Can you help a student understand PCWP?

  1. I am trying desperately to figure out how PCWP measure Left Ventricular EDV, and I just can't wrap my brain around what I know must be a very obvious explanation.

    I'm clear on the normal values and all that business, but I'm not getting the anatomy of the set-up. If the PA catheter is inserted through the RA, RV and then carried into the pulmonary artery and wedged, how is that reflecting what's going on next door?

    I hope my question makes sense - I've dug out old AP books, everything and I'm stumped.

    Thanks in advance.
  2. Visit mandana profile page

    About mandana

    Joined: Nov '05; Posts: 352; Likes: 13


  3. by   EastCoast

    I'm sure you will get a dozen responses, however, this does a nice job of giving the theory and is quite straightforward. I learned swans a long time ago and i still carry around in my bag an article written quite similar to this.
    GOod luck.
  4. by   mandana
    Thanks for such a speedy response!

    Still not totally clear, so if anyone would like to add a thing or two, I'm willing to listen.

  5. by   hrtprncss

    scroll down to the wedge part, it's explained in simple terms
  6. by   dorimar
    ok , i hope i make this more simple and not more diffiuclt. The tip of the catheter sits in the pulmonary artery, and therefore picks up the pressures in the pulmonary artery, and those pressures behind the pulmonary artery (right ventricle), and in front of the pulmonary artery (left atrium). When the catheter is wedged, the balloon is up, and all the pressures behind the balloon(R ventricle) are occluded from the transducer, so we are only picking up pressures from the L side of the heart. Now during diastole, the mitral valve is open, so if we pick up pressure of the L atrium and the mitral valve is open we are also seeing pressures of the L ventricle. So, LVEDP (L ventricle end diastolic pressure) equals your PCWP (Pulmonarycapillary wedge pressure).
    Last edit by dorimar on May 20, '06
  7. by   mandana
    Thank you dorimar, thank you!

    You definitely clarified it for me, and now I can accept what they were telling me. My text book said, and I quote, "when arterial pressures become atrial the result is the LVEDP". It drives me crazy when text book explanations are A happens - MAGIC happens - B happens. I don't technically need to know why it works, I suppose, but I'm not happy unless I understand the magic part.

    Thanks again,
  8. by   mandana
    Quote from hrtprncss

    scroll down to the wedge part, it's explained in simple terms
    Missed your post the first time! Thanks to you too. Between all three of your posts, I think I've finally got it. Phew. Now onto my next obsession...

  9. by   ghmccart
    someone earlier said it perfectly. when in the wedge position and with an open mital valve you get a clear shot to the LV. SO how bout this, with out the ballon in wedge how can we tell roughly what the LV is doing pressure wise? PAD is essentialy the same thing in MOST circumstances as PAWP, same clear shot, same anatomical timing. some docs dont want their pts wedged and just say use the PAD, but watch out for mitral stenosis/BBB's/pulmonic regur etc.
  10. by   JOEYZ
    We use the PAD in place of Wedge in most cases.

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