AG = Na - (Cl + HCO3)
Normal AG = 10 - 12 mEq/L
Normal anion gap (AG) = serum albumin x 3.
High AG >10-12. mEq/L.
Low AG gap - causes:
Hypoalbuminemia (normal AG is largely accounted for anionic plasma proteins - albumin)
Halide (Br- or I-) intoxication
Severe hyperlipidemia
Multiple myeloma (cationic IgG paraproteins)
Anion Gap Metabolic Acidosis:
MUDPILES:
Methanol, metformin, uremia, DKA, paraldehyde, INH, iron tablets, lactic acidosis, ethanol, ethylene glycol, salicylates, rhabdomyolysis
Check presence or absence of ketonuria:
Ketonuria: DKA, EtOH, paraldehyde poisoning, starvation, isopropyl alcohol intoxication (does not cause acidosis)
No ketonuria: uremia, lactic acidosis, methanol
Normal Anion Gap Metabolic Acidosis:
RTA types 1, 2, and 4
Renal HCO3- loss/RTA2
▼ H+ secretion/RTA1
Hypoaldosterone related/RTA4
Nonrenal HCO3- loss in diarrhea, pancreatic fistula, biliary, urinary diversion, ileostomy.
Cholestyramine, or ingestion of Ca and Mg chloride
Rapid infusion of NS
Spironolactone, TMP, ACE-I, pentamidine, NSAIDs, cyclosporine, acetazolamide (CI inhibitors),beta blockers
Tx:
Treat the underlying cause
Severe acidosis (pH <7.2) may require treatment with parenteral NaHCO3.
Bicarbonate deficit may be calculated as follows:
HCO3 deficit in mEq/L = 0.5 x body wt in kg - (24 - measured HCO3).
Rapid infusion of sodium bicarbonate should be considered for only severe acidosis.
Overaggressive correction should be avoided to prevent overshoot alkalosis.
Hypernatremia and fluid overload can occur with NaHCO3 administration.
Serum electrolytes should be followed closely
Bicarbonate
1 ampoule of 8.4% NaHCO3 = 50 mEq NaHCO3 = 1000 mEq Na/L
Give in D5W.
To give HCO3- in acute setting:
HCO3- deficit = 0.5 x body wt in Kg (24 - HCO3 measured). Keep the HCO3 desired 15 mEq/L.
0.5 x body wt in kg (15 - bicarb measured).
Give 1/2 the dose slowly.
D5W + Sodium bicarbonate is generally the fluid of choice in Pts who are oliguric, hyperkalemic, and acidotic.