Can someone who knows PA cath's dumb this down for me?

  1. Trying to prepare for this critical care exam for a new job but my facility doesn't have Swan Ganz and they are so foreign to me Can someone help me to understand this -

    Understand interpretation of CVP and PA Pressure waveforms with Respiratory variation (position of waveform during inhalation vs. exhalation, during spontaneous breathing vs. mechanical ventilation)


    No luck with google!
  2. Visit chefjaxx profile page

    About chefjaxx

    Joined: Jul '14; Posts: 3

    6 Comments

  3. by   chare
    Quote from chefjaxx
    [...]
    Understand interpretation of CVP and PA Pressure waveforms with Respiratory variation (position of waveform during inhalation vs. exhalation, during spontaneous breathing vs. mechanical ventilation)
    [...]
    During spontaneous ventilation intrathoracic pressure is lowest during inspiration, and highest during exhalation. For the patient being mechanically ventilated this is reversed, intrathoracic pressure is highest with inhalation and lowest on exhalation.
    Quote from chefjaxx
    [...]
    No luck with google!
    An internet search using "CVP and PA pressure waveforms with respiratory variation" returned several helpful resources.

    Best wishes on your examination.
  4. by   offlabel
    Spontaneous Ventilation:

    1. Inspiration.

    Intrathoracic pressure falls. Pressure becomes sub-atmospheric, so atmosphere (room air) rushes into the lungs. Since the right atrium is an integrated structure of the thorax, the pressure inside of it falls as well so your CVP (right atrial pressure) falls. BUT...because the RA pressure falls, impediment to venous return falls too and just like air rushing into the lungs happens, blood moves more briskly to the right atrium.

    2. Expiration.

    Intrathoracic pressure rises, pressure becomes supra-atmospheric and the air in the lungs rushes out into the room. Since the right atrium is an integrated structure of the thorax, the pressure inside of it rises as well and the CVP (right atrial pressure) rises. This rise loads the RV.

    Mechanical Ventilation:

    1. Inspiration.

    Intrathoracic pressure rises (not falls), RA pressure falls, CVP falls (interestingly, the LV filling is enhanced).

    2. Expiration.

    Intrathoracic pressure falls and CVP rises.
  5. by   Chisca
    advanced-haemodynamics-36-
  6. by   chefjaxx
    Thank you all Very helpful.
  7. by   chefjaxx
    I appreciate the explanation. Much more understandable. Thank you!
  8. by   offlabel
    Quote from chefjaxx
    I appreciate the explanation. Much more understandable. Thank you!
    Except that there is an error in my explanation.... I wrote during mechanical ventilation, on inspiration, RA pressure (CVP) falls...that isn't true. Venous return falls because RA pressure (CVP) rises with intrathoracic pressure. RA pressure is an impediment to venous return. When it falls, venous return improves. When it rises, venous return falls. RA pressure follows intrathoracic pressure.


    Surprised no one called me out on that.

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