ABG Interpretation Guide

You cannot interpret a blood gas without knowing the baseline. For the 2026 NCLEX, these are the absolute standard values you must commit to memory:

• pH: 7.35 – 7.45 (Below 7.35 is Acidotic; Above 7.45 is Alkalotic)
• PaCO2 (Respiratory): 35 – 45 mm Hg (Remember: CO2 is an acid. High CO2 = Acidotic)
• HCO3 (Metabolic/Bicarbonate): 22 – 26 mEq/L (Remember: HCO3 is a base. High HCO3 = Alkalotic)

Nurse-to-Nurse Tip: If the pH is exactly 7.40, it is perfectly normal. If it is between 7.35 and 7.39, it is normal but leaning acidic. If it is between 7.41 and 7.45, it is normal but leaning alkalotic. This matters when determining full compensation!

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The absolute fastest way to interpret ABGs on an exam is the ROME mnemonic.

Respiratory Opposite: If the primary issue is respiratory, the pH and PaCO2 will move in opposite directions.

• Respiratory Acidosis: pH ↓ and PaCO2 ↑
• Respiratory Alkalosis: pH ↑ and PaCO2 ↓

Metabolic Equal: If the primary issue is metabolic, the pH and HCO3 will move in the same (equal) direction.

• Metabolic Acidosis: pH ↓ and HCO3 ↓
• Metabolic Alkalosis: pH ↑ and HCO3 ↑

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Below is a quick-reference guide to help you link the ABG values to the clinical symptoms and common causes you will see on your exams.

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Let’s put the ROME method to the test.

Question: A patient is admitted to the emergency department with a severe panic attack and hyperventilation. The nurse draws an arterial blood gas (ABG). The results are: pH 7.52, PaCO2 28 mm Hg, and HCO3 24 mEq/L. How should the nurse interpret these findings?

• A. Uncompensated Respiratory Acidosis
• B. Uncompensated Respiratory Alkalosis (Correct)
• C. Partially Compensated Metabolic Alkalosis
• D. Fully Compensated Respiratory Alkalosis

Detailed Rationale: The correct answer is B.

1. First, look at the pH: 7.52 is high (Alkalosis).
2. Next, look at the PaCO2: 28 is low (Opposite of pH, meaning it is Respiratory).
3. Finally, look at the HCO3: 24 is normal (meaning the kidneys have not yet started to compensate). Because the pH and PaCO2 are moving in opposite directions, and the pH is outside the normal range while the HCO3 is normal, this is uncompensated respiratory alkalosis. Hyperventilation causes the patient to “blow off” too much CO2 (an acid), leading to an alkalotic state.