This is the 3rd part of a 5 part series on acid base.
- You should listen to Acid-Base Part I first where you will learn about the underlying chemisty of acid base.
- Part II then delves into the underpinnings of the mathematics of acid base.
The Acid Base Series
- EMCrit 44 – Acid Base – Part I
- EMCrit 45 – Acid Base – Part II
- EMCrit 46 – Acid Base – Part III
- EMCrit 50 – Acid Base – Part IV – Choose the Solution Based on the Problem
- EMCrit 96 – Acid Base – Part V – Enough with the Bicarb Already
- EMCrit 97 – Acid-Base – Part VI – Chloride-Free Sodium
- EMCrit 227 – Acid Base Ep. 7 – Bicarb Updates, Quantitative Approach, and Prof. David Story
- EMCrit 380 – Acid Base Part VIII – Tris-Hydroxymethyl Aminomethane (THAM) for Acidosis
For this podcast to be optimally effective, you need to print out my acid base sheet:
EMCrit Acid Base Method
Here is the 1st problem from last podcast:
Here is the same patient after we treated his DKA:
Mike asked if there was any literature to support the simplification I am using to make the incredible complex quantitative formula more approachable. The answer is yes and here is the pdf you want to read:
Story DA, Morimatsu H, Bellomo R. Strong ions, weak acids and base excess: a simplified Fencl-Stewart approach to clinical acid-base disorders. Br J Anaesth. 2004 Jan;92(1):54-60.
Want an incredible program that will do all of the work for you and teach you about the quantitative method at the same time? Look no further than this incredible site:
Here is one of the must read articles by an EM Intensivist
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Editor-in-Chief, at EMCrit.org
An ED Intensivist from NY.
Professor
Nassau University Medical Center
No conflicts of interest (coi).
Professor
Nassau University Medical Center
No conflicts of interest (coi).
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Hi Scott,
Loving this simple method, makes acid-base understandable rather than just rote!
For the Aussie readers it is useful to change the “albumin correction” component to:
(42 – [albumin])/4 as we always get this is g/L – all works the same, but it seems easier without the decimal point.
C
Hi Scott – got a question. I see a lot of bad, non-compliant dialysis patients who walk around with K+ of 7 on a good day (unfun), then get septic on a bad day. If I am using this approach, and don’t wan to ignore the K+, do I just add in the K value to the Na – then subtract 42 instead of 38 to get the SID?
Let me know if this is right
Thanks
Casey
Yes, Casey that is exactly right.
Scott, in patients with significant hyperglycemia should the sodium be corrected for the hyperglycemia prior to the calculation of SID or does it make a difference? The acidbase.org calculator seems to do this.
Thanks.
Greg
For the acid base purposes, never correct the sodium, b/c the sodium level is real. Cl drops with the sodium to maintain SID. Correct sodium with hyperglycemia only to find out if the pt has hypo or hypernatremia.
Hello Scott! Im a medical student in Sweden, where emergency physicians doesnt exist as a speciality. I really appreciate you going through acid base disturbances in this systematic way. However there is something i still dont get(maybe the main point). For example, i saw a patient with chronic renal failure in the ED, who presented with weakness and tiredness thats been going on for about a week. The ABG came back with pH 7,14 pCO2 3,0 kPa BE -20 Na 131 K 7,6 Cl 115 Lactate 0,6 So the SID should be 131 – 115 = 16 right? SID –… Read more »
When calculating the SIG, particularly in DKA, is their any use of incorporating betahydroxybutarate in the calculation? If you are subtracting lactate in the setting of sepsis to take into account its presence in the “anion gap” it would seem logical that one could do the same with Bhob in DKA – does this line of reasoning play out in reality?
it does if you have a quantitative b-hydroxy. It comes right out of the SIG just like lactate as you say.
Anybody know the conversion for Alb in Australia? .25 perhaps?
Alb measured g/dL in US, g/L in Oz.
Thanks.
multiply US units by 10
I meant the “conversion” aspect i.e. multiplying by 2.5 in the US as Scott does above. Since the difference is 10, would the conversion in the formula be .25?
Never mind, I answered my own question: .25 X 40 = 10.
Piece of cake!
Hey Scott,
Absolutely love your blog, my favorite of all the medical blogs out there right now. Regarding the quantitative acid-base calculations, what do you suggest when we are doing calculations from blood gases, but do not yet have an albumin level (ie: in the initial phases of resuscitation)?
I learned the H-H way with the modification of adjusting the normal anion gap based on serum albumin, but that seems to be one of the very minor points when we were taught it as medical students, when in fact it is critically important.
Cheers,
Chris
nothing to do except to assume the albumin is normal
thank you for the new experience with Blood Gas stuff.. I know you made it very simple in this case.. what if I use the Na:Cl ratio (1.24-1.4) to look for Normal gap acidosis.. here it will guide me in the second blood gas (after correction of DKA), although it didn’t work well in the initial blood gas .. What do you think ?
ratios don’t hold up. Na 140 Cl 100 is VERY DIFFERENT acid-base wise than Na 70 Cl 50.
scott
Thank you for your response.. One more question: Will Winter’s formula (1.5XHCO3+8) give similar results of expected pCO2 here?
