Arterial blood gas reaching

1. ABG Interpretation - Teaching
Module
Stepwise Approach with Clinical
Examples

2. Introduction to ABG
• Arterial Blood Gas (ABG) analysis is essential
for assessing acid–base balance, ventilation,
and oxygenation.
• Key parameters:
• - pH: 7.35 – 7.45
• - PaCO₂: 35 – 45 mmHg
• - HCO₃⁻: 22 – 26 mmol/L
• - PaO₂: 80 – 100 mmHg

3. Stepwise Interpretation of ABG
• 1. Check pH: Acidosis (<7.35) or Alkalosis
(>7.45)
• 2. Assess PaCO₂: Respiratory component
• 3. Assess HCO₃⁻: Metabolic component
• 4. Determine compensation: Acute vs. chronic
• 5. Assess oxygenation: PaO₂, A-a gradient

4. Example 1: Respiratory Acidosis
• ABG: pH 7.25, PaCO₂ 60 mmHg, HCO₃⁻ 26
mmol/L, PaO₂ 55 mmHg
• Interpretation:
• - pH < 7.35 → Acidosis
• - PaCO₂ ↑ → Respiratory cause
• - HCO₃⁻ normal → Acute, uncompensated
• Clinical scenario: COPD exacerbation,

5. Example 2: Metabolic Acidosis
• ABG: pH 7.20, PaCO₂ 30 mmHg, HCO₃⁻ 14
mmol/L, PaO₂ 90 mmHg
• Interpretation:
• - pH < 7.35 → Acidosis
• - HCO₃⁻ ↓ → Metabolic cause
• - PaCO₂ ↓ (compensatory hyperventilation)
• Clinical scenario: Diabetic ketoacidosis, septic

6. Example 3: Metabolic Alkalosis
• ABG: pH 7.55, PaCO₂ 48 mmHg, HCO₃⁻ 34
mmol/L, PaO₂ 92 mmHg
• Interpretation:
• - pH > 7.45 → Alkalosis
• - HCO₃⁻ ↑ → Metabolic cause
• - PaCO₂ ↑ (partial respiratory compensation)
• Clinical scenario: Prolonged vomiting, diuretic

7. Example 4: Respiratory Alkalosis
• ABG: pH 7.55, PaCO₂ 28 mmHg, HCO₃⁻ 23
mmol/L, PaO₂ 100 mmHg
• Interpretation:
• - pH > 7.45 → Alkalosis
• - PaCO₂ ↓ → Respiratory cause
• - HCO₃⁻ normal → Acute, uncompensated
• Clinical scenario: Anxiety, pain, hypoxemia-

8. Example 5: Mixed Disorder
• ABG: pH 7.10, PaCO₂ 55 mmHg, HCO₃⁻ 15
mmol/L, PaO₂ 60 mmHg
• Interpretation:
• - Severe acidosis (pH 7.10)
• - PaCO₂ ↑ (respiratory acidosis)
• - HCO₃⁻ ↓ (metabolic acidosis)
• → Mixed disorder (e.g., septic shock with

9. Summary: ABG Interpretation
• - Always interpret stepwise
• - Identify primary disorder (respiratory vs.
metabolic)
• - Assess compensation (acute vs. chronic)
• - Don’t forget oxygenation status
• - Always correlate with clinical scenario