VBG=ABG, but I "know" my TLC was in the vein!

[Blake300m]

So I had an older lady in septic shock last night in whom I placed a left subclavian TLC. She was frail and had easily identifiable landmarks - I got back nice dark red blood (witnessed by myself and a nurse present) on my first stick without any complications; prior to threading the wire I checked for any pulsatile flow and got only a mild dribble; placed the wire, dilator, and TLC without any difficulty and secured line at about 18 cm (she was pretty small). Drew back dark red blood on all 3 ports. Post procedure CXR showed the line to be, to my eyes, in the SVC, although prob 2-4 cm short of the SVC-RA junction (but not anywhere near the aortic knob). Fluid and PRBC flowed easily through the line with no resistance, and we had Levophed running for about 30 min to 1 hour until I saw the blood gas drawn off the line, which looked arterial - oxygen pressure was 230 and oxygen saturation was 95% (pt was on 50% FiO2 (trach/vent dependent) with pulse ox sats in the mid 90s). Concerned now that the line was arterial, we checked the pt's left radial pulse, which was strong and equal to the right. We turned off the pressors temporarily and checked simultaneous gas off the subclavian line and a gas off the R radial artery. These 2 gases were essentially the same as far as pH and pCO2, but the oxygen pressure was 130 in the radial artery stick and 170 in the subclavian line (the 2 gases were drawn no more than 2 minutes apart, with no change in vent settings or hemodynamics during this time). I rechecked the CXR, which looked like the line was in SVC. We hooked up the subclavian line as if it was an arterial line but 2/2 technical difficulties were unable to get any waveform (venous or arterial). We checked for any pulsatile flow but again there was none, and were able to drip normal saline slowly into the line without any resistance or backflow.

So my question - in the face of everything telling me the line was in the vein, except for the gases (which granted is a pretty huge except), is it possible to have essentially similar venous/arterial blood gases? My theory was that this pt had failure of her electron transport chain 2/2 sepsis and was essentially unable to utilize any oxygen (mitochondrial failure, I can't quite remember the exact name for this(, thus explaining the similarities bw the gases.

Any thoughts/similar experiences? I think that I will start transducing all lines I do now without ultrasound guidance (I think it's likely unncessary for lines that you do real time US guidance, ie IJs). Although if the flow is not pulsatile or briskly flowing when you remove the syringe prior to passing the wire, are you really going to gain anything extra by transducing?

Thanks all!

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[EMCC]

A few things:

Frail, cachetic people are harder than slightly obese people to get into the vein. So, 'easy' means little in them.

If this patient is hypotensive and SIRS, then yes, arterial blood can look venous when 'dribbling out.'

Regardless of venous or arterial placement of the catheter, fluids and pressors will flow in easily.

Pulses will still remain equal after placement of a catheter in the artery--think about the size of the TLC versus the size of the subclavian artery.

Why are you using a TLC as a resuscitation line?

18 cm for a LSC seems right, but the aorta lies right next to the SVC. On an AP CXR would appear similar. Heck, I have had azygous lines that looked good on CXR.

More important than the PaO2 is the SvO2/SaO2. Nevermind, you posted it.

Sounds like you were in the artery based purely on the numbers you gave. Again, mitochondrial paralysis will have an elevated SvO2, but the SaO2 would look similar if you are the artery. The Pulse ox correlated with the SaO2--if it quacks like a duck, it probably is...

Not trying to be a prick, but these are things to think about and defend when posting a case like this. "Septic" old ladies (and men) confound even the best of us more often than not... It is definitely not easy on first blush to fully sort out what ails them.

Tranducing the line can be helpful, but under non-emergent conditions. Sounds like this wasn't, but if your nurse is not familiar and facile with setting up an A line (many EM nurses are not) then it will not help you--as you tried later on. One thing you can try, is simply hook up the needle to sterile IV tubing and lift up the tubing into the air. Arterial blood should raise the column, unless the patient is profoundly hypotensive, in which case you may get burned on artery versus vein. Heck, it has definitely happened to me in the past! (Wont' mention how many times...)

 

[AmoryBlaine]

So it popped through into the subclav aa. at some point, that's all there is to it. You cannot get a PaO2 of 230 in the subclav vein or a sat of 95%.

You can think about weird fistula situations if you want but in this case I would just trust the gas and use the line as a a-line or nothing.

 

[BKN]

So it popped through into the subclav aa. at some point, that's all there is to it. You cannot get a PaO2 of 230 in the subclav vein or a sat of 95%.

Oh, I believe you can. Some patients with sepsis have a high cardiac output but little oxygen extraction (decreased A_V O2 difference). The description sounds like it was in the SVC. The correct move is to attach a monitor and check the pressure. Failing that, a very direct approach is to put the patient on a fluoroscope and shoot some dye.

 

[wook]

You can potentially get a paO2 ABG = VBG in cyanide poisoning....just an interesting side note and not applicable in this case unless she was in a housefire or someone trying to collect life insurance policy.


Thanks.



Wook

 

[Punisher]

i'm a huge fan of ultrasound guidance... less so for the initial needle path, but more to confirm the placement of the guidewire in the vein. you could try placing your subclavian lines with ultrasound guidance (few people mention this article):

Subclavian venous catheterization: greater success rate for less experienced operators using ultrasound guidance.
Crit Care Med. 1995 Apr;23(4):692-7.
http://www.ncbi.nlm.nih.gov/pubmed/7661944

or, if the central line is already placed, try to fit the ultrasound probe between the clavicle and the central line to try to visualize the tubing... not sure how well this works though.

 

[Hernandez]

Although if the flow is not pulsatile or briskly flowing when you remove the syringe prior to passing the wire, are you really going to gain anything extra by transducing?

Thanks all!

personally, I have everything but the transducer hooked up and if i'm not 100% sure, I'll have the nurse finish setting up the monitor and I'll hook up the (sterile) extension pressure tubing and transduce a waveform right off the needle. the times it helps are pts with high venous pressures who are vented, they will have pulsitile venous sticks, and the septic pts who are hypo-perfused and the blood is just a tinge redder than I think it is (I've caught myself twice in the last three months on fem sticks) and just to confirm when you have someone who's supra-oxygenated on the vent with really bright venous blood. in most pts, it's not needed, but I have the tools handy to check quickly if I'm not sure. I'll transduce right off the needle before i dilate

 

[Hernandez]

Tranducing the line can be helpful, but under non-emergent conditions. Sounds like this wasn't, but if your nurse is not familiar and facile with setting up an A line (many EM nurses are not) then it will not help you--as you tried later on. One thing you can try, is simply hook up the needle to sterile IV tubing and lift up the tubing into the air.

after several incidents of operator error in dealing with monitoring in the ICU, I've made a point to know how to set up all the equipment and trouble shoot it myself, I pretty well set up all my cvp/art line transducers anymore just to save time from having to wait on the nurse anyways.

it once took me and a young nurse half an hour to realiZe that the reason the cvp wouldn't work is because she had put on the luer lock hub in between the circuit and you cant transducer off that...