Ultimate NCLEX Review: ABG
Analysis & Acid-Base Balance
Cheat Sheet + Practice Problems
ABG (Arterial Blood Gas) interpretation is one of the most tested topics on the
NCLEX, and nurses must understand it to identify life-threatening imbalances
quickly. This guide gives you step-by-step rules, diagnostic patterns, easy
memory tricks, and NCLEX-style practice questions with explanations.
1. Normal ABG Values (MUST
MEMORIZE)
Component Normal Value Significance
pH 7.35 – 7.45 Acid–base balance
PaCO₂ 35 – 45 mmHg Respiratory control
HCO₃⁻ 22 – 26 mEq/L Metabolic control
PaO₂ 80 – 100 mmHg Oxygenation
SaO₂ 95 – 100% Hemoglobin oxygen saturation
,2. Step-by-Step ABG Interpretation
(NCLEX Method)
Step 1: Check pH → Acidic or Alkalotic
• pH < 7.35 = Acidosis
• pH > 7.45 = Alkalosis
Step 2: Look at PaCO₂ (Respiratory Component)
• PaCO₂ > 45 → Respiratory Acidosis
• PaCO₂ < 35 → Respiratory Alkalosis
Step 3: Look at HCO₃⁻ (Metabolic Component)
• HCO₃⁻ < 22 → Metabolic Acidosis
• HCO₃⁻ > 26 → Metabolic Alkalosis
Step 4: Match the pH
• The value (CO₂ or HCO₃⁻) that matches the pH direction identifies the
primary disorder.
Step 5: Check for Compensation
Compensation Status Meaning
Uncompensated pH is abnormal, only one abnormal value
Partially compensated pH abnormal, both CO₂ and HCO₃ abnormal
Fully compensated pH normal, but CO₂ & HCO₃ both abnormal
,3. Understanding Each Condition
🫁 Respiratory Acidosis
Cause: ↓ ventilation → ↑ CO₂ retention
Examples:
• COPD
• Asthma attack
• Pneumonia
• Respiratory depression (opioids, anesthesia)
• Head injury (↓ respiratory drive)
Signs/Symptoms:
• Hypoventilation (slow/shallow breathing)
• Confusion, drowsiness
• Warm, flushed skin
ABG Pattern:
• pH ↓
• PaCO₂ ↑
• HCO₃ normal (acute) or ↑ (chronic compensation)
NCLEX Treatment:
• Improve ventilation
• Bronchodilators
• Reversal agents (Naloxone for opioid overdose)
,🫁 Respiratory Alkalosis
Cause: Hyperventilation → ↓ CO₂
Examples:
• Anxiety attack
• Pain
• High fever
• Early salicylate poisoning
• Mechanical ventilation too high
Signs/Symptoms:
• Rapid breathing
• Light-headedness
• Tingling fingers
ABG Pattern:
• pH ↑
• PaCO₂ ↓
NCLEX Treatment:
• Calm breathing → paper bag breathing NOT recommended anymore unless
instructed by provider
• Rebreathing mask (if ordered)
• Reduce ventilator settings
⚡ Metabolic Acidosis
Cause: Loss of base or buildup of acids
Examples:
• DKA (diabetic ketoacidosis)
• Renal failure
• Diarrhea (loss of bicarbonate)
• Shock / sepsis (lactic acidosis)
, Signs/Symptoms:
• Kussmaul respirations (deep & rapid breathing)
• Hypotension
• Confusion
ABG Pattern:
• pH ↓
• HCO₃⁻ ↓
NCLEX Treatment:
• Treat underlying cause
• Insulin for DKA
• IV fluids
• Sodium bicarbonate (only in severe cases)
✨ Metabolic Alkalosis
Cause: Loss of acid or excess bicarbonate
Examples:
• Vomiting
• NG suctioning
• Diuretics
• Excess antacids
Signs/Symptoms:
• Hypoventilation (lungs try to keep CO₂)
• Muscle cramps
• Hypokalemia signs (weakness, arrhythmias)
ABG Pattern:
• pH ↑
• HCO₃⁻ ↑
Analysis & Acid-Base Balance
Cheat Sheet + Practice Problems
ABG (Arterial Blood Gas) interpretation is one of the most tested topics on the
NCLEX, and nurses must understand it to identify life-threatening imbalances
quickly. This guide gives you step-by-step rules, diagnostic patterns, easy
memory tricks, and NCLEX-style practice questions with explanations.
