Compensatory mechanism in metabolic acidosis:

The buffer system mainly bicarbonate/carbonic acid minimizes the changes in pH. In acidosis the bicarbonate concentration decreases to give a ratio of <20:1. The respiratory compensatory mechanism is by hyperventilation.

Respiratory compensation mechanism:

The decrease in pH stimulates respiratory compensatory mechanism and produces hyperventilation (Kussmaul respiration), which results in elimination of carbonic acid as carbondioxide, a decrease in pCO₂ and decrease in cdCO₂. As cdCO₂ diminishes, the ratio of cHCO₃/cdCO₃ returns to normal 20:1.

Renal compensatory mechanism:

There is increase excretion of acid and preservation of base (increased rate of Na-H exchange, increased ammonia formation, and increased reabsorption of bicarbonate). This results in increase in ratio. 22:1.1 for pH of 7.40 (fully compensated metabolic acidosis as pH is normal).