ABG Calculator
Interpret arterial blood gas results, identify acid-base disorders, and assess respiratory or metabolic compensation using pH, PaCO₂, HCO₃⁻, and oxygenation values.
How to Use the ABG Calculator
Enter core arterial blood gas values to identify the primary acid-base disorder, review expected compensation, and screen oxygenation or metabolic markers when available. Refer to the clinical guide on arterial blood gas interpretation for systematic analysis.
Enter pH, PaCO2, and HCO3 from the arterial blood gas report.
Choose acute or chronic mode when a respiratory disorder is suspected.
Add sodium and chloride if you want an anion gap check.
Use the advanced tab for PaO2, FiO2, albumin, lactate, age, and temperature.
Review the primary disorder, compensation status, and any mixed-disorder flags.
Use the simulator to model how ventilation and bicarbonate shifts affect pH.
Why Interpret ABGs Systematically?
ABG interpretation is easiest to audit when the same sequence is followed every time: pH first, then respiratory and metabolic drivers, then compensation and oxygenation.
- Fewer missed mixed disorders: Compare measured values against expected compensation.
- Better oxygenation context: Add A-a gradient and P/F ratio when PaO2 and FiO2 are known.
ABG Interpretation Formulas
The calculator combines acid-base classification with compensation checks, anion gap logic, and oxygenation formulas. Learn more about acid-base compensation formulas used to evaluate simple and mixed disorders.
Classify pH
pH below 7.35 is acidemia; pH above 7.45 is alkalemia.
Find the Primary Driver
PaCO2 points to respiratory change; HCO3 points to metabolic change.
Check Compensation
Expected compensation formulas help reveal whether a second primary disorder is present.
Add Oxygenation Context
Use PaO2 and FiO2 for A-a gradient and P/F ratio when oxygenation matters.
ABG Example Interpretation
Suppose an ABG shows pH 7.28, PaCO2 55 mmHg, and HCO3 26 mEq/L. The low pH and high PaCO2 point toward respiratory acidosis.
Common ABG Reference Ranges
Use local laboratory ranges and clinical context to classify simple and mixed acid-base disorders.
| Parameter | Typical Range | Main Signal |
|---|---|---|
| pH | 7.35 - 7.45 | Acid-base state |
| PaCO2 | 35 - 45 mmHg | Respiratory |
| HCO3 | 22 - 26 mEq/L | Metabolic |
| PaO2 | 80 - 100 mmHg | Oxygenation |
| SaO2 | 95% - 100% | Oxygen saturation |
Clinical Interpretation Checks
ABG values should be interpreted with patient history, symptoms, oxygen delivery, altitude, sample quality, and local reference ranges.
Clinical Note
Use the calculator as decision support, not as a substitute for bedside assessment or medical judgment.
Mixed Disorder Signals
Mixed acid-base disorders become more likely when the measured compensatory response falls outside the expected range, the anion gap is elevated, or oxygenation results do not match the clinical picture. Consult the guidelines on anion gap interpretation to evaluate metabolic acidosis.
ABG Calculator FAQ
Essential answers for arterial blood gas interpretation and compensation checks.
What does an ABG calculator do?
It interprets pH, PaCO2, and HCO3 values to identify acidosis or alkalosis, determine the likely primary system, and estimate whether compensation is appropriate.
What are normal ABG values?
Common adult reference ranges are pH 7.35-7.45, PaCO2 35-45 mmHg, HCO3 22-26 mEq/L, PaO2 80-100 mmHg, and SaO2 95-100%.
Why is Winter's formula important?
Winter's formula estimates expected PaCO2 in metabolic acidosis. A measured PaCO2 above or below the expected range can suggest an additional respiratory disorder.
When should I use corrected anion gap?
Use corrected anion gap when albumin is low, because hypoalbuminemia can make the measured anion gap look falsely normal.
What is the A-a gradient used for?
The A-a gradient (or alveolar-arterial oxygen gradient) helps separate hypoxemia caused by lung gas-exchange problems from hypoxemia due to hypoventilation or low inspired oxygen.
Can this replace clinical judgment?
No. It is an educational and decision-support tool. ABG interpretation must be combined with patient history, examination, treatment context, and local lab standards.
Clinical reference notes
Equations and ranges should be confirmed against local protocols.
References include NCBI Bookshelf clinical reviews on arterial blood gas interpretation and Merck Manual Professional guidance on acid-base disorders and compensation. This calculator is for educational and clinical decision-support use only and does not replace independent medical judgment.