1. Normal ABG Values (MUST
MEMORIZE)
Component Normal Value Significance
pH 7.35 – 7.45 Acid–base balance
PaCO₂ 35 – 45 mmHg Respiratory control
HCO₃⁻ 22 – 26 mEq/L Metabolic control
PaO₂ 80 – 100 mmHg Oxygenation
SaO₂ 95 – 100% Hemoglobin oxygen saturation
,2. Step-by-Step ABG Interpretation
(NCLEX Method)
Step 1: Check pH → Acidic or Alkalotic
• pH < 7.35 = Acidosis
• pH > 7.45 = Alkalosis
Step 2: Look at PaCO₂ (Respiratory Component)
• PaCO₂ > 45 → Respiratory Acidosis
• PaCO₂ < 35 → Respiratory Alkalosis
Step 3: Look at HCO₃⁻ (Metabolic Component)
• HCO₃⁻ < 22 → Metabolic Acidosis
• HCO₃⁻ > 26 → Metabolic Alkalosis
Step 4: Match the pH
• The value (CO₂ or HCO₃⁻) that matches the pH direction identifies the
primary disorder.
Step 5: Check for Compensation
Compensation Status Meaning
Uncompensated pH is abnormal, only one abnormal value
Partially compensated pH abnormal, both CO₂ and HCO₃ abnormal
Fully compensated pH normal, but CO₂ & HCO₃ both abnormal
,3. Understanding Each Condition
🫁 Respiratory Acidosis
Cause: ↓ ventilation → ↑ CO₂ retention
Examples:
• COPD
• Asthma attack
• Pneumonia
• Respiratory depression (opioids, anesthesia)
• Head injury (↓ respiratory drive)
Signs/Symptoms:
• Hypoventilation (slow/shallow breathing)
• Confusion, drowsiness
• Warm, flushed skin
ABG Pattern:
• pH ↓
• PaCO₂ ↑
• HCO₃ normal (acute) or ↑ (chronic compensation)
NCLEX Treatment:
• Improve ventilation
• Bronchodilators
• Reversal agents (Naloxone for opioid overdose)
,🫁 Respiratory Alkalosis
Cause: Hyperventilation → ↓ CO₂
Examples:
• Anxiety attack
• Pain
• High fever
• Early salicylate poisoning
• Mechanical ventilation too high
Signs/Symptoms:
• Rapid breathing
• Light-headedness
• Tingling fingers
ABG Pattern:
• pH ↑
• PaCO₂ ↓
NCLEX Treatment:
• Calm breathing → paper bag breathing NOT recommended anymore unless
instructed by provider
• Rebreathing mask (if ordered)
• Reduce ventilator settings
⚡ Metabolic Acidosis
Cause: Loss of base or buildup of acids
Examples:
• DKA (diabetic ketoacidosis)
• Renal failure
• Diarrhea (loss of bicarbonate)
• Shock / sepsis (lactic acidosis)
, Signs/Symptoms:
• Kussmaul respirations (deep & rapid breathing)
• Hypotension
• Confusion
ABG Pattern:
• pH ↓
• HCO₃⁻ ↓
NCLEX Treatment:
• Treat underlying cause
• Insulin for DKA
• IV fluids
• Sodium bicarbonate (only in severe cases)
✨ Metabolic Alkalosis
Cause: Loss of acid or excess bicarbonate
Examples:
• Vomiting
• NG suctioning
• Diuretics
• Excess antacids
Signs/Symptoms:
• Hypoventilation (lungs try to keep CO₂)
• Muscle cramps
• Hypokalemia signs (weakness, arrhythmias)
ABG Pattern:
• pH ↑
• HCO₃⁻ ↑
