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.
- In part III, we will go through two actual problems and show how the EMCrit method plays out.
- Part IV delves into the acid-base of solutions.
- Part V specifically discusses some of the Bicarb Controversy

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

**Need an Audio Only Version?**

Acid Base Part III MP3 (Right Click and Choose Save as)

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### Scott Weingart

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## Comment Here

34 Comments on "EMCrit Podcast 46 – Acid Base: Part III"

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 – 38 becomes -22, which accounts for a little bit more than the whole BE. So there are no unknown component.

So my question is: Does the renal excretion of bicarb cause the SID to become low, or is the low SID in itself causing the acidosis? Or am i thinking in a completely wrong way?

Thank you for your podcasts, they are invaluable.

/David

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.

[…] brings us Acid Base: Part III bringing together everything he went learnt in part 1 & 2, with a case based approach in part […]

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.

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

[…] Shownotes: http://emcrit.org/podcasts/acid-base-i/, http://emcrit.org/podcasts/acid-base-part-ii/, http://emcrit.org/podcasts/acid-base-part-iii/, […]

[…] Shownotes: http://emcrit.org/podcasts/acid-base-i/, http://emcrit.org/podcasts/acid-base-part-ii/, http://emcrit.org/podcasts/acid-base-part-iii/, […]

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?

The next patient was someone who had a pH of 7.43 and their SIG came out negative, but no other metabolic issues were present. They were however having respiratory issues. Does your method work with these patients.

Also, we found that either way it would not have changed our treatments. The residents just wanted some clarification and some guidance and thought you may have a comment.

Thanks for all your work, I love the podscast.

Adam

Adam,

Can you send me the numbers for both cases and then I’ll take a look.

[…] Arterial Blood Gases – EMCRIT – Blood Gases Part 3 […]

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 into account albumin/lactate) and I believe it is due to the bicarb and base deficit difference. I even tried to calculate an expected bicarb by using a formula to take out the effect of the CO2 change but this didn’t solve the disparity.

Thoughts?

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.

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 no longer makes sense as it equates to 12 not 8. I note that the conversion factor for albumin is probably 2.3 more accurately rather than 2.5 but that still won’t make the calculation measure closer to the AG of 8. So how can we explain the newer AG of 8 with albumin/lactate?

2. Does the fact that modern daymachines are measuring cloride 4 higher mean when using the quantitative approach and calculating the SID we should be using 34 instead of 38?

Thanks Scott

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 not calculated. I applied your acid base sheet to this problem but want to make sure I am calculating this correctly. Could you help with this?

The values from the article are: 7.48/60.2/66.7/33.5 with a Base excess of +7.6. Na: 132 CL: 76 Albumin 1.8g/dl Lactate 1.9. Again all values come from the Kishen article. Thanks. Look forward to hearing from you.

[…] Check out the excellent podcasts from Emcrit about acid base in critically ill patients (http://emcrit.org/podcasts/acid-base-part-iii/) […]