Acid-Base Balance Types

Overview

This lecture explains the differences between full, partial, and uncompensated states in acid-base balance, with a focus on interpreting lab values.

Full compensation occurs when pH is within the normal range (7.35–7.45).
Compensation means one organ corrects for another that is in trouble (e.g., kidneys help lungs or vice versa).
If respiratory acidosis is present and pH normalizes, the kidneys have fully compensated by adjusting bicarbonate (HCO3).
Similarly, if metabolic alkalosis is present and pH normalizes, the lungs have fully compensated by adjusting CO2 levels.

Partial compensation is when the compensating organ is helping, but pH is still abnormal (not 7.35–7.45).
For respiratory acidosis, if bicarbonate is elevated (>26) but pH is still <7.35, kidneys are partially compensating.
For metabolic alkalosis, if CO2 is elevated (>45) but pH is still >7.45, lungs are partially compensating.
Compensation is shown by the movement of the compensating value (HCO3 or CO2) out of its normal range while pH remains abnormal.

To determine compensation, always check the pH first.
If pH is normal, there is full compensation; if not, look for changes in compensating values to determine partial compensation.
The degree of compensation is judged by how close the pH is to normal and if compensating values are outside their normal range.

Compensation — The process by which one organ system attempts to correct acid-base imbalances caused by another.
Full compensation — pH is normal (7.35–7.45) and the compensating organ's values are outside normal.
Partial compensation — Compensating organ's values are outside normal, but pH is still abnormal.
Uncompensated — No compensation has occurred; compensating organ's values remain normal.
Bicarbonate (HCO3) — A base controlled by the kidneys (normal: 22–26).
CO2 (Carbon dioxide) — An acid controlled by the lungs (normal: 35–45).