TECHNICAL NOTE
Ultrasound Detection of Microembolic Signals
in Hemodialysis Accesses
David Woltmann, DO, Richard A. Fatica, MD, Jonathan M. Rubin, MD, and William Weitzel, MD
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Microembolic signals (MES) detected by ultrasound, thought to be of gaseous or solid origin, have been
described with decompression illness and in the intracranial and cardiopulmonary circulation. We describe the first
reported cases of MES occurring in hemodialysis accesses. Two hemodialysis patients, one with a synthetic graft
and one with an arteriovenous fistula, showed MES during a dialysis session detected by duplex ultrasound. We
postulate that these MES represent cavitation bubbles developing from turbulent blood flow around the venous
needle in the access. However, other potential causes exist, including air introduced into the circulation from the
dialysis circuit or microemboli arising from thrombus or atheroma.
2000 by the National Kidney Foundation, Inc.
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INDEX WORDS: Hemodialysis; microembolic signals (MES); arteriovenous (AV) fistula; arteriovenous (AV) graft;
duplex ultrasound.
LTRASONOGRAPHY has been used for
the diagnosis of microembolic signals
MES) in the cardiopulmonary circulation, intra-
graft. No MES were recorded at lower pump speeds. The
portion of the graft proximal to the venous needle was not
examined.
U
(
cranial circulation, and in association with decom-
pression sickness.1 We report the first known
cases of the ultrasound finding of microembolic
signals in a dialysis access graft during dialysis.
Case 2
-7
A 79-year-old man with ESRD from thrombotic microan-
giopathy was receiving dialysis through a left arm arteriove-
nous (AV) fistula. Volume flow, as measured by duplex
ultrasound (ATL HDI 3000 Ultrasound, 6.0 MHz ATL
CL10-5 linear array transducer), was 728 mL/min. At a
dialysis blood pump speed of 400 mL/min, MES were seen
downstream from the venous needle returning to the central
circulation. No MES were seen between the arterial and
venous needles. Figure 2 shows his Doppler wave form with
a bright Doppler signal where an MES appears.
CASE REPORTS
Case 1
A65-year-old woman with end-stage renal disease (ESRD)
from type 2 diabetes mellitus was receiving chronic hemodi-
alysis through a left forearm synthetic polytetrafluoroethyl-
ene dialysis access graft. The patient had severely compro-
mised blood flow through her graft, resulting from a venous
anastomosis stenosis previously demonstrated by angiogra-
DISCUSSION
8
Ultrasound has been used to detect venous air
bubbles as MES in decompression sickness,6 as
well as from inadvertent air embolism during
phy. This resulted in access recirculation measured as high
,7
as 40% at a dialysis blood pump rate of 400 mL/min. Duplex
ultrasonography (ATL HDI 3000 Ultrasound; 6.0 MHz ATL
CL10-5 linear array transducer, Bothell, WA) was used to
measure the volume flow though her graft (172 mL/min) and
to examine the retrograde blood flow in her graft between
the dialysis needles during dialysis as part of a separate
1
vein catheterization. Several authors have de-
scribed the ultrasound finding of MES in the
intracardiac circulation in patients with mechani-
cal heart valves and have postulated that turbu-
9
,10
study. MES such as that shown in Fig 1 were seen in the
bloodstream within the graft at a dialysis blood pump setting
of 400 mL/min, corresponding to the greatest degree of
reversed flow (from venous to arterial needle) through her
lence from acceleration and deceleration of blood
2,4,5
caused cavitation bubbles.
Perhaps cavitation
bubbles formed in patient 1 as a result of needle
orientation with retrograde flow at higher dialy-
sis pump rates. It is also conceivable that decom-
pression bubbles formed in the access from the
higher venous pressures generated within the
blood line at higher dialysis blood pump rates. In
patient 2, MES could conceivably have been
formed from flow through his tortuous fistula;
however, no MES were seen upstream from the
venous needle. Because in both patients MES
were seen downstream from the venous needle,
From the Departments of Internal Medicine and Radiol-
ogy; Division of Nephrology, University of Michigan, Ann
Arbor, MI.
Received March 31, 1999; accepted in revised form Octo-
ber 8, 1999.
Address reprint requests to William Weitzel, MD, Univer-
sity of Michigan Medical Center, 3914 Taubman Center, Ann
Arbor, MI 48109. E-mail: weitzel@umich.edu
2
000 by the National Kidney Foundation, Inc.
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0
272-6386/00/3503-0020$3.00/0
526
American Journal of Kidney Diseases, Vol 35, No 3 (March), 2000: pp 526-528
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