Surgery
FlowSound® Audiovisual Volume Flow Analysis
Bypass Graft Patency Related to Vocal Pitches
Normal Vocal Range
The Transonic® Flowmeter measures absolute
volume flow – and Transonic’s proprietary
FlowSound® communicates these values
audibly, so that a musically attuned surgeon
comfortable with FlowSound® can save
precious minutes in confirming functionality
without taking the eyes from the surgical
field. Even more time can be saved when
examining grafts with technical error.
G3
1.5; 2 mm <0.9
High C
Hum
FlowSound® is a powerful tool in the arsenal
of a CABG surgeon experienced in “FAST” –
Flow-Assisted Surgical Technique.
Middle C
Introduction
C4
E4
G4
C5
E5
G5
C6
F6
C7
1.5
2.5
3.5
6
10
15
25
50
100
3 mm
<1.8
3
5
7
12
20
30
50
100
200
4 mm
<3.5
6
10
14
25
40
60
100
200
400
Probe
Flow in mL/min
Transonic Flowprobes’ Flow - to - Pitch (FlowSound) Conversion
®
Probe Size
Acceptable FlowSound ® Flow Ranges
1.5; 2 mm
Volume Flow
≥ C6 (an octave above high C)
≥ 25 mL/min
3 mm
≥ E5 (E above high C)
≥ 20 mL/min
4 mm
≥ C5 (High C)
≥ 25 mL/min
Unlike Doppler’s“swoosh-swoosh” flow
Fig. 1: FlowSound pitch-to-flow conversion for CABG 1.5 mm - 4 mm. Flowprobes.
velocity sounds, the calibrated pitches of
Comparing FlowSound pitches between systole and diastole provides
FlowSound® provide direct audio feedback of
feedback on the systolic/diastolic flow ratio and graft patency. Sounds within
bypass graft VOLUME FLOW!
the normal vocal range are generally too low for a patent CABG graft.
FlowSound CABG Flow-Assisted Surgical Technique (FAST)
Measurement Preparation
• Apply sterile gel inside the Flowprobe. Turn on
FlowSound. A steady hum (Fig. 1: piano keyboard
low G3) will be heard. The hum is the sound
pitch for any flow near zero and below the
Flowmeter’s minimal zero offset.
• When a Flowprobe is applied to a graft,
FlowSound “plays” the graft’s pulsatile flow
(see Fig. 1 & sidebar below). When the
Flowprobe is held steady, a repetitive beatby-beat FlowSound is generated.
• The Flowprobe measures any motion within its
flow window. Therefore, if the probe is moved,
a “motion artifact” will generate a FlowSound
spike that distorts the Pulsatility Index (PI). If
FlowSound® is jittery, it could indicate turbulence
caused by too large a vessel stuffed into the
Flowprobe’s window.
FlowSound Pitch
An increase in FlowSound’s
Do Re Mi Fa So La Ti Do
pitch by one-half tone (E to F
C D E F G A B C
[Mi to Fa]) corresponds to a
12.5% increase in volume flow. One full tone increase
in pitch (F to G [Fa to So]) corresponds to a 25%
volume flow increase. An octave (C to C [Do to Do])
change in pitch equates to a four-fold volume flow
increase.
FlowSoundAdvantage(CV-23-tn)RevA2014USltr
Audiovisual Graft Patency Assessment•
Listen to FlowSound and observe the heart beating.
1.Temporarily Eliminate Competitive Flow
Competitive flow from the native coronary
artery reduces and sometimes reverses graft
flow. One should, therefore, measure the graft
at its maximum flow capacity. Temporarily apply
finger pressure to the native vessel proximal to
the anastomosis. If competitive flow had been
present, the FlowSound pitch will increase,
indicating its elimination.
2. Diastolic Dominant Left Heart FlowSounds
Contracted muscle resists inflow. Therefore, on
a good graft to the left heart, one would expect
low flow (a pitch within one’s vocal range) during
systole, and a far higher pitched FlowSound
(above one’s vocal range) during diastole for a
“Diastolic-dominant Flow Profile.”
3. Systolic/Diastolic Balanced Right Heart
FlowSounds
The right side of the heart contracts less
forcefully than the left heart. Therefore,
bypass graft flow to a right heart coronary is
less impeded during systole. Both systolic and
diastolic FlowSounds to a good right heart graft
will be above one’s vocal range.
Surgery
FlowSound® Audiovisual Volume Flow Analysis cont.
Technical Error Troubleshooting Using
FlowSound
If an audiovisual inspection of graft patency indicates
the need to examine the graft for technical error,
FlowSound® provides instantaneous feedback on
whether manipulation of the graft will affect flow.
Again, be sure to rule out competitive flow first.
Fig. 2.: Competitive flow is evident from the negative flow spike on the right
side of the waveform caused by reversal of flow through the graft at
the start of systole. Competitive flow spikes increase the PI reading,
and should be eliminated for a valid graft patency test.
Flow Reversal = Negative Waveform Spikes
Since a native coronary artery connects to the base
of the aorta, the systolic pressure wave arrives at the
anastomotic site first via the native coronary circuit, before
it travels the longer bypass graft route. In the presence of
competitive flow from the native coronary, this reverses
flow through the bypass graft and creates a short peak of
retrograde (negative) flow on the flow waveform at the
beginning of systole.
Flowsound Graft Patency Assessment
1.If mean graft flow is above 25 mL/min (above
20 mL/min for a smaller patient), graft flow is
good. FlowSound’s pitch will be well above the
normal vocal range. Mean flow is displayed on
the AureFlo® display and front panel LED of the
Flowmeter.
2.When mean flow is suspect (<20 mL/min),
technical error such as a misapplied stitch,
thrombus formation and distal obstruction in
the native coronary must be ruled out before
one can conclude that the poor flow results from
acceptable causes such as low blood pressure,
diseased cardiac muscle or a limited flow delivery
capacity of an arterial graft.
• If the graft is partially constricted from a misapplied
stitch at its distal anastomosis, the constriction
often limits graft flow. Central pressure governs
the graft’s flow profile more than systole/diastole.
Because central pressure is highest during systole,
you will hear some blood flow squeezing past the
constriction during a portion of systole, producing a
“systolic-dominant flow profile” where systolic pitch
is higher than diastolic pitch.
• With the Flowprobe applied to the graft, manipulate
the distal anastomotic site (tugging on anastomosis
may open up a constriction). A significant change
in FlowSound as the result of minor repositioning
of the graft indicates that there is a trouble spot on
this site.
• A fully thrombosed graft will exhibit no flow
pulsatility at all. FlowSound will hum its G3 pitch.
• In the case of sequential grafts, the distribution
between its branches is determined by the flow
resistance beyond their myocardial target sites. Test
each target graft at its full flow capacity individually
by temporarily constricting the other branches.
Transonic Systems Inc. is a global manufacturer of innovative biomedical measurement
equipment. Founded in 1983, Transonic sells “gold standard” transit-time ultrasound
flowmeters and monitors for surgical, hemodialysis, pediatric critical care, perfusion,
interventional radiology and research applications. In addition, Transonic provides
pressure and pressure volume systems, laser Doppler flowmeters and telemetry systems.
www.transonic.com
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