Swan question from a new CCU RN

Hello Allnurses!

I'm new in CCU and had my first pt with a swan last week. I work nights so it was my job with my preceptor to draw a "mixed-venous" specimen from the PA lumen on the swan to run an svo2 to calibrate my swan machine because it is the continuous cardiac output type of swan(not sure if that really matters...I'm VERY green when it comes to swans).

My question is, why is it a "mixed venous" specimen when it comes from the PA lumen? Isn't that the end of the road for blood before it hits the pulmonary circuit and becomes oxygenated?

Thanks for any help you can provide,

Kool-aide, RN

[DogLover17]

deleted, I was very wrong. Love learning from this site!

[sevo87]

The term mixed is what is throwing you off, the blood is all oxygen poor. The svo2 value tells you how much oxygen the body tissues are extracting, basically it tells you how much you hAve left over if you will. It is not a 'mixture' of oxygenated and deoxygenated blood.

[MunoRN, RN]

By "mixed" it refers to mixed venous blood from all sources; the superior vena cava, inferior vena cava, and coronary sinus.

An ScvO2 is a sample of venous blood usually only from the superior vena cava, which is what you get from a regular central line or PICC since the tip is usually upstream from where the inferior vena cava and the coronary sinus empty into the right atrium.

[kool-aide, RN]

Thanks to all for your replies! This makes so much more sense!