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P-Video: Rule of 15 in anion gap metabolic acidosis



You have a patient with an anion gap of 30 and bicarbonate of 10 mEq/L. You also determine on VBG that the patient’s pCO2 is 25 mmHg. What trick of the trade can you use to quickly determine whether this low pCO2 is an appropriate compensation of the primary metabolic acidosis? Dr. Jeremy Faust and Dr. Corey Slovis explains the quick “Rule of 15”.

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Michelle Lin, MD
ALiEM Editor-in-Chief
Academy Endowed Chair of EM Education
Professor of Clinical Emergency Medicine
University of California, San Francisco
Michelle Lin, MD
Michelle Lin, MD

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  • Joao

    Venous blood gas? Isn’t it arterial blood gas?

    • jeremy faust

      Hi Joao: Thanks for commenting! The venous blood gas (vbg) is really excellent for 99% of patients and you almost never need to get an abg. According to Dr. Slovis, for 99% of patients VBG pH will be within 0.01 and 0.03 of the arterial pH (i.e. 7.40 vs 7.38). I don’t know the data for this but if someone else does, that would be great.

  • Gustavo Montanha

    Thanks for the great info and cool video – amazing people out there. I have a question unrelated to the content by itself but that shows in the video: what is that sort of “table” that keeps showing up with the 6 “cells” and the < showing the number 400 and 500 on the right. I see it's a way of organizing values from the lab results but I'd like to know a bit more about it, such as what's the name of that, who created that and why and how to use it effectively. Thanks for everything!

  • Steve Piriano

    I have found this issue a bit confusing. The Rule of 15 makes it so clear. It is now easy to figure out if there is either appropriate compensation or a secondary process occurring. Thank you!