How do you tell acute from chronic respiratory acidosis?

You compare the bicarbonate level to the expected compensation. In acute respiratory acidosis, HCO3 rises about 1 mEq/L for every 10 mmHg increase in PaCO2. In chronic respiratory acidosis, HCO3 rises about 3 to 4 mEq/L for every 10 mmHg increase in PaCO2.

How do you tell acute from chronic respiratory alkalosis?

You compare the bicarbonate level to the expected compensation. In acute respiratory alkalosis, HCO3 falls about 2 mEq/L for every 10 mmHg decrease in PaCO2. In chronic respiratory alkalosis, HCO3 falls about 4 to 5 mEq/L for every 10 mmHg decrease in PaCO2.

Why is respiratory compensation important in ABG interpretation?

Respiratory compensation rules help determine whether the kidneys are responding appropriately to a primary respiratory disorder and whether a mixed acid-base disorder may also be present.

Can abnormal compensation suggest a mixed disorder?

Yes. If the bicarbonate change does not match expected acute or chronic compensation rules, there may be an additional metabolic or respiratory acid-base disorder present.

ABG Compensation & Acid-Base

Respiratory Compensation Explained (Acute vs Chronic)

2026-03-24 · ~8 min read

ABG Interpretation Guide Winter's Formula Mixed Disorders Guide

Respiratory compensation is one of the most important concepts in ABG interpretation. It tells you whether the kidneys are responding appropriately to changes in CO₂ — and more importantly, whether a mixed acid-base disorder is present.

This page connects directly with the ABG Interpretation Guide, Winter's Formula, and Mixed Acid-Base Disorders.

Compensation Rules (High-Yield Tables)

Respiratory Acidosis

Type	PaCO₂ Change	HCO₃⁻ Change
Acute	+10	+1
Chronic	+10	+3–4

Respiratory Alkalosis

Type	PaCO₂ Change	HCO₃⁻ Change
Acute	-10	-2
Chronic	-10	-4–5

Acute vs Chronic: Why It Matters

The difference between acute and chronic respiratory disorders comes down to time.

Acute: kidneys haven't had time to compensate
Chronic: kidneys retain or excrete bicarbonate

How to Use This on an ABG

Identify primary disorder
Check expected compensation
Compare to actual HCO₃⁻
Decide if mixed disorder exists

This step is critical when working through a full ABG interpretation or identifying mixed disorders.

Worked Example

ABG: pH 7.30 / PaCO₂ 60 / HCO₃⁻ 26

CO₂ is elevated → respiratory acidosis. Expected acute compensation = +2 HCO₃⁻. This fits → acute respiratory acidosis.