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VQ Mismatch

jessica.krowka

Created on February 17, 2021

Nursing

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Transcript

VQ Mismatch

Jessica Krowka PhD, RN, CCRN

Title here

Picture A shows normal equal ventilation and perfusion

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VQ Mismatch

An extreme example is shown in picture B. Why does this affect gas exchange? Because the oxygen hemoglobin dissociation curve becomes flatter at higher levels of arterial partial pressure of oxygen.

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Lung set A operates around 100mm/Hg which is normal, but what happens in Lung set B in VQ mistmatch.

In B lungs, the right lung has a lot of blood, but not much ventilation so the oxygen content in the blood leaving that area is going to be quite low and the O2 saturation may be only 50%. What about the left lung? The PaO2 in that lung is going to be very high because there is so much more ventilation than perfusion to that lung. So that lung is operating way out at 150 mm/Hg.

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That’s barely any more hemoglobin saturation or oxygen carried than the healthy lungs (A). The blood from the poorly ventilated lung is carrying much less oxygen than normal, while the blood from the well ventilated lung is not carrying much more oxygen than normal. So the final result when you mix all the blood coming from both lungs back together is hypoxemia. The well-ventilated regions can’t compensate for the poorly ventilated regions because of this Curve

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Think about what you already know.

What is the normal level for oxygen saturation? What is the normal level for PaO2? Next look at this curve. See where the normal levels fit?

Thanks for your attention!