Arterial Blood Gas (ABG) — Normal Values and Interpretation

Arterial blood gas tests measure the levels of oxygen, carbon dioxide, and the pH of the blood. Here are the normal values:

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✅ Normal ABG Values:

Parameter	Normal Range	Meaning
pH	7.35 – 7.45	Blood acidity/alkalinity
PaCO₂	35 – 45 mmHg	Partial pressure of CO₂ (respiratory)
HCO₃⁻	22 – 26 mEq/L	Bicarbonate (metabolic)
PaO₂	80 – 100 mmHg	Partial pressure of O₂
SaO₂	95 – 100%	Oxygen saturation
Base Excess	-2 to +2 mEq/L	Buffering capacity

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How to Analyze ABG Results

To interpret ABG values systematically, follow this four-step method:

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Step 1: Evaluate the pH

• A pH below 7.35 indicates acidosis.
• A pH above 7.45 indicates alkalosis.
• A pH between 7.35 and 7.45 is considered normal, but subtle abnormalities may still be present if other values are off.

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Step 2: Assess PaCO₂ (Respiratory Component)

• PaCO₂ represents the respiratory influence on pH.
• High PaCO₂ (>45 mmHg) suggests respiratory acidosis (hypoventilation).
• Low PaCO₂ (<35 mmHg) suggests respiratory alkalosis (hyperventilation).

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Step 3: Assess HCO₃⁻ (Metabolic Component)

• HCO₃⁻ reflects the metabolic (renal) regulation of acid-base balance.
• Low HCO₃⁻ (<22 mEq/L) indicates metabolic acidosis.
• High HCO₃⁻ (>26 mEq/L) suggests metabolic alkalosis.

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Step 4: Determine Compensation

• If one system (respiratory or metabolic) is out of range but the pH is still normal, it means the other system is compensating.
• Uncompensated: pH is abnormal, and only one component is off.
• Partially compensated: pH is still abnormal, but both PaCO₂ and HCO₃⁻ are altered.
• Fully compensated: pH is normal, but both PaCO₂ and HCO₃⁻ are out of range.

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Sample Interpretation

ABG Report:

• pH: 7.30
• PaCO₂: 48 mmHg
• HCO₃⁻: 24 mEq/L

Interpretation:

• The pH is low → indicates acidosis.
• PaCO₂ is high → supports respiratory acidosis.
• HCO₃⁻ is within normal range → no metabolic compensation yet.

🟩 Conclusion: This is a case of uncompensated respiratory acidosis.