ABG Interpreter — Acid–Base Analyzer
Interpret an arterial blood gas in seconds. Enter pH, pCO₂ and HCO₃⁻ to identify the primary acid–base disorder, judge whether compensation is appropriate, and (with sodium and chloride) calculate the anion gap.
Blood gas values
Electrolytes (optional — for anion gap)
Normal: pH 7.35–7.45 · pCO₂ 35–45 mmHg · HCO₃⁻ 22–26 mmol/L.
For education/reference only — not a substitute for clinical judgment. Uses Winter’s formula for expected respiratory compensation. Calculated locally in your browser.
The 4-step approach
- Look at the pH — is the patient acidotic or alkalotic?
- Is the primary problem respiratory (pCO₂) or metabolic (HCO₃⁻)?
- Is there appropriate compensation?
- Calculate the anion gap to characterise a metabolic acidosis.
Frequently asked questions
How do you interpret an ABG step by step?+
First check the pH (acidosis < 7.35, alkalosis > 7.45). Then decide whether the primary driver is respiratory (pCO₂) or metabolic (HCO₃⁻). Finally assess whether compensation is appropriate and calculate the anion gap. This tool does all four steps automatically.
What is Winter’s formula?+
For a metabolic acidosis, the expected pCO₂ = 1.5 × HCO₃⁻ + 8 (± 2 mmHg). If the measured pCO₂ falls in that range, respiratory compensation is appropriate; outside it suggests an additional respiratory disorder.
How is the anion gap calculated?+
Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻). A value above ~12 mmol/L is high and, in an acidotic patient, points to a high-anion-gap metabolic acidosis. Enter sodium and chloride to include it.
What are the normal ABG values?+
pH 7.35–7.45, pCO₂ 35–45 mmHg, HCO₃⁻ 22–26 mmol/L.
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