ii. Root causes
      a. Upper GI H+ losses (vomiting or NG suction)
      b. Renal H+ losses (e.g. diuretics, hyperaldo)
         1. Diuretics ("contraction"); actually, diuretics probably
            cause metabolic alkalosis by mechanisms described under
            "pathopysiology" rather than by contraction around the HCO3-
         2. Primary mineralocorticoid excess
         3.  K+ (severe) with  GFR
      c. Colonic H+ losses (diarrhea or villous adenoma or laxative
         abuse with secondary renal dysfunction?)
      d. Alkali ingestion (IV or PO bicarb or CaCO3) (rare)
      e. Posthypercapnic: after CO2 normalized, takes a while for the
         compensatory  HCO3- to normalize.
      f. Hypoparathyroidism:  PTH causes HCO3- excretion, lack >
         retention.