ABG Interpretation Made Easy: A Quick Clinical Algorithm

 By Dr. Sk Sabir Rahaman, MBBS, MD (Pharmacology), DFM(Family Medicine), FCFM, CCEBDM, CCLSD

Arterial Blood Gas (ABG) analysis is an essential bedside tool in critical care, internal medicine, and emergency settings. It helps clinicians assess a patient’s acid-base status, ventilation efficiency, and oxygenation adequacy — all in one shot.

Yet, interpreting ABG can feel overwhelming. Here's a simplified, step-by-step algorithm designed for quick clinical decisions.

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🩺 Step-by-Step ABG Interpretation

🔹 Step 1: Evaluate pH

• pH < 7.35 → Acidosis

• pH > 7.45 → Alkalosis

🔹 Step 2: Check PaCO₂ (Respiratory Component)

• PaCO₂ > 45 mmHg → Respiratory Acidosis

• PaCO₂ < 35 mmHg → Respiratory Alkalosis

🔹 Step 3: Check HCO₃⁻ (Metabolic Component)

• HCO₃⁻ < 22 mEq/L → Metabolic Acidosis

• HCO₃⁻ > 26 mEq/L → Metabolic Alkalosis

🔹 Step 4: Identify the Primary Disturbance

Match the direction of the pH abnormality with the abnormal PaCO₂ or HCO₃⁻:

• If pH is low and PaCO₂ is high → Primary respiratory acidosis

• If pH is low and HCO₃⁻ is low → Primary metabolic acidosis
  (Same logic for alkalosis)

🔹 Step 5: Assess Compensation

• Partial Compensation → pH is still abnormal, but opposite system is adjusting

• Full Compensation → pH is normal, but PaCO₂ or HCO₃⁻ is abnormal

🔹 Step 6: Evaluate PaO₂ (Oxygenation)

• PaO₂ < 80 mmHg → Hypoxemia

• May indicate respiratory failure, V/Q mismatch, or diffusion impairment

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✅ Normal ABG Values at a Glance

Parameter	Normal Range
pH	7.35 – 7.45
PaCO₂	35 – 45 mmHg
HCO₃⁻	22 – 26 mEq/L
PaO₂	80 – 100 mmHg

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🧪 Quick Example

ABG Report:

• pH: 7.30

• PaCO₂: 50 mmHg

• HCO₃⁻: 24 mEq/L

🔍 Interpretation:

• pH < 7.35 → Acidosis

• PaCO₂ > 45 → Respiratory cause

• HCO₃⁻ normal → No compensation yet

✅ Diagnosis: Uncompensated Respiratory Acidosis

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🩻 Final Thoughts

ABG interpretation doesn't need to be intimidating. With practice and this 6-step framework, you’ll be able to identify life-threatening imbalances and respond confidently.

“ABG is not just a number game — it's the voice of a patient’s lungs, kidneys, and blood in harmony or distress.”

#ABG #ClinicalAlgorithm #CriticalCare #AcidBaseBalance #EmergencyMedicine

#SKSabirRahaman #FamilyPhysician #Pharmacologist #MedicalEducation #CBMEtools

📘 Prepared by Dr. Sk Sabir Rahaman

📍 Specialist Family Physician | Consultant Pharmacologist | Lifestyle & Diabetes Expert

📧 dr.sabir.rahaman@gmail.com 

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