Quote from Wile E Coyote
Thank you, but please note that I didn't encourage such either/or conclusions. I did go through the thought process on refining a differential Dx. This patient's management would better be driven by procalcitonin and serum protein levels. (Protein levels <1.0 are a strong independent predictor of SBP, so much that this is often a threshold for starting prophy Abx on chronic liver pts.)
Good information. But I wonder if there is still something you're missing. If you feel I'm wrong, please do explain...
The thing about this situation is that along with SBP in the differential diagnosis are several possibilities, at least from what we know so far.
1) The patient has no infectious process but is still in a hypoperfused state, most likely secondary to insufficient intravascular volume.
2) The patient has no acute disease process at all and is merely hypotensive within her compensated baseline range.
3) The patient has some other form of sepsis besides SBP, which is a possibility given that she lacks some of the common symptoms of peritonitis.
With this in mind, the first lactic acid level wasn't a way of asking, "does this patient have SPB?" or even "does this patient have sepsis?" It was asking, "is there something wrong here in the first place?" or "can we eliminate option #2 above?"
The patient was then administered fluid and volume expanders. A second lactic acid level was then obtained, and this second lactic acid could be thought of as a way to ask "does adding volume improve whatever is wrong in this case?" We still don't have a our differential diagnosis pared down to a single possibility, but the second level might give us hints about whether it would be a good idea to start abx empirically, transfer to a higher level of care, etc - especially if, like where I work, procalcitonin levels aren't performed in house anyway.
I suspect you may be right that a lactic acid in this particular patient of 2.6 wasn't even enough to answer the first question. Not being there (and not being a doctor), it's hard to know. Still, in this case, it seems reasonable to me to 'ask' not only whether the patient has SBP, but also whether that patient is sick at all. Once again, please challenge any arguments I've made that seem questionable to you.