The ABG interpreter analyses arterial blood gas values to identify acid-base disorders, including respiratory acidosis, respiratory alkalosis, metabolic acidosis, metabolic alkalosis, and fully or partially compensated states. ABG interpretation is a core critical care nursing skill tested in NCLEX and applied daily in ICU, ED, and respiratory wards. Enter the pH, PaCO₂, HCO₃⁻, and optional PaO₂ to get an instant interpretation with clinical context.
| Parameter | Normal Range |
|---|---|
| pH | 7.35 – 7.45 |
| PaCO₂ | 35 – 45 mmHg |
| HCO₃⁻ | 22 – 26 mEq/L |
| PaO₂ | 80 – 100 mmHg |
| SpO₂ | 95 – 100% |
Step 1 — pH: <7.35 = acidosis, >7.45 = alkalosis, 7.35–7.45 = normal.
Step 2 — PaCO₂: >45 = respiratory acidosis cause, <35 = respiratory alkalosis cause.
Step 3 — HCO₃⁻: <22 = metabolic acidosis cause, >26 = metabolic alkalosis cause.
Step 4 — Match: Which value matches the pH direction? That is the primary disorder. If both are abnormal in the same pH direction, partial compensation has occurred.
Step 1 — Check pH (acidosis <7.35, alkalosis >7.45). Step 2 — Check PaCO₂ (>45 = respiratory acidosis cause, <35 = respiratory alkalosis cause). Step 3 — Check HCO₃⁻ (<22 = metabolic acidosis cause, >26 = metabolic alkalosis cause). Step 4 — Match the abnormal value to the pH direction to find the primary disorder. If both are abnormal, compensation has begun.
Normal ABG values: pH 7.35–7.45, PaCO₂ 35–45 mmHg, HCO₃⁻ 22–26 mEq/L, PaO₂ 80–100 mmHg, SpO₂ ≥95%.