# 6.5: Compensation

- Page ID
- 10902

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## The compensatory response is a fall in bicarbonate level

As can be seen by inspection of the Henderson-Hasselbalch equation (below), a decreased [HCO3^{ -}] will counteract the effect of a decreased pCO2 on the pH. Mathematically, it returns the value of the \( \frac {[HCO_{3}^{-}]} {0.03pCO_{2}} \) ratio towards normal.

**\[ pH = pKa + \log \frac {[HCO_{3}^{-}]} {0.03pCO_{2}} \]**

## Key points regarding compensation in respiratory alkalosis:

- Physicochemical effect: Initially there is an immediate physicochemical change which lowers the bicarbonate slightly.
- Role of Kidney: The effector organ for compensation is the kidney.
- Slow Response: The renal response has a slow onset and the maximal response takes 2 to 3 days to be achieved.
- Outcome: The drop in bicarbonate results in the extracellular pH returning only
*partially*towards its normal value.