Okay, I've looked in my books, searched online, and I still can't find the answer. Here's the situation: Where I work, we draw mixed venous samples from the Swan (as opposed to continuous SvO2 monitoring). Our intensivist ordered for a sample to be drawn from the proximal port and the distal port. When he got the results he said "What the heck? This lady's PA sat is lower than her venous sat?" And then went on to say that he thought she might have some shunting going on because of those numbers. What I don't understand is this--wouldn't it be normal for the blood to be LESS oxygenated in the PA normally? There isn't any gas exchange going on in the PA, correct? The blood hasn't reached the lungs quite yet. So why would he expect it to be higher in the PA??His next move was a 2D echo with bubble study to see if there was actually any shunting (there wasn't). So then I guess he came to the conclusion that her sats were due to her pneumonia. Just to give you background, this lady came in SOB, hypoxic, got a Swan, has high PA pressures (like 40's-50's), normal CVP, high wedge (around the 20's). First day she was admitted she ended up getting more and more bradycardic on us, ended up getting intubated as well. Thed mixed venous samples were taken before she was intubated. Also, the 2D echo showed moderate mitral regurg.