Comments on: Part 2 of the acid-base problem

By: Blood Tests Save Lives If You Know What To Look For - Better Health

Blood Tests Save Lives If You Know What To Look For - Better Health — Thu, 11 Feb 2010 15:58:04 +0000

[...] in understanding. For me, their evaluation is mostly automatic. Some clinical scenarios are more complicated than others. But knowing your way through acid base will save lives your entire [...]

By: Blood Gasses Save Lives If You Know What To Look For - Better Health

Blood Gasses Save Lives If You Know What To Look For - Better Health — Wed, 30 Sep 2009 23:07:08 +0000

By: Pro Nephros

Pro Nephros — Sat, 29 Aug 2009 04:58:04 +0000

I essentially agree with Happy Hospitalist above. You used the delta gap to estimate that without the ketones/lactate, serum bicarbonate would have been 34. What you have now looks like a non-gap acidosis, which of course could not have co-existed with the metabolic alkalosis you diagnosed when she came in. But what if this isn’t metabolic acidosis, but rather a baseline and pre-existing respiratory alkalosis from her liver disease? The original metabolic alkalosis was simply more severe than you thought. As HH points out, one could test this hypothesis by getting an ABG now, which I would predict will show a pH an the normal range with a low pCO2.

By: Happy Hospitalist

Happy Hospitalist — Fri, 28 Aug 2009 20:22:56 +0000

The anion gap is gone. You replaced the fluids and the metabolic alkalosis is gone from the vomiting. But your still left with a non gap metabolic acidosis. I suspect this is probably a compensatory response to the respiratory alkalosis your patient experienced while trying to blow off anions for the last two weeks. Now that she isn’t breathing so fast, her CO2 is building up, relative to the delayed kidney response, perhaps giving her a “relative respiratory acidosis”.

A gas would be helpful at this point.

By: John

John — Fri, 28 Aug 2009 02:28:32 +0000

I think I see where you’re going with this:

We’ve corrected the gap but still have an acidosis, thus now she has a normal anion-gap acidosis. When I see this I immediately look to the history for any diarrhea thinking about GI bicarb loss and I look at the PMH and Meds thinking about the three types of RTA’s. I’d probably check urine lytes to calculate the urine anion gap which if positive would tell us the kidneys are not appropriately excreting acid. You can also get a normal anion-gap acidosis secondary to a high volume normal saline infusion, which she had and I’m guessing is the cause. I may not be remembering correctly why this happens, but I think it is the excessive chloride that causes renal bicarb wasting?

By: cory

cory — Thu, 27 Aug 2009 18:38:02 +0000

I imagine one of the things you’ll have to do is replenish her potassium.
I don’t know if that’s the answer but to go to a tangent, what possible rationale is there for not drawing blood gases? In a patient with a bicarb of 7?
The test gives a huge amount of information – far more than virtually any other test in this type of situation (‘m sure she got a U/A and a CBC)
It takes a tremendous amount of guesswork out of the differential gives us an idea of the severity of the problem and how sick the patient might be.
This seems to be the trend- no one wants to draw blood gases anymore – even in cases where they are obviously indicated.
You are an educator -perhaps when you are done explaining this problem – which is after all an acid-base problem, you can explain this trend away from ABGs, which has a secondary effect that residents no longer understand their interpretation. And unlike some diagnostic tests which get superseded by better ones, there are few tests better in sick people than blood gases. What’s going on?