Am I correct about shunt and dead space. Please correct me.

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Any defect in ventilation/perfusion leads to V/Q mismatch that leads to hypoxemia and alveolar hyperventilation and hypocapnia(Respiratory alkalosis). If the hypoxemia is not corrected, muscle fatigue and respiratory failure ensues. To correct the hypoxemia seen in V/Q mismatch, we can increase the FiO2 as long as the ventilation defect is not large enough to cause a shunt.

Dead space is when there is absolutely no perfusion. This leads to alveoli values of PAO2 = 150/PACO2 = 0mmHg. While I was reading online, it said there won't be hypoxemia in cause dead space but hypercapnia. Isn't dead space a V/Q mismatch and by definition a hypoxemic condition and how can there not be hypoxemia in dead space.

Please see if there are any holes in my understanding and help me fill it. Thank you.

 

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If I can add one more point to this... since there will be hypoxemia(increased A - a gradient) in diffusion defect also(which is not V/Q mismatch), the arterial values will be the same as V/Q mismatch. How can we differentiate between the two? By DLCO? If not DLCO, is there anything else? Am I missing any key concept here or is my concept completely skewed? Does 100% oxygen correct hypoxemia in diffusion defect?

 

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anyone?