Identify the "Culprit"! Uncovering the True Nature of Acidosis with Anion Gap
YouTube https://youtu.be/2Ef4C7GKoek
"Blood gas analysis is difficult and I'm not good at it..."
Young nurses and residents who feel this way, please gather around.
When you look at blood gas analysis results, do you just stop at "It's acidosis!" because the pH is low?
If so, you might be missing "what is happening in the patient's body (= the culprit)."
Today, let's master the ultimate weapon essential for "finding the culprit" in blood gas: the Anion Gap (AG).
🕵️♂️ First, distinguish between "emia" and "osis"
If you confuse these, you will look unprofessional in conversations with senior doctors.
Acidemia: The "state" where blood pH is less than 7.35
Acidosis: The "process" of trying to lower the pH (the culprit's work)
What we need to look for is the "culprit (acidosis)" that is trying to turn the blood acidic.
🗑️ There are "two types" of acidosis
Metabolic acidosis can be broadly divided into two types. Think of it like a "trash can."
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Type where Anion Gap (AG) increases:
A state where "acid (trash)" is accumulating in the body, causing the trash can to overflow.
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Type where Anion Gap (AG) is normal:
A state where "alkali (trash bags)" is leaking out of the body, making acid relatively dominant.
The indicator to determine whether "trash (acid) has accumulated" or "bags (alkali) have leaked" is the Anion Gap (AG).
🧮 The "AG formula" to corner the culprit
To be able to calculate it quickly in the field, please engrave this formula into your brain.
Reference range: 12±2 (10-14)
If this value exceeds 14, you can conclude that 'abnormal acid that shouldn't be there' is accumulating in the body, which means it is an 'AG-elevated (increased) metabolic acidosis'.
💡 [Note Exclusive] Professional Perspective: Don't Forget Albumin Correction!
From here on, this is the step up to 'expert' level that couldn't be fully covered in the video.
In fact, the AG value is greatly influenced by 'albumin'. Since albumin carries an anion (negative charge), in patients with hypoalbuminemia, even if acid is actually accumulating, the calculated AG may appear low, creating a risk of 'missing the culprit'.
When examining patients with poor nutritional status or critically ill patients, be sure to use this corrected AG.
Example: For a person with an albumin of 2.0 g/dL
🚨 These are the '3 Main Culprits' that raise AG!
If the AG is elevated, suspect these three. The mnemonic is 'K-U-L'.
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K: Ketoacidosis
Such as Diabetic Ketoacidosis (DKA).
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U: Uremia
A state where acids that should be excreted are accumulating due to renal failure.
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L: Lactic Acidosis
A state where lactic acid has exploded due to shock or tissue ischemia.
📝 Summary: Blood Gas is 'Deduction'
pH Check: Is there acidemia?
AG Calculation: Calculate Na - (Cl + HCO3).
Albumin correction: If albumin is low, add to the value.
Identify the culprit: If AG > 14, suspect "K-U-L"!
Blood gas results are not just a string of numbers. They are the "evidence" of the incident occurring within the patient's body.
Just by adopting this perspective, your level of clinical reasoning will improve significantly.
Thank you for reading until the end!
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For those who want to learn more in detail, please check out this explanatory video as well.