Improvised hastily by a young physician to avoid the embarrassment from direct auscultation of a particularly buxom patient’s chest, the stethoscope recently celebrated its 200th anniversary. After initial resistance, it has since become standard of care and a ubiquitous icon of the physician (1).
Technology has improved since the Napoleonic era, and more sophisticated devices are now available to augment the physical exam. Ultrasound was originally applied as sonar to hunt submarines in the First World War, but was quickly co-opted into the medical field. Early machines occupied entire rooms, but now powerful imaging devices are handheld and can be paired wirelessly with smartphones allowing ultrasound to be used on bedside rounds (2).
Point-of-care ultrasound (POCUS) has been used by obstetricians, cardiologists, and emergency medicine physicians for more than 20 years to answer focused questions and expedite clinical decision-making. In this time, POCUS has become increasingly incorporated into medical school curricula across the country. Some schools even provide point-of-care devices for all of their medical students; an entire generation of young physicians is training with concept of the ultrasound-stethoscope (2, 3).
Nephrologists have not fallen behind in this trend. Many already use ultrasound for dialysis catheter placement and percutaneous kidney biopsy. Interventional nephrologists are using ultrasound to look at fistula stenoses and renal intensivists have taken it a step further, bringing a suite of simple ultrasound tests to the bedside to diagnose undifferentiated shock.
Nephrology fellows are already demanding formal training in ultrasound. It was true in 2008 (4) and confirmed in a recent survey of fellows conducted in 2016. Whereas only 12% of fellows reported having formal ultrasound training, 44% wanted additional instruction in ultrasound interpretation (5).
Some uses of POCUS have intuitive value. For instance, immediate detection of hydroureteronephrosis or a distended bladder in a new consult with acute kidney injury can rapidly change management and has the potential to improve outcomes.
Other uses of POCUS are of less obvious value. The volume exam is one of these. While no physical exam finding is entirely sensitive or specific for volume depletion or volume overload, and even central venous pressure has fallen out of favor as a marker for volume responsiveness, ultrasound for determining volume status is still in its nascency. Inferior vena cava (IVC) collapse as a marker of volume responsiveness is interesting, but it is of uncertain value as a marker of volume overload in dialysis patients (6).
One bright spot is lung ultrasound for quantification of extravascular lung water (EVLW) in patients with end stage renal disease (ESRD) on hemodialysis (HD). Fluid overload in these patients is a well-known yet underdiagnosed independent risk factor for adverse cardiovascular outcomes and death (7).
When applied to the lung, ultrasound was initially thought to be valueless as reverberation artifacts termed “A-lines”—viewed as serial horizontal reflections of the pleural line—obscured anatomic visualization of the lung parenchyma (Figure 1). It was soon realized that as alveoli fill with fluid and the alveolar interstitium thickens, this A-line pattern gives way to another pattern of hyperechoic lines, termed “B-lines,” which radiate perpendicular to the pleural line (Figure 2).
Lung ultrasound obtained using a curvilinear wireless ultrasound device paired with a smart phone. A-line pattern. Note the serial echogenic lines evenly spaced running parallel to the pleural line. This image depicts normal healthy lung obtained from the author.
Photo Credit: Nathaniel Reisinger, MD
Citation: Kidney News 9, 7
Lung ultrasound obtained using a curvilinear wireless ultrasound device paired with a smart phone. B-line pattern. Note the echogenic lines emanating from the pleural line and running deep to the edge of the image. This image is obtained from a young woman who presented with dyspnea and was found to have pulmonary edema due to volume overload related to advanced lupus nephritis. Following dialysis and ultrafiltration, the B-line pattern reverted to an A-line pattern. Reproduced with patient’s permission.
Photo Credit: Nathaniel Reisinger, MD
Citation: Kidney News 9, 7
The converse is also true, B-lines disappear dynamically during dialysis correlating with ultrafiltration volume (8). A total B-line score can be measured serially over 4, 8, or 28 intercostal spaces and this score correlates with EVLW as measured by thermodilution (9).
What’s more, B-line score diagnoses subclinical pulmonary congestion more often than physical exam (10). As expected, B-line score correlates with cardiovascular outcomes, death, and even readmissions, the bane of fellows everywhere (11). A multi-center, prospective, randomized clinical trial (LUST trial) is ongoing in Europe using a B-line score directed ultrafiltration algorithm to mitigate fluid overload in patients on HD. This trial uses a well-validated web-based tutorial to ensure interobserver agreement among nephrology and cardiology attendings (12).
The first question I’m asked by attendings is how to bill for this. It’s possible to bill for a limited ultrasound and for some a bedside ultrasound can add to critical care time to enhance relative value unit generation. Where I see lung ultrasound being most valuable is on the population level.
The LUST trial is powered to detect a 33% reduction in cardiovascular events. Such a powerful and cost-effective technique to improve patient outcomes is sure to garner attention from large dialysis organizations (LDOs). LDOs have the economies of scale needed to implement the technique broadly. As our health system moves from fee-for-service payments toward performance-based metrics, LDOs stand to realize shared savings through ESRD Seamless Care Organizations (ESCOs) if they can demonstrate strategies to reduce cost to Medicare.
For the individual, the benefit of POCUS is clear: to answer focused clinical questions to enhance the physical exam. Basic competency in POCUS will become a necessary skill for practicing nephrologists as trainees from medical students to fellows start to demand training.
References
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