drawing a mix venous blood sample

[blee1]

took a hemodyn class and was told to draw a mix venous sample over 1 minute. Why?? People around my unit are saying youll pull arterial blood (ie oxygenated blood) and ruin the sample (doesnt make sense, the cath is in the PA with venous blood). Can someone clarify please..

[estherojin]

"Vigorous aspiration can cause arterialized blood from the pulmonary capillary to be drawn into the syringe, falsely elevating the result."

[blee1]

"Vigorous aspiration can cause arterialized blood from the pulmonary capillary to be drawn into the syringe, falsely elevating the result."

where are you quoting this from?

[seanpdent, ADN, BSN, MSN, APRN, NP]

I don't have any references, but just the mere fact you are drawing a 'mixed' venous blood, I believe the slower you draw it up, the better, or more accurate the sample because you are allowing 'more' of the mixed venous blood flow through the catheter thus a broader range or better mixture of a sample.

That's my theory and I'm sticking with it. :)

[estherojin]

I'm quoting from the AACN procedure for critical care for under the section "Blood Sampling from Pulmonary Artery Line". It's a great reference to have for your nursing library.

[lindarn]

You ARE drawing the sample from the DISTAL port of the Swan, aren't you? And a simultaneous sample from the arterial line so that the docs can calculate the prescense of a shunt?

Several years ago, I had a heated discussion about this with the "know it all" of the unit, if you know what I mean. She INSISTED that the mixed venious sample came from the proximal port, not the distal port, because we never "draw blood from the distal port". She was an older woman who was in business before she decided to become a nurse. She was a real management "suck up" and was "ALWAYS RIGHT!".

Anyway, just make sure that you draw it from the correct port.

Lindarn, RN, BSN, CCRN

Spokane, Washington

[estherojin]

mixed venous is drawn from the distal port that sits in the PA. it's called mixed venous because it is a mixture of the venous return from the SVC and IVC. in the cath lab, we used to do shunt runs and have seen PA samples vary due to aggressive aspiration techniques. if you pull too fast, i think you can end up wedging the catheter and sample from the LA (which is arterial blood).

[diosadelsol, ADN, BSN, MSN, RN, APRN, CRNA]

Just curious, Estherojin, how are you wedging the catheter while drawing a SVO2 sample? I don't know if I'm missing what you're saying, but out of the millions of times I've drawn one of these samples I've never had the problem with wedging the catheter. Please clarify.

[suanna]

Pulmonary arteries are springy plyable little things. If you pull back too fast the negative pressure can collapse the pulm artery around your catherer tip and allow you to pull back oxygenated blood from the pulmonary bed. I think you would have to hook it up to a shop vac to pull blood back from the L heart.