Metabolic Acidosis part I

Metabolic Acidosis (limited mostly to increased AG metabolic acidosis and delta-delta

Check anion gap
If anion gap increased --> suggests increased unmeasured anions: organic acids, phosphates, sulfates
If anion gap decreased --> suggests decreased albumin or increased unmeasured cations: Ca, Mg, K, Li, bromine, immunoglobulins

If increased AG, determine the delta-delta (or delta ratio) to assess for other concomitant metabolic abnormalities.

Delta-delta = (delta anion gap)/(delta HCO3)
Delta anion gap = Calculated anion gap - Expected anion gap
Calculated anion gap = Na - (Cl - HCO3)
Expected anion gap = Albumin x 2.5
Delta HCO3 = 24 - HCO3

If delta-delta value:
1-2 --> pure AG metabolic acidosis
<1 --> AG metabolic acidosis and concomitant non-gap metabolic acidosis
>2 --> AG metabolic acidosis and concomitant metabolic alkalosis

Aids for intuition:
If delta ratio > 2, this points to a relatively small delta HCO3 (as the denominator will be relatively small).
If delta ratio < 1, this points to a relatively large delta HCO3 (relative to delta AG).  Increased Cl can account for this.


Osmolal Gap = Measured osmolality - calculated osmolality
Calculated osmolality = (Na x 2) + (glucose/18) + (BUN/2.8)
If osmolal gap > 10, suggests ingestion