Is PCWP normal or increased in ARDS?

[Knicks]

I have one source saying normal, and another source saying increased.


EDIT: Side-question..... can this analogy can be used to describe how squatting increases venous return?:

Think of squatting as squeezing a tube of toothpaste from the bottom; it pushes the paste [blood] to the Top of the tube [right heart ---> lungs). This is why squatting relieves the cyanosis of tetralogy of fallot.

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[jdh71]

I have one source saying normal, and another source saying increased.


EDIT: Side-question..... can this analogy can be used to describe how squatting increases venous return?:

Think of squatting as squeezing a tube of toothpaste from the bottom; it pushes the paste [blood] to the Top of the tube [right heart ---> lungs). This is why squatting relieves the cyanosis of tetralogy of fallot.

By definition ARDS needs 1) bilateral pulmonary infiltrates, 2) P/F ratio < or = 200, and 3) a normal PCWP or no clinical indications of left heart failure. We almost never put PA catheters in anyone anymore.

Your analogy is correct

 

[OveractiveBrain]

I have one source saying normal, and another source saying increased.


EDIT: Side-question..... can this analogy can be used to describe how squatting increases venous return?:

Think of squatting as squeezing a tube of toothpaste from the bottom; it pushes the paste [blood] to the Top of the tube [right heart ---> lungs). This is why squatting relieves the cyanosis of tetralogy of fallot.

Think about the pathology to help make it stick, to make it make sense. The PWCP is going to be given to you on the test to differentiate causes of "fluid on the lung" primarily Congestive HEart Failure from ARDS.

In CHF the pump is broken. Blood comes in from the right heart (through the lungs) and gets stuck there. The left heart just can't get the fluid out. The capillaries are intact. So, like water in a balloon, the blood vessels stretch, they distend, full of fluid. Eventually, the pressure from the walls of the capillary squeezes fluid into the lungs. Sad panda... fluid on the lungs. So, it should be no surprise that when you put a catheter with a baloon in the capilaries there, you are going to feel an increased pressure. Whether you as the student "feel" that pressure as hydrostatic pressure pushing water across the capillary or just the "back up of blood" isn't important. So long as you "feel" that failure leads to too much fluid in the vessels, increasing PCWP. I use this to prime you, since just about everybody gets CHF.

Now, ARDS is about leaky capilaries. This person is ICU sick, with fever, some terrible infection, something REALLY bad is going on here. Cytokines and other inflammatory mediators are going rampant, all over the body. The capillaries just open up. No pump failure, no back up of blood. Its like the Mississippi in Louisiana right now. They opened the flood gates and water poured into people's homes. Whatever fluid was in the capillary now can just flow into the lungs. "Feel" this as LESS fluid in the capillary, LESS pressure in the capillaries. So PCWP should be decreased (or normal).

In practice, the only person who gets a Swan is someone in cardiac crisis. These are the sickest of the sick in a tertiary center ICU. Chances are, the fact they've got heart failure is already known (so the Swan isn't needed) or they have a known cause of ARDS (like a blood transfusion or sepsis, so a Swan isn't needed). And, practically speaking "decreased or normal" for ARDS and "Increased" for CHF doesn't always 100% fly. There are many other vascular pressure and saturation readings that can be used to identify different cardiac conditions.

Knicks, I think you're studying for Step 2 right now, so you can ignore the broken summary in the "in practice" paragraph.

 

[OveractiveBrain]

By definition ARDS needs 1) bilateral pulmonary infiltrates, 2) P/F ratio < or = 200, and 3) a normal PCWP or no clinical indications of left heart failure. We almost never put PA catheters in anyone anymore.

Your analogy is correct

This is why squatting relieves the cyanosis of tetralogy of fallot.

I thought squatting in a Tet spell actually increased systemic vascular resistance, increasing aortic pressure, forcing more blood through the pulmonary artery (which, being stenosed has a larger resistance, and is why unoxygenated blood flows to the aortic side through the VSD). Im 98% sure this is true.

EDIT: Side-question..... can this analogy can be used to describe how squatting increases venous return?:
Think of squatting as squeezing a tube of toothpaste from the bottom; it pushes the paste [blood] to the Top of the tube [right heart ---> lungs).

Of course, I am 100% sure that squatting increases flow murmurs by increasing venous return (like a tube of toothpaste pushing the paste to the "cap" or the right heart). So the analogy is right, the specific example of the Tet spell I think is wrong.

Reconciling the "more blood, more murmur" of squatting against the Tet spell relief will bring together more complex cardiovascular physiology than either isolated in discussion. Both happen, just one dominates in any given scenario.

 

[Knicks]

thanks a bunch guys/gals

 

[dienekes88]

I have one source saying normal, and another source saying increased.


EDIT: Side-question..... can this analogy can be used to describe how squatting increases venous return?:

Think of squatting as squeezing a tube of toothpaste from the bottom; it pushes the paste [blood] to the Top of the tube [right heart ---> lungs). This is why squatting relieves the cyanosis of tetralogy of fallot.

I was under the impression that squatting relieved the cyanosis of ToF due to increased systemic vascular resistance leading to decreased right to left flow through the VSD and improved pulmonary vascular flow through the stenotic pulmonary valve.

In ToF, the right heart doesn't necessarily go to the lungs. Pulmonary stenosis and VSD --> deoxygenated venous blood to the left heart --> cyanosis.

 

[Knicks]

Of course, I am 100% sure that squatting increases flow murmurs by increasing venous return (like a tube of toothpaste pushing the paste to the "cap" or the right heart). So the analogy is right, the specific example of the Tet spell I think is wrong.

Yeah, I think so too.