bubble study part one : correct technique in shunt from right atrium to left
atrium the blood fluid velocity is very low and cannot be detected by
color Doppler. for solving this problem we inject agitated saline through a peripheral
vein. agitated saline is a solution that consists of ninety percent
normal saline and ten percent air microbubbles. microbubbles are very tiny
their size are between 20 to 40 microns but they are very hyperecho and in
ultrasound we can see them very clear and obvious as you see on this image.
when we inject bubble through the vein in a few beats later they show up in
the right heart and if there is any shunt between right to left
those bubbles some of them or many of them come and show up in the left
side. when we do bubble study?
the most common indication for bubble studies is
rule out right-to-left shunt, like when we have paradoxical thromboembolism- is
the time that we have some trombosis forming in venous system and come to the
right heart and true shunt go to the left side and finally causes systemic
trumboembolism and patient for example get (vascular) attack, like TIA or stroke or in
any other equivalents forms- or we have hypoxemia and we cannot find the reason
and source for the hypoxemia. Another indication for bubble study is when we
are dealing with a critical patient and we need measure pulmonary
pressure but we don't have enough TR for catching on Doppler or we are not
sure is that underestimating or not? in those cases we can use bubble study for
increasing sensitivity of Doppler study. Another indication for bubble study or
agitated saline test is when we are suspicious to persistent superior
vena cava. in this venous anomaly usually we see prominent coronary sinus. in that
case we go and do bubble study.
for performing bubble study we need two
people; one Echo tech and another assistant. assistant is responsible for
preparing, getting IV line and injection solution that in most centers, usually is nurse.
but it can be physician assistant, physician or a trained echo tech.
equipments we need
10 milliliters syringes 4- 6; 3 way; angiocath; normal saline and bandaid.
Nowadays, in most centers the syringes are filled with nine milliliter normal
saline and ready to use. which vein we inject ?
we inject in
any major vein in right arm but if we have any restriction, for
example patient has AV fistula or doesn't have arm , because of amputation
or any reason, we can use left arm or even femoral vein. How we prepare agitated saline?
We mix 9 milliliter normal saline with one milliliter air and by
using three way and another empty syringe and pushing back and forth fast 10
to 20 times all air divided to the micro bubbles and disappear in
syringe and dissolve inside of the normal saline.
Meanwhile the assistant
is preparing and getting IV and all set up, we go and set up our machine. Since we
are recording as a clip we go and setup saving time for 10 to
15 seconds, but in with valsalva -that we do in next step, is
better we setup record time between 15 to 20 second and we record in
prospective manner, but if you are comfortable you can record as
retrospective and then we annotate. for example we put as bubble / rest.
Then we go and find a good four chamber view- it doesn't matter subcostal or apical- we go first
subcostal if we couldn't, we go apical. any of them that give us clear four
chamber especially with both atrium and interatrial septum clear and
obvious we used that window.
then we do bubble study in two steps: at rest and
with Valsalva. at rest just when you and patient are ready assistant
inject agitated normal saline 10 milliliter very fast through IV line, in
2 or 3 seconds and after a few beats we will see bubbles come show up through the
right atrium and then right ventricular. if there is any shunt bubbles will come to
the left side. more than 2 or 3 bubble in the left side is positive and we don't
need to go to do with Valsalva stage. otherwise we have to do bubble study
with valsalva.
in Valsava we exhale against closed glottis. it
is exactly the same way that we tight up belly or bear down during any activity
or defecation. so during Valsalva, strain phase we push or bear down the
intrathoracic pressure increased. when intrathoracic pressure increased the
blood return to the right side decrease but at the first few seconds at the same time
left-side pressure increases but total during five to ten seconds of strain that
patient keep pushing always pressure on the left side is higher than right side
but right after stop straining and patient start relaxing at the first
few beats- one or two second or three second the blood return to the right
side increases and meanwhile the blood return to the left side decreases. At those
first few beats- right after strain at the rest, pressure in right
atrium goes higher than left atrium and if we have any degree of shunt we can
detect it on image. before we start performing Valslava and recording first
we have to go practice one or two times with the patient and explain to him or
her that what is going on and how she or he should cooperate, and during that
exercise we find a good window for recording during strain and
after strain and make sure we're having good window. with those changes, our
image are in good quality.
when everybody is ready we first
hit the record and then tell the patient halfway breathe in and bear down or make
his or her belly tight- at the same time assistant injection
agitated saline through the IV line very fast , again in two or three a second and
we are watching monitor and right side and left side. As soon as the bubbles
show up in right atrium or five to seven seconds after starting
strain- whichever comes sooner- we tell the patient stop and relax. that first few
moments that patient stopped and relaxing start those moments are
critical and we have to try to catch it that time on our record. During that time
that we tell the patient stop pushing and start relaxing if assistant raise
the patient's arm up it can improve our quality of image.
if at the first attempt
we were not satisfy with our study for any reason, for example patient couldn't
do very well Valsalva or our view wasn't good we can try and repeat this
study one or two more times.