Arterial Blood Gases (ABGs) can seem intimidating—but they’re a favorite topic on the NCLEX because they assess your ability to recognize life-threatening acid-base imbalances. If you’ve ever felt lost when interpreting pH, PaCO₂, or HCO₃⁻ levels, this guide is your step-by-step roadmap to ABG mastery.

What Are ABGs and Why Are They Important?

ABGs are lab tests that measure:

• pH – the acidity or alkalinity of the blood
• PaCO₂ – the partial pressure of carbon dioxide
• HCO₃⁻ – bicarbonate, a base that balances pH
• PaO₂ and O₂ sat – indicators of oxygenation

On the NCLEX, you’ll be expected to:

• Interpret ABG results
• Identify if the imbalance is respiratory or metabolic
• Determine if the body is compensating

Normal ABG Values to Memorize

3 Key Steps to Interpret ABGs (NCLEX-Friendly Method)

Step 1: Look at the pH

• < 7.35 = Acidosis
• 7.45 = Alkalosis

Step 2: Determine if it’s Respiratory or Metabolic

• CO₂ = Respiratory
• HCO₃⁻ = Metabolic

Match the abnormal value with the pH to determine the cause.

Step 3: Check for Compensation

• If the opposite system (e.g., kidneys for respiratory, lungs for metabolic) is trying to balance pH, it’s compensation.
  • Uncompensated = other value is normal
  • Partially compensated = both values abnormal, pH still off
  • Fully compensated = both values abnormal, pH normal

Common NCLEX Examples

Example 1

• pH: 7.30 (low)
• PaCO₂: 50 (high)
• HCO₃⁻: 24 (normal)

Interpretation: Respiratory Acidosis, Uncompensated

Example 2

• pH: 7.48 (high)
• PaCO₂: 32 (low)
• HCO₃⁻: 22 (normal)

Interpretation: Respiratory Alkalosis, Uncompensated

Example 3

• pH: 7.36 (normal, but slightly low)
• PaCO₂: 50 (high)
• HCO₃⁻: 30 (high)

Interpretation: Respiratory Acidosis, Fully Compensated

What the NCLEX May Ask You

• Identify the ABG imbalance
• Know the cause (e.g., hypoventilation = respiratory acidosis)
• Know the expected interventions
• Recognize when the body is compensating

Common Causes of ABG Imbalances

on’t overthink ABGs. Stick to a consistent interpretation method and practice with real scenarios. The NCLEX wants you to:

• Think critically
• Recognize patterns
• Know what actions to take based on the results

With repetition and confidence, ABGs will go from confusing to second nature.