Reference — Acid-Base
Normal ABG Values Reference
Quick-reference normal ranges for arterial blood gas parameters — pH, PaCO₂, HCO₃¹, PaO₂, and SaO₂ — with critical value thresholds and clinical interpretation notes.
Educational use only. Critical ABG values require immediate provider notification and clinical assessment. Reference ranges may vary slightly by institution. Always use laboratory-reported reference intervals. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Normal ABG Values
| Parameter | Normal Range | Units | Regulated By |
|---|---|---|---|
| pH | 7.35 – 7.45 | dimensionless | Lungs + Kidneys (buffer systems) |
| PaCO₂ | 35 – 45 mmHg | mmHg | Lungs (respiratory regulation) |
| HCO₃¹ | 22 – 26 mEq/L | mEq/L | Kidneys (metabolic regulation) |
| PaO₂ | 80 – 100 mmHg | mmHg | Lungs (oxygenation) |
| SaO₂ | 95 – 100% | percent | Hemoglobin oxygen saturation |
pH — Acid-Base Classification
| pH Value | Classification | Clinical Significance |
|---|---|---|
| < 6.80 | Severe acidosis — incompatible with life | Critical — immediate intervention |
| < 7.20 | Severe acidosis | Critical value — provider notification required; cardiac arrhythmia risk high |
| 7.20 – 7.34 | Acidosis | Abnormal — identify and treat cause |
| 7.35 – 7.45 | Normal | Normal range (may still be compensated) |
| 7.46 – 7.60 | Alkalosis | Abnormal — identify and treat cause |
| > 7.60 | Severe alkalosis | Critical value — provider notification required; tetany, arrhythmia, seizure risk |
PaO₂ — Oxygenation Classification
| PaO₂ (mmHg) | Classification | Clinical Response |
|---|---|---|
| 80 – 100 | Normal oxygenation | No supplemental O₂ required in healthy adults at rest |
| 60 – 79 | Mild hypoxemia | Supplemental O₂ typically indicated; assess symptoms |
| 40 – 59 | Moderate hypoxemia | Urgent intervention; supplemental O₂ required; notify provider |
| < 40 | Severe hypoxemia | Critical value — immediate provider notification; may require ventilatory support |
Note: Expected PaO₂ decreases with age. A rule of thumb: expected PaO₂ = 109 − (age × 0.43) mmHg on room air. Elderly patients may have a lower PaO₂ without pathology.
Critical ABG Values — Immediate Notification Required
pH Critical Low
< 7.20
pH Critical High
> 7.60
PaCO₂ Critical High
> 60 mmHg
PaO₂ Critical Low
< 50 mmHg
HCO₃¹ Critical Low
< 15 mEq/L
SaO₂ Critical
< 90%
Critical values require immediate provider notification, documentation of notification time, and reassessment of the patient. Follow institutional policy for critical laboratory value reporting.
Clinical Notes
- Venous vs arterial: Venous blood gas (VBG) values differ — venous pH is approximately 0.03–0.05 lower than arterial, PvCO₂ is approximately 5 mmHg higher. VBGs are used for trend monitoring but ABGs remain the standard for precise assessment.
- FiO₂ documentation: Always document the patient's FiO₂ or supplemental oxygen at time of ABG draw — the PaO₂/FiO₂ ratio (P/F ratio) is used to assess oxygenation severity. P/F < 300 = mild ARDS; < 200 = moderate; < 100 = severe.
- Temperature correction: Hyperthermia increases metabolic demand and O₂ consumption, affecting interpretation. Document patient temperature when drawing ABGs on febrile or hypothermic patients.
- COPD baseline: Patients with chronic COPD may have a chronically elevated PaCO₂ and compensatory elevated HCO₃¹ as their baseline. Assess ABGs in the context of prior results whenever available.
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with American Association for Respiratory Care (AARC) · Standard clinical chemistry / ABG references. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →