CVP/ BP and mechanical ventilation

[lmarti10]

I work in a cardiac ICU, taking care of patients immediately post-op. my question is:

if mechanical ventilation decreases venous return, why does a patient's CVP drastically go down after extubation? I've also noticed a lot of times their BP will drop as well and they will require norepi gtt.

[NurseyB]

I'll take a stab in the dark, though I may be wrong. Just thinking out loud here...

For CVP, they are probably taking more, and shallower breaths (due to pain and the loss of ventilatory support), which is going to decrease intrathoracic pressure. Because of the seeming decrease in preload, the HR picks up to maintain CO and meet their O2 demand. BP falls in response to the increase in HR.

I'm not an expert critical care nurse, and I have exactly zero experience with hearts, but this is how I think through it. Hopefully some smarty will come along that can confirm or refute this.

[offlabel]

CVP (right atrial pressure) and venous return are two different things. In fact, they are inversely proportional. That is, the higher the CVP (RAP), the lower venous return. This is because the force that drives venous return (something called the mean systemic filling pressure, MSFP) must overcome the CVP (RAP).

So your observation is correct. Venous return increases.

As to the need for NE, it might be necessary to raise vasomotor tone briefly as the hemodynamics adjust to the change in venous capacitance going from PPV (or CPAP) to SV. A little volume might be required as well.

[PaSSiNGaS, MSN]

When someone breathes normally it is negative pressure in the chest. During mechanical ventilation it is with positive pressure. The positive pressure is generated over all pressures which increases the CVP

[ejnjj143]

Thanks for that info. I was helping with an open heart and got schooled why the CVP was higher in intubated pts vs. Non-intubated