Yilin Zhang, MD
Brandon Fainstad, MD
Expert review pending.
1. Identify the primary acid-base disorder on an ABG
2. Create a differential for different primary acid-base disorders
3. Calculate the anion gap and delta-delta
4. Calculate expected compensation for the primary acid-base disorder
5. Practice reading ABGs
Plan to spend at least 30 minutes preparing for this talk by using the Interactive Board for Learning/Preparing. After you feel comfortable with the content you can prepare to present this talk in one of two ways.
- Project the Interactive Board for Presentation OR
- Reproduce a drawing of the differential diagnosis figure and timeline on a whiteboard.
The entire talk will take ~30-45 min.
- Slide 1: (5 min) Review the different components of an ABG and normal values by clicking on each of the "pH", "PCO2", etc buttons. Review the differences between "acidemia" and "acidosis" by click on the "emia vs osis" button.
- Slide 2: (2 min) Walk through the different steps in reading an ABG. Each blue button links to the respective page so do not click on any buttons until you are ready to move off this page. Emphasize that an anion-gap should be calculated for all cases regardless of the pH.
- Slide 3-4: (10-15 min) The next slides will walk you through the work-up and differential for acidemia, normal pH, alkalemia. We suggest going in this order: metabolic acidosis, respiratory acidosis, metabolic alkalosis, respiratory alkalosis, normal pH. While there is a lot of information to parse through, we suggest focusing on the steps rather than the specific differential.
- Slide 4: (5 min) We recommend spending time on the general principles of compensation rather than going through all of the different equations.
- Slide 5: (5 min) Quickly go through the basic practice cases just to solidify identifying the primary process. This should take less than 1 min per case.
- Slide 6-7: (10-20 min) Choose which cases you'd like to work through with your learners. Working through all of them may take up to 20 min.
Use for Self-Directed Learning and Preparing to Present
Use For Presenting (Less Text and Fewer Pop-ups)
TAKE HOME POINTS:
- There is a systematic way to read an ABG - look at the pH to identify the acid-base disturbance, then look at the HCO3 and PCO2 to identify the primary process and whether there is compensation.
- An AG should be calculated in all cases to identify if there is an underlying AGMA. When there is an AG, calculate the delta-delta to identify another concurrent metabolic process.
- HCO3 and PCO2 will move in the same direction for compensation. Respiratory compensation occurs quickly over hours. Metabolic compensation occurs more slowly over 2-3 days.