Rex says
Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.
Try a scenario
Click to load — tweak from there.Inputs
Result
Likely primary disorder
Primary metabolic acidosis
Expected pCO2 (Winter's formula)
29.0
Compensation assessment
Appropriate respiratory compensation
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How to use this
- 1Enter ph.
- 2Enter pco2 (mmHg).
- 3Enter bicarbonate (hco3) (mEq/L).
- 4Read your likely primary disorder on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
Interpreting an arterial blood gas systematically avoids missing mixed disorders. This tool applies the standard sequence: check pH for acidemia or alkalemia, check pCO2 and HCO3 to see which is driving the primary disturbance, then apply Winter's formula to check whether respiratory compensation for a metabolic acidosis is appropriate, inadequate, or excessive (suggesting a second, superimposed process). It also flags likely primary respiratory acidosis or alkalosis based on pCO2 direction relative to pH. This is a structured educational aid, not a replacement for full clinical correlation — the same numbers can represent very different underlying physiology depending on history (renal failure, diabetic ketoacidosis, opioid overdose, sepsis, salicylate toxicity, and more all produce distinct but sometimes overlapping ABG patterns). Anion gap, lactate, and the clinical context are essential companions to this reading, and any ambiguous or mixed pattern should go to a clinician for full interpretation. This tool is for education and workflow support only — not medical advice. Always verify results with a clinician and use clinical judgment alongside your institution's protocols.
Worked example
Using the values the calculator loads with:
Inputs
- pH: 7.28
- pCO2: 30 mmHg
- Bicarbonate (HCO3): 14 mEq/L
Results
- Likely primary disorder: Primary metabolic acidosis
- Expected pCO2 (Winter's formula): 29
- Compensation assessment: Appropriate respiratory compensation
What each field means
Inputs
- pH
- The ph used in the calculation. Starts at 7.28 so you have a working example on load. Accepted range: 6.6–7.8.
- pCO2 (mmHg)
- The pco2 used in the calculation, measured in mmHg. Starts at 30 mmHg so you have a working example on load. Accepted range: 10–100 mmHg.
- Bicarbonate (HCO3) (mEq/L)
- The bicarbonate (hco3) used in the calculation, measured in mEq/L. Starts at 14 mEq/L so you have a working example on load. Accepted range: 2–45 mEq/L.
Results
- Likely primary disorder
- Returned as a plain value and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Expected pCO2 (Winter's formula)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Compensation assessment
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
What's the standard order to read an ABG?
Check pH first to establish acidemia versus alkalemia, then look at pCO2 and HCO3 to see which one moved in the direction that would explain the pH — that's your primary process. Then check whether the other value moved in the expected compensatory direction and by the expected amount, using formulas like Winter's for metabolic acidosis.
What does it mean if compensation is 'better' or 'worse' than expected?
If the actual pCO2 is lower than Winter's formula predicts, there's likely an additional primary respiratory alkalosis on top of the metabolic acidosis (common in sepsis or salicylate toxicity). If pCO2 is higher than predicted, there's likely a superimposed respiratory acidosis, meaning the patient cannot compensate adequately, often due to fatigue or a separate lung process.
Should I calculate anion gap too?
Yes, always, alongside this tool. Anion gap tells you whether a metabolic acidosis is due to unmeasured acids (ketoacidosis, lactic acidosis, toxic alcohols, renal failure) versus a non-gap process (diarrhea, renal tubular acidosis, saline-induced). This ABG aid does not calculate anion gap — pair it with a dedicated anion gap tool.
Can this replace a clinician's interpretation?
No. This structured walkthrough teaches the pattern-recognition steps, but real patients frequently have mixed or evolving disorders that require full clinical context, trend over time, and lab correlation (lactate, ketones, toxicology) that a single ABG snapshot cannot capture.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). ABG Interpretation Aid. Retrieved from https://www.revenuelab.fyi/toolbox/abg-interpretation
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/abg-interpretation" target="_blank" rel="noopener">ABG Interpretation Aid — RevenueLab</a> (2026).</p>
Source: [ABG Interpretation Aid — RevenueLab](https://www.revenuelab.fyi/toolbox/abg-interpretation) (2026).