The blood gas
For the anion gap (optional)
For oxygenation (optional)
Normal ranges used: pH 7.35–7.45, PaCO2 4.7–6.0 kPa (35–45 mmHg), HCO3 22–26, anion gap 8–12. Laboratories differ: read against your own report.
How the calculator reads the gas
It follows the same five steps as the step-by-step ABG guide: pH, then which component explains it, then whether compensation is where it should be, then the anion gap.
| Primary disorder | Expected compensation used |
|---|---|
| Metabolic acidosis | PaCO2 (mmHg) = 1.5 × HCO3 + 8 ± 2 (Winter’s formula) |
| Metabolic alkalosis | PaCO2 (mmHg) = 0.7 × HCO3 + 21 ± 2 |
| Respiratory acidosis | HCO3 + 1 per 10 mmHg (acute) to + 3.5 per 10 mmHg (chronic) |
| Respiratory alkalosis | HCO3 − 2 per 10 mmHg (acute) to − 5 per 10 mmHg (chronic) |
Anion gap = Na − (Cl + HCO3), corrected by adding 0.25 for every g/L of albumin below 40. When the gap is high, the delta ratio = (gap − 12) ÷ (24 − HCO3) looks for a second metabolic disorder.
What this calculator cannot do
It interprets numbers, not patients. It cannot tell an acute from a chronic respiratory disorder — only the history can — and it does not know whether your sample was arterial or venous. Use it to check your own reasoning, never instead of it, and never to delay treating a sick patient.