Hey everyone, I'm Brandon Odo.
And I'm Brian Bulling.
And this is Critical Care Scenarios, the podcast where we use clinical cases, narrative, storytelling,
and expert guests to impact how critical care is practiced in the real world.
Alright everyone, welcome back to another Turbo.
It is Brandon Odo.
The topic today, central lines or central venous catheters compared to peripheral catheters.
What do these terms mean?
What is this distinction and is it important?
You might think this is an arbitrary cutoff.
In fact, it is.
We use these terms in a way that is very specific.
A line is either central or peripheral.
However, it's not really clear if you get down to first principles why we make the distinction
and if it is actually, as they'd say in philosophy, a natural kind.
Is this a category that arises from some in a intrinsic characteristic of the things or
is kind of a made up category meant to serve some purpose, but it's really artificial?
So starting with the question of what defines a central versus peripheral catheter, that's
pretty clear.
Essentially, if you draw a box around the abdomen and thorax, so at the upper chest here, it's
at the axilla where the arms meet the torso and at the lower abdomen, it's at the groin,
the femoral or inguinal crease where the legs meet the abdomen.
When you get proximal to that line, so into that thoracobdominal case, then you are talking
about the central space.
And we're talking about a central line when you have a catheter that terminates within
that box.
It doesn't matter where it started, but if that's where the tip lands.
So if you place a central line into an internal jugular vein, it's starting outside of that
box, but the tip of it is ending inside.
It's ideally at the cave-o-atrial junction right before you enter the heart.
But certainly if you get past the neck and you get into the chest, you would call it
a central line.
A femoral line starts often right in that femoral crease, but it could be on the leg,
but the tip, as long as it is past that juncture in somewhere in the IVC or perhaps somewhere
in the iliac vein, we'd call it central, subclavians and so on, likewise.
So that's clear enough.
Why do we make the distinction?
I don't know.
Probably the main reason is due to infectious risk.
And I think a good analogy here is comparing a deep vein thrombosis compared to a clot
in a non-deep vein, a superficial thrombophylobitis.
You know, these are both clots in veins.
Why do we treat DVTs as more serious important things?
And we do.
We say they should be anticoagulated.
We say they're at risk of embolizing, whereas superficial clots seem like they're no big
deal.
Maybe they put a compress on it or something.
So this is not the same deal because a deep vein is not the same as central veins, but
it may be an analogy here in that you could ask, what's the difference or both veins?
So I think the important difference here is infectious risk.
The data suggests that central venous catheters are associated with a lot of morbidity and
even mortality if they develop infections.
So these are clapsies or central line associated bloodstream infections.
Clearly patients do worse when they have them.
Whereas infections of peripheral catheters don't seem like they're quite as significant.
Now there are caveats here.
All IVs can get infected and they even can develop serious infections.
A serious, like, sub-purative infection of even a regular peripheral IV can actually kill
people.
It's not very common, but it can happen.
So you know, what's the distinction here?
In some ways it is probably an arbitrary one, right?
When does that central line become a peripheral vein or vice versa?
It is probably some kind of a continuum.
I would guess that probably the continuum involves the size of catheter.
Central lines as a rule are longer.
The more catheter you have that is intravascular, probably the more surface area there is that
can come in contact with circulating bacteria and forminitis for infection.
Well catheters are very short and just surface area wise there's less of it.
Maybe it also matters whether they're in a central circulation which gets more blood
flow compared to a small peripheral vein which only sees blood coming from that one
part of, let's say, the hand.
Maybe there's just less opportunity for bacteria to get there.
I'm hypothesizing here.
The real reason that we make this distinction is because the data supports a difference
in outcome.
But if you're a kind of rational thinking person, you could still ask these questions.
Questions like if you place a catheter just inside the central circulation or just outside
of it, does that suddenly change its infectious risk?
So for instance, midlines are a in-between catheter that is longer than most people
would call peripheral but does not reach the central circulation.
That's really the definition.
Basically they're putting the upper arm.
So if I place a midline here and it terminates just before the axilla, then great.
It's a midline which is just a form of peripheral catheter.
If it terminates a little deeper and it gets past the axilla, technically we would have
to call that a central line.
But does that catheter for being a centimeter longer or even not longer just placed more
approximately so it gets a little deeper, is it suddenly at higher risk of infection?
I don't know the answer to that.
And that applies to just about anywhere.
For instance, you can place a lot of center lines in different places in their vessel
and I don't know if that changes the infection risk.
If I place a femoral line quite distally on the leg, I might even be placing it into
a vein which is considered superficial, like the superficial femoral vein.
And it may continue deep enough far enough to reach the central circulation, but maybe
it doesn't.
Maybe it terminates before you kind of cross that line.
I don't know if that affects the infectious risk or not.
I don't know that this has ever been studied.
You can also then ask the question of length notwithstanding and tip notwithstanding.
What about subcutaneous distance?
So why is a pick line considered in certain contexts to be lower risk of infection than
an ordinary central line?
Well, it's because even though it's very long and by my theory here, length of catheter
being intravascular should increase the infectious risk.
It also has a very long section of peripheral or even subcutaneous distance.
So to infect the deep portion of a pick line, most of these infections originate at the
skin, tunneled down around the catheter and kind of creep along it to the central circulation.
In this case, I asked to start all the way out on the arm, navigate along the bacilic
vein or whatever it's in until it finally gets to its distance.
Maybe that's the reason.
And pick lines, by the way, do not have a lower risk of clapsi when they're used in
the inpatient setting, although they do in the outpatient setting.
What about tunneled catheters?
So a tunneled line like you might use for long-term central access or dialysis access?
Those do have a lower risk of infection.
And again, it's probably because you tunnel under the skin and subcutaneous tissue for
a good distance.
And that is a lot of distance that bacteria have to creep along.
And this is especially true because when they tunnel it, it makes a very tight connection.
There's a cuff around the catheter.
And so it's just it's like a barrier for the bacteria to traverse.
These are all subtleties that are not really captured in that deep versus peripheral question.
You might also talk about arterial catheters.
Is there a difference in infection risk between a peripheral and central arterial line?
We don't always make that distinction, but you can ask the same questions.
And it's harder to say because people aren't even clear on the infection risk of arterial
catheters in general.
It's by and large pretty low, which doesn't mean it's zero.
And people do act as a more central one.
So femoral or maybe an axillary arterial line compared to a radial probably are somewhat
higher risk, but you're getting into much vaguer areas of data when you talk about this.
So these distinctions are ones that you can't ignore if for no other reason they get into
definitions in things like are we classifying this infection as a central line infection,
which has real implications on things like reimbursement and quality metrics that matter
a lot to hospitals.
But if that weren't the case, would we still ask these questions?
I think probably yes, but I think the distinctions would be a lot more vague or at least more
continuous and gradiated versus clear cut.
Yes and no.
Thanks to ThinkAbout.
Talk to you next time.
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