ARDS and V/Q/diffusion question

[babuchuck]

---

Members don't see this ad.

Can someone explain to me why ARDS is a ventilation defect?
I am really confused about this...but with ARDS since you have a hyaline membrane which would make it harder for oxygen to get to the blood from the alveoli wouldn't that be a diffusion defect? Goljan says it is ventilation and I'm still confused about the difference
I get that diffusion defects are generally fibrosis-related but wouldn't having ARDS also cause problems with diffusion?

Thank you.

 

[SeekerOfTheTree]

Can someone explain to me why ARDS is a ventilation defect?
I am really confused about this...but with ARDS since you have a hyaline membrane which would make it harder for oxygen to get to the blood from the alveoli wouldn't that be a diffusion defect? Goljan says it is ventilation and I'm still confused about the difference
I get that diffusion defects are generally fibrosis-related but wouldn't having ARDS also cause problems with diffusion?

Thank you.

The issue is in ARDS you have atelectasis so that results in reduced ventilation. Not so much a diffusion issue. With the aveolus collapsed because of the hyaline membranes you are having more of a ventilation issue than a perfusion or diffisuion issue. When you think of a diffusion defect think fibrosis.

 

[kstreet]

It is actually a combination of both. If you take a look at RR 283 it is both an intrapulmonary shunt due to the atelectasis and a diffusion abnormality related to the hyaline membranes and fluid.

Either way, blood is passing thru the vessels and not getting perfused and so it's a shunt.

 

[mastamark]

Can someone explain to me why ARDS is a ventilation defect?
I am really confused about this...but with ARDS since you have a hyaline membrane which would make it harder for oxygen to get to the blood from the alveoli wouldn't that be a diffusion defect? Goljan says it is ventilation and I'm still confused about the difference
I get that diffusion defects are generally fibrosis-related but wouldn't having ARDS also cause problems with diffusion?

Thank you.

Any time you have a situation in which your alveolar oxygen is much higher than your capillary oxygen concentration(which will be very low), you are dealing with diffusion issues. They never match up. Don't think of the wall as thickness as the only factor. Not having enough area will do it too. In ARDS you get destruction of alveoli, then you get stuff leaking into interalveolar sac, then your membrane. I hope that helps.