Arterial Blood Gas Interpretation
Enter arterial pH, PaCO₂, bicarbonate, and serum electrolytes to evaluate acid-base disorders, compensation, and anion gap.
Normal range 7.35–7.45
Normal range 35–45 mmHg
Normal range 22–26 mEq/L
Include serum sodium
Include serum chloride
Optional; defaults to 4 g/dL
Optional; improves delta-gap analysis
Primary disorder
Primary respiratory acidosis
Compensation assessment
Acute expected HCO₃⁻ ≈ 25.5; chronic expected HCO₃⁻ ≈ 30.0. Compare to actual to judge chronicity.
Corrected anion gap
14.0 mEq/L
Delta gap analysis
Delta gap within expected range for isolated high-anion-gap metabolic acidosis.
Clinical recommendations
- Confirm laboratory values and assess for sample handling errors.
- Assess airway, ventilation, and CNS status. Consider naloxone if opioid-induced.
- Provide ventilatory support as indicated and monitor for hypercapnia complications.
- Delta gap within expected range for isolated high-anion-gap metabolic acidosis.
How to Use This Calculator
Collect arterial blood gas and serum chemistries
Use the same blood draw whenever possible to minimise time-dependent changes in acid-base status.
Enter lab values accurately
Include albumin to correct the anion gap. Lactate improves delta-gap calculations but is optional.
Use results with clinical context
Combine the calculator output with patient history, physical exam, ventilation status, and serial ABG measurements.
Formula
Anion gap = Na⁺ − Cl⁻ − HCO₃⁻
Corrected anion gap = (Measured AG) + 2.5 × (4 − albumin)
Winter’s formula (metabolic acidosis compensation) = 1.5 × HCO₃⁻ + 8 ± 2
Respiratory compensation formulas and delta-gap analysis are summarised in the output.
Full Description
Acid-base interpretation starts with identifying the primary disturbance via pH, followed by assessing compensation and evaluating the anion gap for metabolic acidosis. Correcting the anion gap for albumin avoids underestimating high-anion-gap acidosis in hypoalbuminemia. Delta-gap analysis reveals mixed disorders, guiding further diagnostic workup and treatment decisions. Always correlate calculator results with clinical findings and serial laboratory trends.
Frequently Asked Questions
Why correct the anion gap for albumin?
Albumin is a major unmeasured anion. Each 1 g/dL decrease lowers the gap by ~2.5 mEq/L, masking high-anion-gap acidosis in hypoalbuminemic patients.
How accurate is Winter’s formula?
It predicts PaCO₂ compensation for metabolic acidosis within ±2 mmHg. Deviations suggest a secondary respiratory disorder.
Can I apply this to venous blood gases?
Arterial values are preferred. Venous gases may be approximated but require caution, especially for PaCO₂ interpretation.
What if albumin isn’t available?
Assume albumin 4 g/dL for a quick estimate, but note that hypoalbuminemia may mask high-anion-gap acidosis.