I have spoken about it for a while, but I've finally gotten it done: the acid-base podcast.
The podcast is going to be in 5 parts. They are segmented from a lecture I gave to my residents recently.
- Part I lays out the background of the quantitative approach
- Part II puts it in mathematical terms to allow calculation of acid base status
- Part III takes you through some real world examples
- Part IV discusses the Acid-Base Effects of IV Fluids
- Part V specifically discusses some of the Bicarb Controversy
The Acid Base Series
[display-posts tag=”acid-base-3″]
For the next part of the series, you will need a print out of this sheet:
EMCrit Acid-Base Sheet
This lecture discusses a quantitative approach to acid base management. This is also known as the Fencl-Stewart approach, the strong-ion approach or the physicochemical approach. It provides explanations for why acid base disorders occur in human pathophysiology. The classic method used in the USA is the Henderson-Hasselbalch (misspelled on my slides) approach. I find this method to provide no comprehensive explanation for why things are as they are. Through the quantitative approach, you can also understand the H&H approach and continue to use it with new insight.
This first part deals with the preliminaries. Part II will go into clinical applications.
For the next part of the series, you will need a print out of this sheet:
EMCrit Acid-Base Sheet
Want to read more?
- AcidBase.org
- Anaesthetist.com
- facing-acid-base-disorders-in-the-third-millennium
- Propofology Quick-Ref PDF
After listening to the podcasts, I recommend reading these articles
- Kaplan LJ,Frangos S. Clinical review: Acid–base abnormalities in the intensive care unit. (Critical Care 2005;9(2):198)
- Clinical review The meaning of acidbase abnormalities in the intensive care unit
- Facing Acid-Base Abnormalities in the Third Millenium
- (Am J Emerg Med 2015;33(3):378) Evaluation of acid-base status in patients admitted to ED—physicochemical vs traditional approaches
- Story D. (Open Mind) Stewart Acid-Base: A Simplified Bedside Approach. Anesthesia and Analgesia, 2016 (ePub ahead of print)
- 10 Acid Base Assertions
- A critique of Stewart and Bicarb approach
Need an Audio Only Version?
Acid Base Part I MP3 [Play] (Right Click and Choose Save as)
…
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Hey Scott,
From what I can tell, the first day your new Podcast comes out, it is not yet on the i-Tunes list. So the only way to listen to it is as a quicktime file on my PC. Is there another way? I usually just have to wait painfully to see that i-tunes has your latest but this is sometimes a day or two. Thanks for your hard work!
Matt
Refresh button on the bottom right of your itunes podcast screen will cause instant updates.
(Na + K+ Mg + Ca) – (Cl + lactate) = Answer to the Ultimate Question of Life, the Universe, and Everything
(when SID is normal)
C
I thought 42 was the ultimate answer to everything; remember your towel.
Exactly (if you fudge the numbers a little)
😉
C
Scott,
No mp3 version????
Mike
Added inside the post, just for you Mike.
Thanks Scott,
I am I-literate! But I have a towel
Mike
Great first part of the acid-base lecture. In fact, great website overall.
I start 3rd year of med school in July, and these lectures will no doubt improve my understanding of medicine and what goes on in the hospital.
Thanks!
Zach, thanks for the feedback. Get back to us and let us know how this version of acid-base fits in to what you learned years 1-2.
scott
Here they teach us H-H pretty religiously. What’s CO2 doing? What’s bicarb doing? What’s the pH? A little bit on anion gap. It all stays pretty superficial, and every discussion leaves you wanting more.
So, it’s nice to get a fresh perspective on the topic. Thanks again.
[…] spot this week go’s to Scott over @ EMCrit for tackling the tough topic of Acid Base in the Critically Ill. Part 1 in this series of podcast discusses a quantitative approach to acid base management. A […]
Hey Scott:
I light of this paper, do you guys still use NS at Hurst, or are you prefering LR. Just curious.
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This lecture is very helpful for my understanding of Acid/base coming from a 1st year. I really enjoy coming to the website to clarify and solidify many of the concepts we are covering in class.
thanks for the feedback, Christopher.
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[…] Using the physicochemical/ Stewart approach, the Strong Ion Difference (normal is 38) is markedly low (Na – Cl = 146 – 129 = 17). The causes of this are the same as the causes of NAGMA (see also EMCrit — Acid Base in the Critically Ill – Part I). […]
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Hey Scott, a quick question (but afraid its a long answer)
When the SID is decreased by giving NS, where does the H+ come from? Why does the decreased SID really cause an acidosis? It can’t be from the H2CO3 dissociating to H+ as that would also increase your HCO3-, right? I have been reading everything on Stewart’s approach that we have access to (Kaplan, Morgan, etc) but no one really explains it (and we can’t get a copy of the Stewart paper).
Thanks
Austin
Short answer–
Go right to the source:
http://www.acidbase.org/index.php?show=sb&action=explode&id=22&sid=24
Stewarts book for free. Short answer is H+lives attached to water molecules just waiting to emerge.
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[…] Using the physicochemical/ Stewart approach, the Strong Ion Difference (normal is 38) is markedly low (Na – Cl = 146 – 129 = 17). The causes of this are the same as the causes of NAGMA (see also EMCrit — Acid Base in the Critically Ill – Part I). […]
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My name is Olivier, MD at the university hospital of frankfurt.
So when you give diuretics (Furosemid, Torasemid) you will get low serum sodium leading to a small SID and thus acidosis but on the other hand there will be more sodium in the Collecting duct system in the kidney that will be taken into the principal cells causing a Transepithelial potential difference that will lead to H+ excretion by the H+-ATPase.
So will diuretics rather cause azidosis or alcalosis?
Hi Olivier,
it might not be a sound explanation but if you consider that the loop diuretics inhibit the NKCC which has a stoichometry of 1:1:2, you might loose more chloride than sodium and end up with a hypochloremic alkalosis.
I took this argument from this article in the NEJM: N Engl J Med. 2015 Jan 22;372(4):391-2
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Is there any way of estimating how much a mild element of renal failure would account for a certain strong ion gap?
Could you use the urea / BUN value to calculate this?
nope
and mild shouldn’t do it. that usually causes SID effects. To cause SIG, there is significant renal damage
Hi Scott.
In addition to this, is it possible to add a ketone concentration to our ‘unmeasured anions’ (to ensure there are no other unmeasured anions other than ketones)?
I can’t find a way to do this. From what I’ve read, serum ketone testing only measures acetoacetate and the ratios of hydroxybutyrate:acetoacetate:acetone vary, so ketone measurement is only semi-quantitative. Is this correct?
Thanks,
Stacy
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Dear Scott, I just discovered your great blog a few month ago and I’m trying to work my way through it now. Reading your Acid-Base-sheet I came up with a question with a question of no practical implications but i would be happy if someone could come up with a good explanation: You wrote that if the urine anion gap is negative one can rule out RTA. I found a paper (N Engl J Med. 2015 Jan 8;372(2):195 ) that put proximal RTA with a negative UAG. On the other hand Medline goes with you, on uptodate i could not… Read more »
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[…] Using the physicochemical/ Stewart approach, the Strong Ion Difference (normal is 38) is markedly low (Na – Cl = 146 – 129 = 17). The causes of this are the same as the causes of NAGMA (see also EMCrit — Acid Base in the Critically Ill – Part I). […]