### Cite this post as:

Scott Weingart, MD FCCM. EMCrit Podcast 45 – Acid Base: Part II. *EMCrit Blog*. Published on April 24, 2011. Accessed on January 16th 2022. Available at [https://emcrit.org/emcrit/acid-base-part-ii/ ].

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This Post was by the EMCrit Crew, published 11 years ago. We never spam; we hate spammers! Spammers probably work for the Joint Commission.

Chris Watford was kind enough to translate the problem for those not familiar with the old-school labs layout:

Na: 122

Cl: 88

BUN: 50 mg/dl

K: 5.3

Bicarb: 5

Creatinine: 2.1 mg/dl

Glu: 640 mg/dl

pH: 7.05

PaCO2: 14 mm Hg

PaO2: 96 mm Hg

FiO2: 100%

Man, this is it! Finally someone put this into a very compact and solid, digestable packet!

Well friggin’ done!

Bravo,

JP

I’m getting a SIG of 15, seemingly explained by DKA?

Don´t know if we were supposed to discuss that here, but since Brandon started …

I would say metabolic acidosis with a SIG of 11 (mmol/l ?), DKA being on top of the differentials. However: Why is the pCO2 so low? Compensation rules predict a pCO2 of 40-18=22 mmHg. I´ve learned that overcompensation does not exist. So associated respiratory alkalosis? Btw, do the compensation formulas apply the same way no matter what the FiO2 is? Suppose they should since pCO2 is not affected by FiO2 (=oxygenati0n) but only by ventilation …

looking forward to part III ; )

Feel free to discuss here and I will answer all comments in podcast part 3. Reason you two are getting different SIGs is I had to switch up the sodium from 126 to 122 to be able to make an important point later down the road. Folks that came up with a SIG of 15 got to the problem within the first few hours. There is nothing tricky about the problem; it just provides fodder for discussion.

For those who might not know about it but might be interested in it, there is a free online version of Stewart’s original textbook. You can also order the new edition of the book through the site.

http://www.acidbase.org

Love your work Scott !

Step 1: Get Labs! (See above post w/ lab values)

Step 2: pH; 7.05 -> acidosis.

Step 3: CO2; 14 mmHg -> respiratory alkalosis (consider compensatory).

Step 4: SID; 34 (Low-normal -> SID metabolic?)

Step 5: Lactate 0.5 (WNL)

Step 6: SIG: 18 + (34 – 38) + 2.5 (4.2 – 5.2) – 0.5 = 12 (SIG metabolic)

At this step I am considering DKA as the cause due to SIG metabolic acidosis and a BGL of 640 mg/dL (annnd the Hx that screams a diabetes problem).

I enjoy this process, very logical.

Do you have the audio only version for part 2? Only part 1 is posted.

Love the site, love the podcasts- I listen to them in my car and I have already learned a ton.

link in the post for audio-only is is now fixed. thanx for finding this.

Hi Scott. Thanks for these posts. The topic spurred my interest, and I’ve subsequently read 26 journal articles on the topic, as well as bought and read “Stewart’s Textbook of Acid-Base,” and numerous websites including http://www.acidbase.org. I have two questions. 1. I’m interested in any references to the PCO2 or HCO3- compensations using Base Excess. I have multiple articles outlining the Winter’s formula as well as others, but none have references to Base excess. 2. I’m wondering where you found references to use Base Excess in calculating theSIG? Clearly SIG is the difference between apparent and effective SID, but there… Read more »

Mike,

I will answer these excellent questions in part III.

Scott,

I absolutely love EMCrit. <3

Albumin in Canada is measured in g/L. so

(Base Deficit) + (SID – 38) +0.25[42-albumin{g/L}] – Lactate

should work.

Shannon

thanks Shannon

A deep dive into Acid/Base chemistry, physics, physiology, and medicine from our anesthesia friends can be found at: http://www.anaesthesiamcq.com/

Maybe a silly question, but I assume you calculate the Sid with the measured sodium not the sodium adjusted for hyperglycaemia?

Thank you, this acid base series was completely awesome! I wish I had learned this in medical school.

thanks brother

Hi,

Quick question about metabolic alkalosis.

The quantitative method is great for sorting out if there’s more than one source for a metabolic acidosis. Is there a way or calculation to tease out if there’s a superimposed metabolic alkalosis as well? In the above example for instance, let’s say the DKA was really contributing 21 of acid and not 11, but there was also an alkalosis contributing 10 of base giving us our SIG of 11…is there a way to detect this (other than the HH way)?

Thanks

Bryan, that will be reflected in the SID in the same way as the delta gap of H&H method. For instance let’s imagine you have 10 of ketones and before you got their gas, the pt got a ton of plasmalyte. They would have a Na of 140 and a Cl of 80. The BE would be 12. You would then correct the BE for the Na/Cl difference. Which would give a new BE of -10. This would tell you of the Met Alk as well as the SIG.

Would it be overkill to go ahead and get the albumin on all patients that you suspect Acid/Base Disorder in the ED? Should it be as reflexive as the VBG with Lactate and CMP that we normally do? I’m just wondering how my attendings will feel about constantly ordering albumins.

crit ill patients should have an albumin regardless of acid base. normal patients, we just assume its value is near normal

Is there a way to calculate how much a ketoacidosis is contributing to your gap based on the beta-hydroxybutyrate level?

Hi Scott

Great podcast has helped a lot understand how Acid-Base works and makes (almost) total sense. However I am now confused about SID vs Anion gap, as many other websites advise to calculate the Anion Gap using Bicarb, and differentiate between SID and Anion Gap. Can you help me understand the difference and the reason for not taking the bicarb into the equation? Thank you in advance for your help. Sam

hi,Scott.. i know that it has been a while since u made this podcast…but i need to ask question…so, pardon me for bringing this up again…but, first of all, i want to say that these are great lectures about stewart and they are really simple… THANKS!!! however, i do have question.. how can you come up with that SIG formula? in many literatures i have read before, the SIG formula is the difference between SID apparent – SID effective and in order to calculate that, we need to order few more labs with more complicated calculations than your formula. if… Read more »

Bravo!

Thank you

Veterinary student!

Somebody help my weak brain! Why in a “gap acidosis” is the SID smaller when the calculated AG would be wider? I can do the calculation, but can you explain to me what’s the rational explanation behind this?

One more question: I practice in a very low-resource setting. We never seem to have a measured bicarb available. Can calculated bicarb from the ABG ever be used in its place (I get that the beauty of this method is I never need to use the bicarb value, but just wondering…)

I’m trying to turn math into words..

I think if you break down the equation in Step IV, it translates into:

“Your patient has more acid than base (BD). What is that acid?

* is it chloride (SIG)?

* is it albumin?

* is it lactate?

* If it’s not those things, it’s other stuff (MUDPILES mostly)

Is this essentially correct?

Hi Scot, my name is Sonali Rao. I am one of Anes CCM fellow. I really enjoy your podcasts on almost everything. Specially I was getting hooked onto acid base quantitative approach podcast series. Unfortunately, part 2 onwards podcasts are not getting uploaded. I was wondering if there s any fix so that so many of ABG enthusiasts do not loose out on learning such high quality talks.

Best,

Sonali .