Respiratory Compensations for Acid-Base Abnormalities Occur Rapidly; Renal Compensations Occur over Several Hours
This discussion of acid-base disturbances shows that the lungs compensate for metabolic problems, and the kidneys compensate for respiratory problems. Because the ehemoreceptors respond almost immediately to changes in blood pH, and because changes in ventilation rapidly change Pco2, respiratory compensation for metabolic acid-base problems occurs almost immediately.
For this reason, it is rare to observe “pure” metabolic acidosis or alkalosis without a respiratory compensation. The response of the kidneys to a respiratory acid-base disturbance is less rapid, and changes in NH3 and HCO3" production occur over about 24 hours.As compensatory mechanisms adjust the pH toward normal, there is less “error signal” to drive the compensation; thus these mechanisms alone rarely return the pH to normal. In metabolic acidosis, for example, the low pH drives ventilation to decrease Pco2. As the pH returns to normal, however, the respiratory drive to compensate is reduced; therefore, restoration of normal pH is rarely complete.