X-Message-Number: 33378
From:
Date: Mon, 28 Feb 2011 02:41:15 EST
Subject: Melody Maxim's Distorted Reality 13
Content-Language: en
Mathew Sullivan: I'm not sure about the 3/8 x A connector, since the new
tubing packs under construction do not have this item in the AV loop.
Melody Maxim: Increasing the tubing size eliminates the need for the two
extra connectors, (especially the extremely undesirable tube inside a tube
connection),
Boon: Because I have not seen the circuit, I don't know what she means by
tube inside a tube connection. However, I have to agree with her on
eliminating any unnecessary extra connectors, if you can.
Mathew Sullivan: There may have been a legacy item leftover in the
training pack in regards to the tube inside a tube, but if you look at the other
tubing packs on the table you won't find any solvent bonded connections. I
know some people have expressed concern about solvent bonded connections
(calling it a glued connection which it is not) sighting they have never seen
it before, but I have purchased tubing circuit products that had tubing
bonded to products and you have also mentioned the use of bonded products, so
I'
m a bit confused when I hear statements such as extremely undesirable. The
only thing that I wonder about is some form of unwanted reaction as a
consequence of using the solvent, but I possess no knowledge to make such an
assertion and can only speculate as to why some here are objecting to it. I
expressed concern about this while working at Alcor, but I was told that it
was a solvent and not a glue, so there wasn't anything to be concerned
about. If I remember correctly, I was informed that the solvent evaporates
away.
Mike Darwin: ***Solvent bonds are achieved by solventing (dissolving) the
two tubing segments into each other using cyclohexane. As Mathew notes,
they are widely used by manufacturers and often used to join large PVC and
acrylic components together. After EO sterilization and out-gassing there is
virtually no cyclohexane residue in the circuit. Cyclohexane joints must
never be used in the field only before sterilization and out-gassing.
Solvent bonds are undesirable only in that if they are facing the
direction of flow they tend to create turbulence which damages formed blood
elements. Connectors do this too, but usually to a much smaller extent because
they are designed to minimize turbulence and do not have the un-tapered surface
of the solvent joint.
Aside from the irreversibility of the joint, they are of no special
consequence. Done properly, I have never seen one fail and they are not
difficult
to do well. By contrast, I've seen plenty of tubing come off connectors,
albeit not on tubing packs assembled by medical manufacturers. The reason
in-house tubing connections may blow-off is due to the effects of
sterilization on the tubing and the connector. Heating of the tubing pack during
EO
sterilization and out-gassing (heated aeration) can cause tubing to relax and
connectors to shrink slightly. Manufactured tubing packs get around this
problem by electronically welding the tubing to the connector for all but
those joints that need to be broken to go on bypass.
My comments here are educational; I have no strong feelings one way or
another. I used solvent bonds mostly when I had a tight space or otherwise
wanted to avoid kinking from a connector. Solvent joins are much less likely to
kink on tightly coiled tubing, or on short-lengths of tubing such as the
recirculating connector line near the end of the AV loop (a feature common
to all ultraprofound hypothermic asanguineous perfusion circuits).***
Melody Maxim: and provides for recirculating at a higher flow rate.
Mathew Sullivan: Higher flow rates through the bypass are not necessary.
All that we need is a reasonable flow rate to maintain the temperature while
on bypass.
Mike Darwin ***Mathew is correct. The purpose of the bypass loop near the
end of the AV loop is to prevent warming of the perfusate (or blood) and
consequent out-gassing and bubble formation during any pause in bypass. If
you leave perfusate that has been cooled to near 0 degrees C in a line to warm
up it will fizz and form bubbles as the gas solubility of the perfusate
decreases with warming. This is true of the entire circuit and is why it is
critical to maintain flow so that bubbles will be swept into the filter and
so that the circuit and perfusate temperature can be maintained at a
constant and low temperature to avoid out-gassing in the first place.***
Melody Maxim: The tubing length seems adequate for positioning the tubes
in any desirable position.
Mathew Sullivan: We used to use the 3/8, but after sufficient complaining
on the part of the surgeons we switched to a 1/4, since it offers a greater
amount of flexibility, is less inclined to resist adjustment, and offers a
lower probability of having a permanent kink as a result of packaging and
sterilization.
The Keck clamp has also been replaced which means we will have to put the
old screw clamp back on in addition to the clamp that is on there now. This
means subtle adjustments in bypass can no longer be done with a single hand
easily with any degree of precision in the event the surgeon what it
during their procedures, to training events were we have demonstrated
backpressure.
Boon: If your arterial line is 3/8 and venous line is also 3/8, why would
you want your AV loop shunt line to be A ? I would use 3/8 for my shunt.
Mike Darwin: ***If you use 3/8 tubing for the bypass line you will find it
stiff and difficult to position. It is also much more difficult to occlude
completely, especially when cold. The use of A tubing is a lesson
hard-learned and should not be reversed.
Restore the Keck clamp! Screw type (Hoffmann compressor) clamps are
completely unsuitable for use anywhere in a CPB circuit. They are especially
dangerous with cold PVC tubing (remember the shuttle Challengers O-rings?)
because they do not reliably occlude in the cold and if applied when the tubing
is warm they may allow flow when it cools.
In addition to the Keck Clamp, I always applied a metal occluder to the
line; I don't trust plastic clamps of any kind for bypass, or even dialysis; I
've seen several (living) human patients killed by those damn things.***
6. Melody Maxim: Shortened tubing to perfusate bags and waste bags.
Having all clamps within reach is a safety feature, as it allows the
person operating the perfusion circuit to stay in close proximity to the
reservoir and pump. (Shortened lengths should still be adequate to position
perfusate and waste bags in a variety of position in the event of cramped
quarters.)
