Point of care ultrasound: A new tool for the 21st
century nephrologist
Abstract
There is an exciting change happening in nephrology training.
Across the country, nephrology programs are bringing point of care ultrasound
into their curricula. Nephrologists and nephrology trainees are not only using
point of care ultrasound for the assessment of kidneys and bladder but also for
volume assessment. In this article, we describe how our nephrology division
designed a hands-on point of care ultrasound course for nephrology fellows. We also
describe some important anecdotes from our experience that highlight the
utility of this novel tool.
A new
assessment tool for nephrologists
Across the country, nephrology fellows are being taught to use
ultrasound at the point of care to make timely decisions about their patients.1 ,2 The
movement to incorporate ultrasound training into nephrology dates back about a
decade. In 2008, a survey of nephrology program directors found that some
programs already offered training in diagnostic renal ultrasound and that 13%
of programs planned to formally incorporate performance and interpretation of
ultrasound into their curricula within a year.3 In
a follow up survey in 2014, we found that most programs still did not have
ultrasound training but that some programs offered two- or four-week rotations.4
Neither survey differentiated between ultrasound performed as a
formal study and those performed at the bedside. In the last few years,
ultrasound machines have become more portable and more affordable. Availability
is increased as many emergency departments and ICUs house their own ultrasound
machines. Therefore, opportunity exists for nephrologists to use ultrasound at
the point of care to determine kidney size, measure bladder volume, assess for
hydronephrosis, and even to evaluate volume status. Thus, the future of
ultrasound training in nephrology may be in teaching-focused exams to answer
discrete clinical questions rather than teaching complete examinations of the
retroperitoneum and bladder.
At our institution, we are privileged to have international
experts in point of care ultrasound in our critical care faculty. They have
been instrumental in popularizing and promoting a whole-body approach to point
of care ultrasound (POCUS). Each year they give several three-day courses for
the American College of Chest Physicians as well as a course for incoming
pulmonary and critical care fellows. They have done a substantial amount of
educational research and have refined their technique over time.5 In
the last decade, this teaching faculty at Hofstra-Northwell School of Medicine
have instructed more than 15,000 trainees and have organized a focused course
for our nephrology division.6
A significant portion of the course focused on using lung
ultrasound to assess volume status. Lung ultrasound has the potential to be a
revolutionary, paradigm-shifting tool for leading-edge nephrologists (see
sidebar).
How a
lung ultrasound can help measure volume
Over the last two decades, intensivist Daniel Lichtenstein has
demonstrated that when an ultrasound beam hits the surface of a normal lung, it
generates artifacts called an “A line.” When an ultrasound beam hits a lung
filled with water, it generates a reverberation artifact that juts away like a
bright white rocket. These lung rockets are called “B lines.”7
A lines and B lines are shown in Figure 1. Research has shown that B Lines
correlate with gold standards of volume assessment.
Figure 1. A lines (left
image) are horizontal artifacts that appear parallel to the pleural line and
indicate a normally aerated lung. B lines (right image) are reverberation
artifacts generated by water-thickened interlobular septa and represent pulmonary
edema in the appropriate clinic setting.
For nephrologists who are unfamiliar with lung ultrasound, there
are three “need to know” points. First, B lines are a reliable method for
determining volume status in dialysis patients. Second, a higher number of B
lines in these patients correlates with greater mortality. Third, lung
ultrasound is teachable and takes less than ten minutes to perform.
Since our initial training course in 2015 and subsequent
refresher course in 2016, our division has started to incorporate point of care
ultrasound into clinical practice. In one illustrative example, we were faced
with an elderly woman with chronic kidney disease who was admitted with an
acute exacerbation of congestive heart failure. In the setting of diuresis, the
patient’s creatinine rose and she developed acute kidney injury. Her volume
status became difficult to discern by traditional physical examination and we
were concerned that we had gone too far with the diuretics. Emboldened by our
newly acquired skills, we performed a lung ultrasound. We found that the
patient had a diffuse B line pattern consistent with pulmonary edema––not seen
on chest x ray or appreciated on lung auscultation. Diuretics were increased
and the patient’s creatinine improved back to baseline as her heart failure
resolved.
In another example, we used focused renal ultrasound to assess
an elevated creatinine in a patient being considered for a left ventricular
assist device (LVAD). In these patients, it is of paramount importance to
identify whether the patient’s kidneys are intrinsically normal. At the time we
evaluated this patient we did a point of care ultrasound examination. The
kidneys were normal in size and had normal cortical thickness, there was no
hydronephrosis, and the patient’s bladder was collapsed around the indwelling
urethral catheter. This timely information, in conjunction with a bland urine
sediment and a low urine sodium, enabled us to confidently identify the
patient’s heart failure as the cause of his kidney injury. Ultimately the
patient’s creatinine returned to normal two days after LVAD placement.
The value of being able to rapidly discover urinary obstruction
is immeasurable. A patient presented to our outpatient clinic for evaluation of
an elevated creatinine. Based upon history, obstruction was suspected. A quick
look at the patient’s bladder post void proved the case. The patient was
referred to a same day urology appointment where an indwelling urethral
catheter was placed. In this case, hospitalization was averted and a brewing
renal injury was recognized early.
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