In the following flow diagram, Box A represents:
Metabolic alkalosis:
Metabolic alkalosis is characterised by an increase in the plasma bicarbonate concentration and the plasma pH. There is a compensatory rise in pCO2 due to hypoventilation, but this is limited by the need to avoid hypoxia. 
Classical causes include primary hyperaldosteronism (Conn’s syndrome), Cushing’s syndrome and glucocorticoid therapy. Occasionally, overuse of antacid salts for treatment of dyspepsia produces a similar pattern.
Metabolic alkalosis
Metabolic acidosis
Respiratory alkalosis
Respiratory acidosis