Mathew Sullivan: I agree and this helps to bring us in better alignment
with Alcor's tubing pack.
Mike Darwin: ***Agreed.***
7. Melody Maxim: Shortened accessory lines to avoid tangling and
confusion.
Mathew Sullivan: Not sure what this is?
Mike Darwin: ***Not sure what this either, but the shorter the better for
most lines. It makes hand-over-handing much easier and less necessary.***
8. Melody Maxim: Removed manometer port at AV loop.
Patient pressure is best monitored in vivo,
Mathew Sulivan: I agree.
Mike Darwin: ***This problem (monitoring arterial and venous pressures)
must be dealt with definitively and effectively. In the clinical setting of
fem-fem CPB the radial artery would typically be used to monitor pressure.
However, expecting SA personnel to reliably place radial artery lines is
unrealistic and too time consuming. Creating a routinely useable
(prefabricated) through-the-arterial-catheter monitoring line (using an
Intracath), or
buying Biomedicus arterial cannula with built in pressure monitoring lines,
is the best I can suggest. You may be able to get a reasonably good static
(non-dynamic) arterial pressure by placing an Intraflow-equipped line
distally into the femoral artery and ligating it there. Femoral collateral
circulation is very poor in humans, but it should be sufficient to give you a
static arterial pressure.
Whenever a central venous line is present (subclavian, Hickman, portal
cath, dialysis cath, etc.) you can use that for a reliable CVP. Monitoring CVP
will alert you to insufficient venous drainage, kinked or occluded venous
line, or an obstructed venous catheter..
All pressure lines must be equipped with intra- (Angio) flows to allow for
flushing and for priming of the lines prior to insertion. Virtually all
disposable pressure transducers have this feature incorporated into them; all
that is needed is an IV of saline and a pressure infuser. There are many
compact, reliable, self-calibrating pressure transducer-monitor systems out
there. Buy a good one and learn to use it.***
Melody Maxim: but if necessary, pressure can be monitored via the luer
lock on the arterial cannula connector.
Mathew Sullivan: Provided a three-way stopcock is already in place before
the circuit is primed.
Melody Maxim: Discuss. Is this acceptable for SAs purposes? What was the
purpose of the 3-way connector on the manometer port?
Mathew Sullivan: It is a multi-use port that allows for anything from the
removal of large amounts of air in the event there is a major problem,
sample taking, to injection of chemicals. I want to make sure I understand you
correctly. So you have a 3-way stopcock connected to the luer lock on the
arterial cannula connector, right? And you are saying this is a multi-use
port that allows for removal of air, sample taking, and for injection of
chemicals (drugs). In perfusion we are taught to NEVER inject anything through
the arterial side because of risk of introducing air. You always inject
chemicals/drugs into your venous reservoir. I believe trying to manipulate the
3-way stopcock while on bypass to either drawing blood sample or injecting
drugs is not a smart thing to do. Putting a purge line off the top (3-way
stopcock) of your arterial filter will allow you to draw arterial blood
sample and connecting another pressure monitoring line to a side port of the
3-way stopcock to your manometer will allow you to measure the arterial line
pressure. See the photo below:
Mike Darwin ***Melody is right. You should not be using this port for
anything in the field except to remove air prior to going on bypass. ALL
samples and drugs are added via the 5-gang stopcock. Addition of dye is for CPA
perfusion and must be done by an expert that is the only exception to the
rule and the only reason it is done is because there is no other way to get a
clean signal (the arterial filter dilutes the dye). NEVER use any port on
the arterial line (after the filter) for anything other than removing air.
Samples must also ALWAYS be taken from the stopcock assembly. There is no
reason to do otherwise since an arterial or venous sample withdrawn from the
stopcock assembly is not going to be any more or less accurate than one
taken from the arterial line near the patient. Taking a sample from the
arterial line is DANGEROUS and IRRESPONSIBLE. It is also guaranteed to result
in
air embolism sooner rather than later.***
9. Melody Maxim: Removed most 3-way stopcocks and syringes.
These are very easy to break off when packing, or setting up, the circuit,
and should be added after setup.
Mathew Sullivan: Some things can be assemble at the last minute such as
syringes and vacutainer ports, but I'm against not pre-attaching stopcocks. I'
ve been a party to more than one heated debate over who forgot to attach
the stopcock and the consequences resulted in anything from concerns
associated with the introduction of air after the start of procedures to not
being
able to get a sample at the last minute with the start of washout.
Having everything in place was done so at the request of Tanya because she
did not understand the kits well enough to know where to get everything
and put it together in the field. People such as Tanya will blame those who
make tubing packs for not making them complete, resulting in unwanted
problems in the field.
Mike Darwin: ***Melody is right but Mathew is more right. The stopcock
assembly must stay in place or it will, a) placed incorrectly (highly likely)
or b) forgotten altogether with people then going to the connectors on the
arterial and venous lines at the cannula to draw samples. Better to have a
broken stopcock assembly which they can see how to replace than none in
place at all. BTW, they will also not know to hook the arterial filter vent
line to the venous reservoir since most people in cryonics are relying solely
on the air separator on the filter. I was overjoyed when air separators
were first introduced on the Lekoguard because I saw cryonics personnel not
have any (bleed) line from the arterial filter to the venous reservoir.
Instead, they ran a monitoring line from the top of the filter to the waste bag
and they would only open the arterial bleed-line to remove macro-air that
had accumulated in the filter (and of course to let air out during
priming)!!!!!!!! Too incredible for words.****
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