EMCrit Podcast 45 – Acid Base: Part II

This is the second part of a 4 part series on acid base.

For this podcast to be optimally effective, you need to print out my acid base sheet:

EMCrit Acid Base Sheet

Here is the problem to work on for the next podcast:


I gave some shout-outs during the talk, here are the links:

  • The Air Medical Memorial honors those flight medics, docs, pilots, and nurses who have fallen in the line of duty.
  • Josh Mularella developed the free app call ERRES, search for it on itunes.
  • Casey Parker created a site for outback EM and Crit Care called Broome Docs.
  • Ivor Kovic donated three free codes to his cpr app, CPRPRO. Sign up for the mailing list if you want to enter to win one.



Need an Audio Only Version?
Acid Base Part II MP3  (Right Click and Choose Save as)


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  1. says

    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%

  2. Justin Koffer says

    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 ; )

  3. says

    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.

  4. Adam Drenzla says

    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.


    Love your work Scott !

  5. says

    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.

  6. Steve says

    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.

  7. Mike says

    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 doesn’t seem to be uniform agreement on how to calculate affective SID (various values for the valences of Mg and Ca) nor for effective SID… one that I found being: (HCO3- + (Alb/10)((pH x 0.1204) – 0.625) + (PO4-/0.323)((pH x 0.309)-0.469). Clearly too complicated for bedside use!

    Thanks and know that your work to make these podcasts is appreciated!

  8. Shannon Hamersley says


    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.


  9. Emma says

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

  10. Dallas Holladay says

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

  11. Bryan says


    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)?


    • says

      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.

  12. Andrew says

    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.


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