Enter arterial blood gas values
Example data table
| Scenario | pH | PaCO2 | HCO3 | PaO2 | FiO2 | Likely reading |
|---|---|---|---|---|---|---|
| Reference pattern | 7.40 | 40 | 24 | 95 | 21% | Balanced acid-base state |
| DKA-type pattern | 7.22 | 24 | 10 | 88 | 21% | High-gap metabolic acidosis with compensation |
| COPD retention pattern | 7.33 | 60 | 31 | 58 | 28% | Chronic respiratory acidosis with hypoxemia |
| Vomiting pattern | 7.50 | 48 | 36 | 90 | 21% | Metabolic alkalosis with respiratory compensation |
Formula used
- Henderson-Hasselbalch: pH = 6.1 + log10(HCO3 / (0.03 x PaCO2)).
- Anion gap: AG = Sodium - (Chloride + Bicarbonate).
- Albumin-corrected anion gap: Corrected AG = AG + 2.5 x (4.0 - Albumin).
- Winter's compensation: Expected PaCO2 = 1.5 x HCO3 + 8, with a plus or minus 2 range.
- Metabolic alkalosis compensation: Expected PaCO2 = 0.7 x (HCO3 - 24) + 40, with a plus or minus 5 range.
- Respiratory acidosis compensation: Acute HCO3 rises about 1 per 10 mmHg PaCO2. Chronic HCO3 rises about 3.5 per 10 mmHg.
- Respiratory alkalosis compensation: Acute HCO3 falls about 2 per 10 mmHg PaCO2. Chronic HCO3 falls about 5 per 10 mmHg.
- Alveolar gas equation: PAO2 = FiO2 x (Patm - 47) - (PaCO2 / RQ).
- A-a gradient: A-a gradient = PAO2 - PaO2.
- P/F ratio: P/F ratio = PaO2 / FiO2 fraction.
How to use this calculator
- Enter the measured pH, PaCO2, HCO3, and PaO2 values from the arterial sample.
- Enter FiO2 as a percentage. Use 21 for room air.
- Add sodium, chloride, and albumin to calculate anion gap and albumin correction.
- Enter age to compare the measured A-a gradient with an estimated normal value.
- Adjust atmospheric pressure and respiratory quotient when altitude or special physiology matters.
- Click Calculate ABG to show the result above the form.
- Review the primary interpretation, compensation check, oxygenation metrics, and chart together.
- Use the CSV and PDF buttons to save the calculated summary.
Frequently asked questions
-
What does this calculator identify first?
It starts with acidemia, alkalemia, or near-reference pH. Then it compares PaCO2 and HCO3 to estimate the dominant primary disorder and likely compensation pattern. -
Why is albumin included?
Low albumin lowers the apparent anion gap. Correcting for albumin can reveal a hidden high-gap metabolic acidosis that the raw anion gap may underestimate. -
What is the benefit of the A-a gradient?
The A-a gradient helps separate hypoventilation from gas-exchange problems. A higher gradient suggests diffusion, ventilation-perfusion mismatch, or shunt physiology. -
Why does the calculator show calculated pH too?
The calculated pH cross-checks internal consistency between bicarbonate and carbon dioxide. A larger gap from measured pH may suggest rounding, transcription, or measurement issues. -
Can this detect mixed disorders?
Yes. It compares measured values with expected compensation ranges. When numbers fall outside those ranges, the output flags possible concurrent respiratory or metabolic processes. -
What does delta ratio mean here?
Delta ratio helps interpret high anion gap metabolic acidosis. It can suggest a pure high-gap process, an added normal-gap acidosis, or a concurrent metabolic alkalosis. -
Should I use local reference ranges?
Yes. Laboratories and clinical settings may use slightly different normal values. This calculator offers structured guidance, but the final interpretation should match local standards. -
Is this suitable for emergency decisions alone?
No. It is a decision-support tool for education and review. Patient symptoms, vital signs, chemistry panels, lactate, and clinician judgment remain essential.