ScvO2 readings in sepsis

[waterski232002]

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Does it make a difference where you draw a venous blood sample for a ScvO2? Can you draw it peripherally? Does it make a difference what port it's drawn off of from a central line (prox, mid, distal)?

 

[BKN]

Does it make a difference where you draw a venous blood sample for a ScvO2? Can you draw it peripherally? Does it make a difference what port it's drawn off of from a central line (prox, mid, distal)?

Actually did some of this back in the 80s in lab work. Basically the more central the better. Best mixed venous sample is from Pulmonary artery, then RV then RA. If from IVC or SVC it represents what's happening in lower body or upper body. If the low perfusion state is generalized, peripheral is ok. But given the physiologic changes is organ system perfusion to protect brain, heart, kidneys and gut, peripheral samples not acceptable (will read lowish) in most shock states.

 

[waterski232002]

That's what I assumed, but I couldn't find literature that gave explicit directions. Also, what port of a central line is best. The most distal port would ideally be best because it's closest to the RV, but can it get diluted if the patient is getting fluid/pressors through the more proximal ports? I would think not since venous oxygen saturation is a function of how much oxygen is dissolved in the serum????

 

[VentdependenT]

That's what I assumed, but I couldn't find literature that gave explicit directions. Also, what port of a central line is best. The most distal port would ideally be best because it's closest to the RV, but can it get diluted if the patient is getting fluid/pressors through the more proximal ports? I would think not since venous oxygen saturation is a function of how much oxygen is dissolved in the serum????

That would be your PvO2 (Partial pressure of oxygen dissolved in your blood. It should be basically equal to your PaO2. Its basically worthless unless your patient's HB is like 5 or something very low)

It won't matter if drips and fluids are running. Draw from the most distal port. Most PA caths have a continous Svo2 monitor so if you really wanna get nuts float one of those. How accurate are they? Dunno. They are good for trending. Sure you can follow it and see how its affected by changing CO/HB/O2/Hydration in your patient. However it isn't a great barometer for positive change in your patient, at least thats what I think.

 

[2bnevryorfis]

I have only utilized EGDT as a medstudent 3 times, but we used a special ScVO2 catheter each time. It looks similar to a regular triple lumen but it has an electrical cord that extracts the data from the sensor (similar to a pulse ox) on the distal tip, which was placed near the SVC/RA junction. Which is not as accurate as sampling from the pulmonary artery (which would be closer to a true mixed central venous hgb sat) but is more practical. The cord is then attached to its own special monitor so that you could see the changes in ScVO2 in real time. I believe the whole set-up is manufactured by edwards life sciences.

 

[Seaglass]

Bottom line - unless you are drawing it from their pulseless leg or arm then peripheral is good enough.

 

[BADMD]

Bottom line - unless you are drawing it from their pulseless leg or arm then peripheral is good enough.

Having looked at simultaneous samples drawn peripherally and centrally, I certainly wouldn't trust a peripheral stick to make treatment changes when doing or considering EGDT.

Frankly, it is pretty hard to do EGDT without a central line, since the first goal requires a CVP measurement.