ABG Cheat Sheet
A quick reference guide for interpreting arterial blood gases (ABGs) — including normal values, compensation patterns, and interpretation tips.
Looking to go beyond a cheat sheet? Use the ABG Calculator for real-time interpretation or practice with ABGenius to build pattern recognition.
Normal ABG Values
| Parameter | Normal Range | Represents |
|---|---|---|
| pH | 7.35 – 7.45 | Acid–base balance |
| PaCO₂ | 35 – 45 mmHg | Respiratory component |
| HCO₃⁻ | 22 – 29 mEq/L | Metabolic component |
| PaO₂ | 80 – 100 mmHg | Oxygenation |
| SaO₂ | 95 – 100% | Oxygen saturation |
Quick Interpretation Steps
- Assess pH: acidemia (<7.35) or alkalemia (>7.45)?
- Check PaCO₂ and HCO₃⁻ to identify the primary disturbance.
- Determine compensation using expected ranges (e.g., Winter’s formula or respiratory compensation rules).
- Evaluate oxygenation (PaO₂ vs FiO₂).
- Correlate findings with the clinical picture.
Compensation Rules (Summary)
- Metabolic Acidosis → Expected PaCO₂ = (1.5 × HCO₃⁻) + 8 ± 2
- Metabolic Alkalosis → PaCO₂ rises ~0.7 mmHg for every 1 mEq/L ↑ in HCO₃⁻
- Acute Resp. Acidosis → HCO₃⁻ ↑ 1 per 10 ↑ PaCO₂
- Chronic Resp. Acidosis → HCO₃⁻ ↑ 4 per 10 ↑ PaCO₂
- Acute Resp. Alkalosis → HCO₃⁻ ↓ 2 per 10 ↓ PaCO₂
- Chronic Resp. Alkalosis → HCO₃⁻ ↓ 5 per 10 ↓ PaCO₂
Clinical Tip
Always interpret ABGs in clinical context. Consider FiO₂, altitude, chronic CO₂ retention, and patient condition. A “normal” pH does not rule out a compensated disorder — always check PaCO₂ and HCO₃⁻ together.
Last updated: 2026