X-Message-Number: 33377
From:
Date: Mon, 28 Feb 2011 02:00:35 EST
Subject: Melody Maxim's Distorted Reality 12
Mike Darwin: ***Since I am opposed to using hard-shell open reservoirs I
wont comment here beyond saying that Boons interpretation is correct.***
4. Melody Maxim: Deleted excess connectors from AV loop.
Its best to have only the two cannulae connectors most likely to be used
inserted in the AV loop, with others available.
Mathew Sullivan: As mentioned during the meeting, I recommend that we
universalize our cannulae connections by inserting any appropriate fittings
deemed necessary to our cannulae and re-sterilize them. This ensures no matter
if we are working on a full sized adult or a small child that we can
connect the cannulae to the tubing without having to make any last minute
adjustments. The most obvious example of this might be to insert a x
connector
into a venous cannulae, then re-sterilize it. This may seem strange to
perfusionists out in the real world considering they would use a small tubing
circuit with the interest in a small circuit volume for a child, but our
tubing packs are one size fits all and this is okay in our situation because
we do not have the same concerns associated circuit volume and the need for
blood.
We should also consider or debate the possible use of quick disconnects
made by Qosina that Medtronic was using at Mechanisms.
Mathew Sullivan: Question is what are the percentages that you will be
working on a small child, my guess is probably not often. The quick
disconnects that Medtronics Resting Heart System circuits are using may be a
good
solution.
Mike Darwin: ***Unfortunately, I dont have the text at hand, but Alcor
recently (last 12 months or so) pumped a patient full of air in the field
because they did not have the right sized connector and the mortician tried to
jury-rig something which, as best I can tell, created a venturi at the
connection between the arterial line and the arterial cannula thus allowing for
sustained and undetected (until foam came out the venous line) air
embolization. In several cases perfusion was either not possible, or mortuary
cannula and/or equipment had to be used because there was a missing connector.
One of these cases was the mother of a world-renowned biomedical researcher.
I have been criticized for calling people who do this kind of things
IDIOTS, but I honestly dont know what else to say. The first time it happens is
inexcusable, but to have it go on, and on, over 15 years is sheer idiocy.
Nevertheless, this is the way it is. An inexperienced person digging through
lots of supplies on a tray or in a kit-box may be unable to find or
recognize the right sized coinnector. I know that seems impossible to you (and
me) but it has happened. I used to keep every conceivable sized connector in
my goat so that when I filled the goat with saline I would empty out my
pile of connectors onto the cutdown or major thoracic tray thus they were
always at hand and in the sterile field. And, of course, I could tell a x 3/8
connector from a 3/8 x 3/8 connector on sight. You only get that ability
by handling these things on a near daily basis.
While you may well know in advance that you are doing a child, and the
odds may be low, you cant count on that. No child has been cryopreserved since
the early mid to late 1970s. However, there are children signed up and
there may well be a pediatric at-need case. You need to at least be able to go
from 3/8 to .
What is more, I kept a selection of stainless steel cannula on my tray
(maximum size 6 mm OD) which I could use on very atherosclerotic patients. The
femorals of some elderly patients will only accommodate a small cannula and
these all have tubing barbs. You can easily deliver 5 LPM a minute
through such a cannula (I did it all the time on dogs) albeit at the price of a
high back-pressure between the pump and the cannula.***
Melody Maxim: The venous cannula currently being used has an incorporated
3/8 connector.
Mathew Sullivan: I dont know that we have come to any firm conclusion on
which cannulae we will be using, but if or when this becomes the standard,
the tubing should not go past the first barb to make for easy removal of the
tubing. Speaking thereof, the AV loop on the training pack has both of its
cannulae connections past both barbs and if this were done on a real tubing
pack, expect the surgeon to complain a lot. Tubing or connectors meant to
be removed to make way for cannulae connections should not go past the
first barb to make for easy removal.
Melody Maxim: The arterial cannula does require a 3/8 connector, so one
with a luer lock has been included.
Melody Maxim: Discuss whether this luer lock is acceptable to replace the
previous manometer port connector.
Mathew Sullivan: My assumption here is that we will be going with the
arterial cannulae with pressure manometers built within unless someone can
think of a reason not to; therefore, the 3/8 LL connector will need a one-way
stopcock to allow for the removal of large amounts of air, sampling for those
who will insist on taking a sample there, or even for those who might want
to use a florescent die to look at patient circulation as an example as
has happened in the past. We used to have this type of connection next to the
cannulae at Alcor, but the surgeons complained enough that we moved it
back a few inches to allow for better handling and making the cannulae
connection.
Boon: I think the purpose of having a luer lock on the 3/8 connector for
the arterial cannula is to allow air (if any) to purge out when connecting
to the arterial line from the pump. I do not agree with putting a one-way or
a 3-way stopcock there to allow for taking an arterial blood sample or for
measuring the arterial line pressures. You dont want to mess around with
the arterial cannula once it is in place. Instead put a 3-way stopcock on top
of your arterial line filter to have access for blood sampling and
checking your arterial line pressures is a better way to go.
Mike Darwin: ***This has been an endless source of frustration for me. No
one has listened to me over this issue for the last 15 years so I hardly
expect them to start now. (Forgive my cynicism.)
Pressure cannot accurately be measured in back of the arterial cannula at
all but the lowest flows with the largest diameter cannulae. In order to
measure pressure via the arterial cannula it is necessary to pass an
intracath beyond the tip of the cannula and then hook this up to a pressure
transducer. Yes, it can be a manometer, but this is pretty pathetic and very
dangerous. Solid-state disposable pressure transducers and portable, compact,
battery powered (NiMH no less!) monitors are now available. USE THEM! Use them
not only to monitor MAP but to monitor CVP or even venous line pressure at
the venous cannula, if nothing else is available.
What you are measuring when you measure pressure behind the arterial
cannula is the back pressure generated by the constriction of flow represented
by the arterial cannula. The long fluid filled line leading to the manometer
is just air embolism machine waiting to spring into action.
The idea of the 3/8th connector near or on the arterial cannula being used
to work air out of the system before going on bypass is not understandable
to any professional cryonicists now engaged in perfusing people (that I
know of). They assume that if you dribble fluid out of the arterial cannula
when you insert it into the arteriotomy that you MUST therefore have no air.
It is impossible to convence them that AFTER the arterial cannula is placed
and secured that you must draw back blood and work out any bubbles. If
they dont see any air in the line when the insert the dripping cannula into
the artery, they dont believe there can be any. The fact that air may have
entered the artery via the arteriotomy and be present between the arteriotomy
and the proximal arterial ligature appears to be an impossible concept for
them to wrap their minds around. Of course, in the real world, if you fail
to do this you will pump air and you will usually have a detectable
neurological deficit to contend with.
Similarly, if you simply do the rote exercise of aspirating the vessel
after the proximal tie is released you will almost always SEE air. However, if
you always refuse to do this you will never see the air and therefore you
will never remove it. And, since your patient never wakes up, you never see
any harm in this Indeed, after you have completely filled a patient up
with air and blown him up like a balloon you can confidently state: Despite the
problems during surgery, the cryoprotection went fairly well.
So, yes, you need a 3/8 connector with 4-way stopcock at the arterial
cannula to remove air prior to going on bypass.***
5. Melody Maxim: Removed a 3/8-1/4 reducer, as well as a tube inside a
tube connection, from the AV loop recirc line and changed the tubing from 1/4"
to 3/8.
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