What would you do...

[Eydawn]

Why is the perfusion 5L and ventilation 4L? The concept as a whole makes more sense now thanks very much!! I guess I am asking why it isn't a perfect 1:1 ratio. I told you I hated my patho text... lol...

Wendy

CO EMT-B

[chbare]

The 5 litre and 4 litre values were somewhat arbitrary and simply numbers that I used to quantify the concept of 0.8 being normal.

The reality is that in an "ideal" situation, you would have near perfect matching.

The math involved is fairly easy:

Blood:

To calculate the content of oxygen contained in blood, use the following equation:

CaO2 = (1.34 * Hb * SaO2) + (PaO2 * 0.003)

The 1.34 is a constant that assumes every gram of Hb can contain 1.34 ml of oxygen. The 0.003 is a constant as well.

The answer will be in Vol% or ml per 100 ml of blood. In a perfectly ideal situation, you will have 20 ml per 100 ml or 200 ml per 1,000 ml.

Air:

Under ideal conditions with dry air, you will have about 210 ml of oxygen per every litre of air inhaled.

So, in an ideal situation, you can see that VQ matching should be nearly 100%.

However, in reality many factors such as gravitational effects, deadspace, and physiological shunting ensure you will not have a perfect 1:1 VQ ratio. The 0.8 is an average value that takes many of these factors into consideration. I hope that helps.

Take care,

chbare.

[Eydawn]

Oh my gosh. I am printing this out and keeping it! For the first time it totally makes sense. Thanks chbare! I AM SO STOKED! That has been bugging me for quite some time.

Wendy

CO EMT-B