POCUS for Catheter Placement: Relevance to Nephrology

Tejas P. Desai, MD


September 14, 2018

Quick Glance at the Past and Future of Nephrology

The field of nephrology has certainly had its share of "ups and downs"; the mid-half of the 20th century was perhaps the period of most advancement. Dialysis machines were developed and offered to an increasing number of patients, and were modified to become the safe and reliable procedure that we know today. Transplantation was also reaching new heights, with an increasing number of successful transplants performed and improved mortalities post-transplantation. Indeed, in the United States, the mid-20th century saw one of the greatest public policy wins that nephrology, and quite possibly any medical specialty, has ever had, with the universal coverage of dialysis patients under the Social Security amendments.

Given those victories, it may not be such a surprise that victories in nephrology began to slow down. The latter half of the 20th century and the first decade of the 21st century saw a decline in randomized trials and an overreliance on database studies. Fellowship positions increased, but applications started to fall. Procedures that were once exclusively within the purview of nephrologists (eg, peritoneal dialysis catheter placement, initiation of continuous renal replacement therapies) were steadily being performed by providers with limited to no nephrology experience.

Some readers might believe that we are still in that period, but I contend that the past 4 to 5 years have shown a reversal in the fortunes of our field. Randomized trials are returning to nephrology (with some trials, like TEMPO 3:4[1] and CREDENCE,[2] offering us positive results) and the number of fellowship applicants appears to have stabilized. Young nephrology educators have contributed to the field's revival by introducing new educational tools (eg, infographics, visual abstracts, gamification, case-based and distance learning) and new procedures. The most notable of the latter is POCUS: point-of-care ultrasonography.

Source: Alamy

Ultrasonography has a number of uses currently being explored.[3,4] Beyond the traditional uses such as kidney measurements, echogenicity, and structural derangements, bedside/chairside ultrasonography has been used to assess volume status in dialysis patients, fistula health, and in a recent PLoS One study, central venous catheter tip placement.[5]

Ultrasound-based Catheter Placement

Researchers in Germany evaluated and calculated the test characteristics of bedside ultrasonography to correctly identify catheter tip placement in patients receiving an internal jugular vein catheter.[5] In this prospective study, infusion of saline through the catheter and identifying the subsequent saline swirl (referred to as the rapid atrial swirl sign, or RASS) was compared against the standard chest roentgenogram (CXR) in 100 adult patients both mechanically ventilated and nonventilated.

The primary outcome was the performance of detecting correct and incorrect catheter placement using the bedside ultrasound when performed by both attending and trainee physicians. A positive RASS was defined as seeing an immediate opacity in the right atrium after saline infusion (+ swirl sign) and indicated proper catheter tip location, while a negative RASS (either no opacity in the right atrium or a delayed visualization of the opacity) indicated catheter malposition. An interesting secondary endpoint was based on the ultrasound operator's level of experience: attending physician versus resident trainee.

Of the 83 patients whose ultrasound revealed an immediately positive atrial swirl sign (+RASS), all 83 received a CXR that confirmed correct catheter placement. Of the 17 patients whose ultrasound suggested a malpositioned catheter (ie, a negative RASS), the CXR confirmed malposition in 12 and overturned the ultrasound in five cases. These numbers resulted in the following test characteristics: sensitivity 100% (95% confidence interval [CI], 69-100), specificity 95% (95% CI, 88-99), positive predictive value of 71% (95% CI, 49-87), and a negative predictive value of 100% (CIs not provided by the authors). In the subgroup analysis, the ultrasound operator's training level (attending versus trainees with 1 to 6 postgraduate years) did not impact the aforementioned four test characteristics in a significant way.

Ultrasonography Use in Nephrology: Thoughts?

POCUS is proving itself to have broad relevance for nephrologists. In this particular study, untrained ultrasound operators were successfully able to identify catheter placement in a central vein. The positive findings add further plausibility to using a bedside ultrasound for nondialysis catheter insertion and placement confirmation. Along with impressive test characteristics, detection of the saline swirl using the ultrasound would save time in catheter confirmation and limit patient/provider radiation exposure.

Additionally important are the secondary findings that suggest a low barrier-of-entry in using the rapid atrial swirl sign. Indeed, I was excited about the prospects of this test, but was disappointed with the results of a recent Twitter poll in which an overwhelming majority of nephrology providers still favored the CXR (see figure).

Figure. Ultrasonography poll.

So tell us what you think. Are the findings of this study (or others of which you are aware) impressive enough for you to consider ultrasound-based catheter confirmation?

Follow Tejas P. Desai, MD, on Twitter: @nephondemand

Follow Medscape Nephrology on Twitter for more nephrology news: @MedscapeKidney


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