Central Line Positional Assessment With Ultrasonography

When caring for critically ill neonates, obtaining adequate venous access is of crucial importance. In the neonatal intensive care unit, the 2 most commonly used central venous catheters are peripherally inserted central catheters (PICCs) and umbilical venous catheters (UVCs). Ideally, these catheters traverse through the peripheral venous circulation, reaching central termination just outside of the right atrium at either the superior or inferior cavoatrial junction. Assessing this line position at the time of placement is of utmost importance to minimize risks associated with malposition. Additionally, performing periodic surveillance can be helpful to detect migration of these catheters. Traditionally, plain film radiography has been used to assess line tip position. However, point-of-care ultrasonography performed by neonatal clinicians has emerged as an attractive alternative with many distinct advantages.1In this article, we summarize how point-of-care ultrasonography can be used in the assessment of these catheters. In Video 1, we introduce the probes used for these assessments and review some ultrasonography screen conventions. We highlight imaging windows through which upper extremity PICCs, lower extremity PICCs, and UVCs can be visualized. Video 1 also demonstrates clips of well-positioned and malpositioned catheters, along with techniques to troubleshoot malpositioned catheters.Plain film radiography is largely available in most neonatal intensive care units, but several disadvantages of this modality exist. Depending on the unit and the time of day, there can be lengthy time delays in the completion of this study.2 Unless there is access to fluoroscopy, plain film radiography is a static assessment. This often necessitates obtaining multiple radiographs as a line is adjusted,3 with the potential for this exposure to radiation to pose a cumulative risk. Plain film radiography also uses nonvascular landmarks, such as bones, to approximate appropriate line termination targets. There is a strong body of evidence that suggests line positioning with plain film radiography results in a significant number of malpositioned catheters.4–6 Complications secondary to malpositioned central lines can be catastrophic, with examples of these being infusate extravasation, pleural effusion, and pericardial effusion.Point-of-care ultrasonography is a tool available to neonatal clinicians that allows for central line position to be assessed at the bedside in real time. The biggest advantage of this modality is that the line termination can be compared directly to actual vascular landmarks as opposed to relying on nonvascular surrogates that give an estimation as to where true anatomic landmarks lie. This line assessment with ultrasonography is dynamic, which can be useful when adjusting lines or to investigate if line position is changing secondary to patient positioning (such as with extremity flexion or extension).1,7 This modality is also radiation free, allowing for frequent interrogation of line positioning without this potential risk to the patient.To assess central line position with ultrasonography, an ultrasonography machine is necessary. Although there are many machines available on the market, this investigation requires the most basic functionalities shared by all these devices. A more important equipment consideration is probe selection. The 2 most common probes used for central line assessment are phased array probes and large footprint linear probes. Phased array probes are used for a variety of different applications, with one of the most common being cardiac imaging. These probes are typically lower frequency with high penetration, allowing for imaging of deeper structures with relative ease. Large footprint linear probes are typically higher frequency, providing excellent resolution, sometimes at the expense of poor penetration, which is less often an issue in neonates, given their smaller size. It is important to familiarize oneself with how to adjust depth and gain on the ultrasonography machine because these settings must be optimized with each study to produce interpretable images.Lower extremity PICC lines are the simplest and most straightforward central venous catheters to image; therefore, they represent the starting point for providers interested in learning this important skill. Lower extremity PICCs are inserted into the greater saphenous vein, lesser saphenous vein, popliteal vein, or femoral vein. After traversing through the distal lower extremity vasculature, the PICC reaches the iliac vein before entering the inferior vena cava. This large, central vessel navigates just behind the liver; this organ can be used as a sonographic window to produce images that are strikingly simple to interpret. Either the phased array probe or the large footprint linear probe can be used for this application. To image a catheter in this position, the probe is placed subxiphoid, in a sagittal orientation, with the probe marker pointed toward the patient’s head (Figure 1A). If successful, the intrahepatic inferior vena cava will come into view, with drainage of this vessel into the right atrium readily visible (Figure 1B). Optimal termination of this catheter is with the tip just below the inferior cavoatrial junction. An alternative window that can be used is through the right lateral flank (Figure 2), which may be a superior window in some patients, especially those with severe abdominal protuberance, an abdominal wall defect, or abundant bowel gas or in patients with overlying dressings or other obstructions to scanning in the subxiphoid area.Upper extremity PICC lines are substantially more challenging to image