general anesthesia was performed in which the use of ultrasound resulted in a shorter time to IV placement (seven times faster) compared with traditional technique, along with fewer skin punctures and a higher first-attempt success rate.²⁷ An adult ED study demonstrated that an ultrasound-guided peripheral IV access program significantly reduced the number of central venous catheters placed in the ED, particularly in noncritically ill patients.²⁸ Another study similarly demonstrated that nurse-performed ultrasound-guided IV placements led to significant improvements in patient care and fewer physician vascular access interventions.²⁴ A meta-analysis of IV placement in difficult IV access patients confirmed that ultrasound more than doubled the likelihood of successful cannulation.²⁹

Because peripheral veins are easily compressible, pressure is minimized by applying generous amounts of sterile gel. The larger peripheral veins located between 0.3 and 1.6 cm deep are those that will be cannulated most successfully with ultrasound guidance (Fig. 15-6).³⁰ Maneuvers such as blood pressure cuff or tourniquet application can increase the size of the vein to improve the likelihood of success.³¹

P-POCUS is an expanding skill in the hands of frontline pediatric emergency medicine physicians with many novel applications underway. For instance, musculoskeletal applications are among the upcoming most promising additions to the armamentarium of physicians managing children with injuries to the extremities; its use will help rapidly diagnose pediatric fractures, guide closed reductions of displaced long bones, as well as confirm the presence or absence of joint effusions in both traumatic and nontraumatic conditions.