use delta delta gap to calculate third acid base disorder

• related: Nephrology
• tags: #permanent

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2 ways to calculate delta delta. You can use delta gap or delta ratio.

Delta Gap

1. calculate the anion gap(AG).
2. calculate the delta anion gap.
3. add the delta anion gap to the current HCO3–.
   • sum < 22: additional non-anion gap metabolic acidosis
   • sum > 26: additional metabolic alkalosis occurring¹²

Example

This patient has a high anion gap metabolic acidosis. Her sodium level is 152 mEq/L (152 mmol/L), and her anion gap is 28, or 18 above the normal anion gap of 10. If one adds that 18 back to the bicarbonate value of 8, the sum is 26, suggesting that she may have a slight metabolic alkalosis but does not have a normal anion gap metabolic acidosis in addition to her high anion gap metabolic acidosis.

Delta Ratio

$\Delta\Delta\space ratio = \frac{AG-12}{24-\space bicarb}$

• <0.4: NAGMA. Top number is very small.
• 0.4-0.8: AGMA with NAGMA. Top number slightly higher. Maybe some underlying AGMA.
• 1-2: AGMA

• 2: AGMA with preexisting elevated bicarb. Bottom number very small, meaning chronic elevated bicarb either from chronic hypercapnia with metabolic compensation or chronic metabolic alkalosis (e.g. diuresis)

Links to this note

• Nephrology

  • use delta delta gap to calculate third acid base disorder

• anion gap metabolic acidosis

  • use delta delta gap to calculate third acid base disorder

Footnotes

1. Mehta AN, Emmett JB, Emmett M. GOLD MARK: an anion gap mnemonic for the 21st century. Lancet. 2008;372(9642):892. PubMed ↩

2. Palmer BF, Clegg DJ. Hyperchloremic normal gap metabolic acidosis. Minerva Endocrinol. 2019;44(4):363-377. PubMed ↩