by point-of-care ultrasonography because of the lungs and ribs that lie in close proximity to the ultrasonography window that may narrow the view. Ultrasonography beams cannot penetrate air, with attempts at this resulting in beam reverberation and subsequent artifact. Bones generate similar artifacts and obstructions to ultrasonography beams. Conveniently, the bones of many neonates are incompletely ossified, making this more of an issue in older infants and children; however, to obtain the clearest images possible, the sternum and rib spaces may still need to be navigated even in small neonates. Upper extremity PICCs are inserted into the basilic vein, cephalic vein, brachial vein, or axillary vein. These lines eventually reach the brachiocephalic vein before entering the superior vena cava. Typically, the phased array probe is used to image lines in this position using modified cardiac views. This probe is oriented sagittally, with the probe marker pointed toward the patient’s head in a high parasternal view just in the middle of the sternum (Figure 3A). Small adjustments to the right or left are required to navigate the lung artifact interfering with the view. The superior vena cava lies rightward and just behind the ascending aorta, and it is brought into view by visualizing first the ascending aorta followed by tilting the ultrasonography beam to the patient’s right. Fine probe adjustments are necessary to visualize this structure draining into the right atrium, with optimal catheter termination being within the superior vena cava just above the superior cavoatrial junction (Figure 3B). If unable to visualize the superior vena cava in this window because of lung artifact, other cardiac views such as the subcostal view or the right ventricle inflow view can be used to image the right atrium to assess for deep line termination (Figure 4). An additional application of ultrasonography for upper extremity PICC placement is to troubleshoot lines that malposition within the neck vasculature, typically into the internal jugular vein. A linear probe is preferred for this technique. If a line is visualized within this vessel, it can be retracted under direct visualization. Focal pressure to the internal jugular vein can then be briefly applied to occlude the vessel, thus encouraging the line to turn into central termination. Care should be taken to ensure this occlusion is as brief as possible, and application of pressure should not be so firm as to result in arterial compression or airway occlusion.UVC line tips can also be challenging to image. This is secondary to the meandering path these lines take as they traverse through the umbilical vein, into the liver across the portal confluence, and through the ductus venosus before achieving final termination just below the inferior cavoatrial junction. Similar to lower extremity PICCs, either the phased array probe or the large footprint linear probe can be used to image these lines. Probe positioning begins similarly to that used for lower extremity PICC visualization, although it typically requires the probe to be slid to the patient’s right, rotated slightly counterclockwise, and fanned slightly to the patient’s right (Figure 5A).8,9 These probe adjustments can differ widely from patient to patient because of variability in anatomy. If successful, the line can be seen going through the portal confluence, entering the ductus venosus, and terminating within the inferior vena cava (Figure 5B).When performing central line positional assessments with ultrasonography, it is critically important to ensure the catheter and its tip are definitively seen. Central lines appear as mobile, echo-bright structures, usually having the appearance of 2 parallel lines running alongside each other. It is very easy to mistake other hyperechoic structures and artifacts as central venous lines, with some examples being heart valves, portal veins, peritoneal lining, sumps/feeding tubes, bone artifact, and air artifact. Additionally, once the line reaches the right atrium, it is a common mistake to assume that the tip of the catheter ends where it is seen. It is important to follow the entire length of the catheter through fanning, sliding, or rocking the probe to confirm the true tip location. However, once in the right atrium, the catheter often travels into a different plane, requiring a different window or probe position to be sufficiently interrogated by the ultrasonography beam. The ultrasonography user should assume a deep position once the line is seen entering the right atrium, even if the tip is not definitively visualized; ideally, this line should then be dynamically retracted under ultrasonography guidance until the tip is seen moving out of the right atrium. If there is a question of tip identification, the line can be flushed to visualize hyperechoic fluid bubbles emanating from the tip, allowing for definitive identification of the tip.10 Because of these possible missteps, providers new to this central line positional assessment with ultrasonography should always corroborate their study results with plain film radiographs as they develop their skills and gain experience.Central line positional assessment by ultrasonography is a powerful tool with growing evidence of superiority as compared to traditional assessment with radiography. However, it is a challenging skill that requires training to master. It can be learned by any member of the care team, including not only physicians and advanced practice providers but also by vascular access nurses.11 This tool allows for real-time line assessment to minimize costly and catastrophic complications of line complications that are not infrequent among even the most meticulous neonatology teams.