Compensation: Restoring pH to normal
•Any primary disturbance immediately triggers a compensatory response.
Any respiratory disorder will be compensated for by the kidneys (process takes hours to days - 1 to 3 days).
Any metabolic disorder will be compensated for by the lungs (rapid process, occurs within minutes - 1 to 3 minutes).
Respiratory acidosis (hypoventilation)
Compensatory Response: Renal retention of HCO3– raises pH toward normal
Compensatory Response: Renal elimination of HCO3– lowers pH toward normal
Compensatory Response: Hyperventilation ↓CO2, raising pH toward normal
Compensatory Response: Hypoventilation ↑CO2, lowering pH toward normal
The CO2 hydration reaction's effect on [HCO3–]
A large portion of CO2 is transported as HCO3–. So any thing that affects CO2 will also affect HCO3– levels, yet this is not part of the renal compensatory response - only a result of the hydrolysis reaction. As such, slight changes in the HCO3– in the blood are an expected consequence of elevated or decreased PCO2 and should not be interpreted as compensatory.
As CO2 increases, it also increases HCO3–.
In general, the effect is an acute increase of ~1 mEq/L HCO3– for every 10 mm Hg acute increase in PaCO2 .
An increase in CO2 of 30 would increase HCO3– by ~3 mEq/L . This should not be seen as compensation.