What is the first step in ABG interpretation?

The first step is to look at the pH to determine whether the patient is acidemic or alkalemic.

What are normal ABG values?

Typical normal ABG values are pH 7.35 to 7.45, PaCO2 35 to 45 mmHg, HCO3 22 to 26 mEq/L, and PaO2 80 to 100 mmHg.

PaCO2 reflects the respiratory component and HCO3 reflects the metabolic component. Comparing each to the pH helps identify the primary disorder.

Winter's formula is used to predict the expected PaCO2 in metabolic acidosis so you can assess whether respiratory compensation is appropriate.

Oxygenation helps you evaluate how well the lungs are moving oxygen into the blood. PaO2, PF ratio, and the A-a gradient can all help assess this.

A simple, student-friendly guide to arterial blood gas (ABG) interpretation with step-by-step logic, normal values, and clinical examples.

Determine if the patient is acidemic (< 7.35) or alkalemic (> 7.45).

PaCO₂ reflects respiratory status. High = respiratory acidosis. Low = respiratory alkalosis.

HCO₃⁻ reflects metabolic status. Low = metabolic acidosis. High = metabolic alkalosis.

Check if the body is compensating appropriately. Use formulas like Winter’s formula for metabolic acidosis.

Look at PaO₂ and consider PF ratio or A–a gradient if needed.

Practice interpreting ABGs with our interactive calculator.