Metabolic acidosis

Background

• Primary acidosis if pH <7.38
• HCO3 <24 = metabolic acidosis
• Always determine if there is another acid/base process occurring
  • Primary respiratory acidosis if pCO2 > pCO2expected
  • Primary respiratory alkalosis if pCO2 < pCO2expected
    • use Winter's formula: PCO2 (expected) = (1.5 x [HCO3–] + 8) ± 2
    • In acute setting PCO2 should fall by 1 mmHg for every 1 mEq fall in HCO3
  • Concurrent metabolic alkalosis if delta-delta > 28
  • Delta-Delta = (AG - 12) + HCO3

DDX

Gap

1. Lactic acidosis
   1. Sepsis, shock, liver dz, CO, CN, metformin, methemoglobin
2. Renal failure
   1. Uremia
3. Ketoacidosis
   1. DKA, AKA, starvation
4. Ingestions
   1. Inc osm gap
      1. Methanol, ethylene glycol
   2. Normal osm gap
      1. ASA, iron, INH
   3. Osm gap = measured osm - calculated osm (normal 10-15)
   4. Calculated Osm = 2(Na)+(glucose/18)+(BUN/2.8)+(BAL/5)

Non-gap

1. Hyperkalemia
   1. Resolving DKA
   2. Early uremic acidosis
   3. Early obstructive uropathy
   4. RTA Type IV
   5. Hypoaldo
   6. K-sparing diuretics
2. Hypokalemia
   1. RTA Type I
   2. RTA Type II
   3. Acetazolamide
   4. Acute diarrhea
      1. (May be assoc with gap if hypoperfusion -> lactic acidosis)

Treatment

1. Treat source
2. Correct any respiratory acidosis
3. Bicarbonate
   1. HCO3 dose in mEq = 0.5(wt in kg) x (24 - measured HCO3)
   2. Each bicarb 0.5mEq/kg causes 1 meq/L rise in HCO3
   3. Consider for:
      1. Bicarb <4
      2. pH <7.20 AND shock/myocardial irritability
      3. Severe hyperchloremic acidemia
      4. lower threshold with non-AG acidosis (greater HCO3 loss)
         1. Lost bicarbonate would take days to replenish

Source

Tintinalli