Dr. Weingart, As apart of our didactics today we went through your Acid-Base lectures 1-4 with the printed handouts. We then used your method and looked at a couple of random ICU patients’ labs and we tried to see if your method would have changed anything we did. In doing so we got a little confused. In one patient who had a profoundly elevated lactate (~10), we found that our SIG came to 15. We think this means that there are still 15 unmeasured anions floating around somewhere that we were unable to account for. Is this the correct assumption?… Read more »
Adam,
Can you send me the numbers for both cases and then I’ll take a look.
loving learning this quantitative approach to acid-base – thanks. Have a question: in your podcast you reunited H-H with quant approach by showing how you can just correct for albumin/lacatate and consider the SID with H-H and you get the same results as quant approach. However am I right in thinking that H-H will still have an inaccuracy because it uses bicarb instead of base deficit? The base deficit effectively takes out the effect of CO2 changes on bicarb. However using bicarb doesn’t. I’ve tried using both approaches with real patient gases and found them a bit disparate (after taking… Read more »
the results should almost always be identical. next time you have some real lab values that are drawn simultaneously (vbg, chem, and alb) check it out and comment here if they are disparate.
ok here are the numbers I have from the Australian branch of Janus General. 3 sets of results at different times on the same patient. Albumin was 45 (4.5 in your units) at the first draw. After that not measured but shouldn’t matter as the correction for albumin the same in each method. Time: 21:00 18:50 17:28 Units Ref Range pH: 7.18 7.20 7.29 (7.35 – 7.45) pCO2: 43 29 26 mmHg (36 – 44) pO2: 30 53 42 mmHg (80 – 95) HCO3: 16 11 12 mmol/L (20 – 26) Base XS: -12 -16 -13 mmol/L (-2 – 4)… Read more »
So 17:28: Quant method: 13+ (31-38) + 0.25 (42-45) – 4.9 = 13 – 7 – 0.75 – 4.9 = 0.35 H-H Method: 137-106- 12 + 0.25 (42-45) – 4.9 = 13.35 which is 1.35 above a normal AG rather than 0.35. Or I suppose if you say a normal AG is 11.5 by taking out lactate of 0.5 it is 1.85 above this. Depends what you call the real “normal” AG. In any case there is a slight discrepancy. When I calculate it for the the 2nd set of bloods at 18:50 I get SIG of 2.75 v’s AG… Read more »
Another question re the normal anion gap. I was confused re your podcast and other sources showing normal AG as 12 (+/-4) yet other sources were stating about 8 (+/-4). I now realise this is due to the modern day machines using ion selective electrodes instead of the older flame photometry resulting in chloride being measured about 4 mmol/L higher than previously as outlined in this recent article http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3681403/ This raises a couple questions: 1. When you explained the normal AG in the podcast with albumin occupying about 10.5, 0.5 for lactate and about 1 for other anions this calculation… Read more »
Ok, i just spent enormous amount of brain energy for days looking at all sorts of acid-base papers to understand this physiochemical Stewart approach of acid-base thanks to your lecture, and thank you for that so much. I’ve finally come to grasp this and I think I found better references for better way of looking at this. Although I think your approach is fine, I think the approach suggested by Gunnerson (Clinical Review: the meaning of acid-base abnormalities in ICU, Critical Care October 2005) is much better. They basically use the simplified calculation of SIG, derived from Dr. Kellum’s paper… Read more »
The formulae are exactly the same. If you understand why, then you are really starting to get this stuff. Of course, I’ve read Kyle’s paper. If that version works better for your mind, go for it. It is what I call the corrected Henderson Hasselbach method, which I mentioned during the podcasts–anion gap corrected for weak acids. This method won’t help unless you add in some analysis of non-sig acidosis as well.
Hi Scott! Thank you for making me understand acid base, in a simple and entertaining way. I have never understood it in medical school. Greatings, Annika (MD, Sweden)
so glad, Annika!
Jeremy Wininger,RN Critical Care Nurse Practitioner student, Duke University. Thank you for the great lectures on acid base.Working my way through the acid base articles posted on your site I came across a problem which implies the importance of the quantitative method. The problem comes from the article Facing acid-base disorders in the third millennium-the Stewart approach revisited by Kishen et al (2014). The article describes a patient scenario in which a High SID alkalosis is present (possible volume depletion from diuresis?) and a SIG Acidosis. Due to the 7.48 on the ABG this was overlooked and an AG was… Read more »
Hi Scott and Emcritters (or is it RACCers formerly known as Emcritters)?
I’ve just been though episodes I-III of acid base (published 2011) and wanted to remind myself of the equation for correcting anion gap for albumin. The first thing I found on searching this was the below article from Josh Farkas in 2014, which essentially states correcting for albumin is a waste of time.
I’m interested to know if this has changed your approach to calculating the strong ion gap (SIG)? It seems that a major reason for calculating SIG is to correct for albumin.
https://emcrit.org/pulmcrit/mythbusting-correcting-the-anion-gap-for-albumin-is-not-helpful/
think my comments in the comments section will lead you to my opinion on the flaw in the thesis of that post.
Hey Scott, what is that pen?! (fantastic video, I’m hooked on this new method!)
I have to disagree here. I find the Stewart method cumbersome and doesn’t add any clinical benefit from Henderson-Hasselbach. I do think though it’s good to understand all methods because it gives you better understanding overall. For example, for an anion gap metabolic acidosis, I quickly calculate the following in my head. 1. Calculate anion gap (AG) 2. Calculate delta gap = AG – normal gap (normal gap defined by albumin correction) 3. Expected HCO3 = 24 – delta gap (now compare to measured HCO3 from your chem panel, is there additional NAGMA or metabolic alkalosis going on?) 4. Expected… Read more »