Fig. 36.1 Diagnosis of acid–base disorders (This figure was published in Miller textbook, Chap. 21 in 2011. Permission obtained from Elsevier to reproduce the image.)
- 3.
Anion gap (AG) = Na − (Cl + HCO3)
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AG is the difference in the ‘routinely measured’ cations (Na) and ‘routinely measured’ anions (Cl and HCO3) in the blood and depends on serum phosphate and albumin concentrations [2]. Determination of AG is useful in determining the cause of acidosis [3, 4]. The normal value for serum AG is usually 8–12 mEq/L. In our patient, AG = 130 − (80 + 10) = 40 mEq/L. So, this patient has a high AG, most likely due to starvation or diabetic ketoacidosis.
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In a normal healthy patient, negatively charged albumin is the single largest contributor to the AG [5]. Hypoalbuminemia causes a decrease in AG; hence AG is corrected to albumin level using the equation of Figge as follows: corrected AG = AG + [0.25 × (44 – Albumin)] [6].
If corrected AG >16, there is high AG acidosis.
If corrected AG <16, non-AG acidosis.
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- 4.
Delta gap formula can be used to assess mixed acid–base disorder.
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Δ gap = AG − 12 + HCO3 (12 is normal serum AG value)
If Δ gap <22 mEq/L, then concurrent non-gap metabolic acidosis exists.
If Δ gap >26 mEq/L, then concurrent metabolic alkalosis exists.
- (b)
In our patient, Δ gap = 40 − 12 + 10 = 38 mEq/L. So, there is a concurrent metabolic alkalosis probably from vomiting in addition to high AG metabolic acidosis in this patient.
So, there is a concurrent metabolic alkalosis probably from vomiting in addition to high AG metabolic acidosis in this patient.
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- 5.
Winter’s formula is used to determine whether there is an appropriate respiratory compensation during metabolic acidosis [1].
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- (a)
Winter’s formula: PCO2 = (1.5 × HCO3) + 8
If measured PCO2 > calculated PCO2, then concurrent respiratory acidosis is present.Related posts:
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