PulmTools ABG Learning Hub
How to Interpret an ABG Step by Step
A simple, student-friendly guide to arterial blood gas interpretation with step-by-step logic, normal values, compensation clues, oxygenation review, and real clinical examples. Whether you are an RT student, nursing student, PA student, med student, or clinician who wants a faster bedside system, this page is built to help you learn the reasoning behind ABGs instead of just memorizing labels.
Start here: the fastest ABG interpretation framework
If you only remember one workflow, remember this one. This is the fastest way to go from raw numbers to a clinically useful answer.
- Check the pH first.
- Decide whether the primary disorder is respiratory or metabolic.
- Assess whether compensation is present and appropriate.
- Evaluate oxygenation with PaO₂ and, if needed, the P/F ratio or A–a gradient.
Which PulmTools ABG resource should you use?
Step-by-step guide
Best if you are still learning the logic and want a structured explanation of pH, PaCO₂, HCO₃⁻, compensation, and oxygenation.
ABG Analyzer
Best for bedside use when you already have a blood gas and want a fast interpretation with less mental math.
ABGenius
Best for building speed and retention with repeated case exposure, instant feedback, and realistic ABG pattern recognition.
Step-by-Step ABG Interpretation
1. Look at pH
Determine if the patient is acidemic (< 7.35) or alkalemic (> 7.45). This is the anchor for the rest of the interpretation.
2. Check PaCO₂
PaCO₂ reflects respiratory status. High PaCO₂ points toward respiratory acidosis. Low PaCO₂ points toward respiratory alkalosis.
3. Evaluate HCO₃⁻
HCO₃⁻ reflects metabolic status. Low bicarbonate suggests metabolic acidosis. High bicarbonate suggests metabolic alkalosis.
4. Determine Compensation
Check whether the body is compensating appropriately. For metabolic acidosis, use tools like Winter’s Formula. If compensation does not fit, think mixed disorder.
5. Assess Oxygenation
Look at PaO₂ and consider the P/F ratio or A–a gradient when oxygenation needs deeper analysis.
Normal ABG Values
- pH: 7.35 – 7.45
- PaCO₂: 35 – 45 mmHg
- HCO₃⁻: 22 – 26 mEq/L
- PaO₂: 80 – 100 mmHg
Worked ABG examples
Example 1
7.25 / 60 / 26 / 55
pH is low, PaCO₂ is high, and bicarbonate is still near normal. This fits acute respiratory acidosis with moderate hypoxemia.
Example 2
7.30 / 20 / 10 / 92
pH is low, bicarbonate is low, and PaCO₂ is also low in the compensatory direction. This fits partially compensated metabolic acidosis with normal oxygenation.
Example 3
7.48 / 32 / 24 / 88
pH is high and PaCO₂ is low, pointing toward respiratory alkalosis. This is a common ABG pattern to see in anxiety, pain, or early hypoxemic states.
Use the right CTA for your goal
Need to learn?
Use ABGenius if you want repeated practice cases, active recall, and faster pattern recognition.
Practice with ABGeniusNeed to analyze a real ABG?
Use the ABG Analyzer if you already have values and want a fast interpretation for bedside use.
Open ABG AnalyzerInternal links that help you go deeper
If you want to move beyond basic ABG interpretation, these guides will tighten up your reasoning around compensation, oxygenation, and mixed disorders.