Dialysis catheter tip position on POCUS: may not be straightforward
Before using a newly inserted central venous catheter or dialysis catheter, we generally obtain a chest radiograph. However, in acute care settings, we can employ a rapid atrial swirl sign (RASS) as an immediate indicator of catheter usability, eliminating the need for an X-ray in most cases. This technique involves injecting 10 cc of normal saline (preferably agitated saline, but not necessarily) into the catheter and observing the right atrium (typically in apical or subxiphoid 4-chamber cardiac views) for the presence of bubbles. If a noticeable fluid swirl or opacification occurs in the right atrium within 2 seconds of the saline flush, it indicates optimal subclavian and internal jugular central venous catheter placement. This finding confirms that the injected fluid is reaching the intended location within intended time frame. The images below illustrate this sign. In addition, POCUS allows us to assess pleural sliding and exclude clinically significant pneumothorax. It would be helpful to sono-auscultate relevant lung zones before and after the catheter placement.
On the other hand, solely relying on POCUS to accurately determine the position of the catheter tip (if at all you need to) can be challenging. Although the subxiphoid snail view seems promising for locating the catheter, it is not always easy to obtain this view. Even when a good view is obtained, tracing the entire length of the catheter, and visualizing its tip can be difficult. Here is an illustrative example that demonstrates the presumed catheter tip at multiple levels depending on the angle of insonation. The correct position, slightly into the inferior vena cava, is depicted in Figure 4, along with the corresponding chest X-ray. The patient exhibited satisfactory blood flow during dialysis, without any observed arrhythmias, and the line was left in place without retraction.