Causes of metabolic acidosis and their differential diagnosis
Metabolic acidosis is easiest classified as anion gap and non anion gap acidosis.
Anion gap is calculated as Na - (Cl + HCO3). If it is more than 12, it is abnormal and falls into the anion gap category.
Some conditions can cause a low anion gap to begin with e.g. Hypoalbuminemia, Lithium toxicity, IgG myeloma and some others that are not important (but all of these are either excess of positive ions or a lack of negative ions).
ANION GAP ACIDOSIS
Salicylate- also has respiratory alkalosis associated.
Lactate- can be due to many reasons e.g. infection, hypotension etc.
Uremia- Increased BUN/Cr, may have pericardial rub
Methanol- mediated through formic acid which causes blindness
Ethylene glycol- look for oxalate crystals in urine
DKA- type 1 diabetic or first time diagnosed young patient, urine dip will show ketones & glucose
NON - ANION GAP ACIDOSIS
Type1- Renal stones, distal type acidosis, hypokalemia, urine alwys alkalotic(>5.5)
Type2- No renal stones, Urine pH levels off and then becomes acidotic, Hypokalemia
Type3- Non existent (Category removed because found to be a type of type 2)
Type4- Hyperkalemia (associated with Diabetes, other states with hyporeninemic hypoaldosteronism)
Diarrhea- Low potassium too because it too is lost- also suspect a villous adenoma of colon.
Chloride infusion(NaCl)- In-patient setting.