ABG Interpretation 2025/2026 | Notes &
Mnemonics | Nursing & Medical Review Guide
Comprehensive Study Resource | Acid-Base Balance, pH, PaCO₂, HCO₃⁻, Compensation,
Respiratory vs. Metabolic Disorders, Clinical Scenarios | Expert-Verified | Exam & Clinical
Practice Ready
Introduction
This document provides the updated ABG Interpretation Study Guide for the 2025/2026
academic cycle. It simplifies the process of analyzing arterial blood gases through clear notes,
step-by-step interpretation strategies, and high-yield mnemonics. Key topics include normal lab
values, identification of respiratory vs. metabolic imbalances, and recognition of partial vs. full
compensation. Designed for nursing and medical students, this guide ensures confidence in both
exams and real-world clinical application.
Answer Format
Critical values, interpretation steps, and mnemonics are highlighted in bold and green for
quick reference. Practical examples are included to reinforce understanding and strengthen
rapid decision-making skills.
ABG Interpretation Guide | Verified 2025/2026 Content | Exam-Aligned | Master
Acid-Base Balance with Confidence
ABG Interpretation Study Guide 2025/2026
1. Normal ABG Values
● pH: 7.35–7.45
○ Reflects acid-base balance. Below 7.35 = acidosis; above 7.45 = alkalosis.
● PaCO₂ (partial pressure of carbon dioxide): 35–45 mmHg
○ Measures respiratory component (CO₂ = acid). High PaCO₂ = respiratory
acidosis; low PaCO₂ = respiratory alkalosis.
● HCO₃⁻ (bicarbonate): 22–26 mEq/L
○ Measures metabolic component (HCO₃⁻ = base). Low HCO₃⁻ = metabolic acidosis;
high HCO₃⁻ = metabolic alkalosis.
● PaO₂ (partial pressure of oxygen): 75–100 mmHg
○ Indicates oxygenation status.
● SaO₂ (oxygen saturation): 95–100%
○ Reflects oxygen bound to hemoglobin.
, 2. Step-by-Step ABG Interpretation (ROME Mnemonic)
● ROME: Respiratory Opposite, Metabolic Equal
○ Respiratory disorders: pH and PaCO₂ move in opposite directions (e.g., high
PaCO₂, low pH = respiratory acidosis).
○ Metabolic disorders: pH and HCO₃⁻ move in the same direction (e.g., low HCO₃⁻,
low pH = metabolic acidosis).
Steps:
1. Assess pH: Is it acidotic (<7.35) or alkalotic (>7.45)?
2. Determine Primary Disorder:
○ Check PaCO₂: High (>45 mmHg) = respiratory acidosis; low (<35 mmHg) =
respiratory alkalosis.
○ Check HCO₃⁻: Low (<22 mEq/L) = metabolic acidosis; high (>26 mEq/L) =
metabolic alkalosis.
3. Assess Compensation:
○ Respiratory compensation (for metabolic disorders): PaCO₂ adjusts to normalize
pH.
■ Metabolic acidosis: PaCO₂ decreases (hyperventilation).
■ Metabolic alkalosis: PaCO₂ increases (hypoventilation).
○ Metabolic compensation (for respiratory disorders): HCO₃⁻ adjusts over hours to
days.
■ Respiratory acidosis: HCO₃⁻ increases (kidneys retain bicarbonate).
■ Respiratory alkalosis: HCO₃⁻ decreases (kidneys excrete bicarbonate).
○ Full Compensation: pH is within normal range (7.35–7.45).
○ Partial Compensation: pH is abnormal, but compensatory parameter is
adjusting.
4. Check Oxygenation: Assess PaO₂ and SaO₂ for hypoxia.
3. Acid-Base Disorders
1. Respiratory Acidosis
○ Characteristics: pH <7.35, PaCO₂ >45 mmHg.
○ Causes: Hypoventilation (e.g., COPD, opioid overdose, pneumonia).
○ Signs: Confusion, lethargy, dyspnea.
○ Mnemonic: CHRONIC (Confusion, Headache, Respiratory depression, Opioids,
Neuromuscular weakness, Increased CO₂, Coma).
○ Interventions: Improve ventilation (e.g., BiPAP, reverse opioids with naloxone),
treat underlying cause.
2. Respiratory Alkalosis
○ Characteristics: pH >7.45, PaCO₂ <35 mmHg.
○ Causes: Hyperventilation (e.g., anxiety, hypoxia, pain).
○ Signs: Dizziness, paresthesia, tetany.
Mnemonics | Nursing & Medical Review Guide
Comprehensive Study Resource | Acid-Base Balance, pH, PaCO₂, HCO₃⁻, Compensation,
Respiratory vs. Metabolic Disorders, Clinical Scenarios | Expert-Verified | Exam & Clinical
Practice Ready
Introduction
This document provides the updated ABG Interpretation Study Guide for the 2025/2026
academic cycle. It simplifies the process of analyzing arterial blood gases through clear notes,
step-by-step interpretation strategies, and high-yield mnemonics. Key topics include normal lab
values, identification of respiratory vs. metabolic imbalances, and recognition of partial vs. full
compensation. Designed for nursing and medical students, this guide ensures confidence in both
exams and real-world clinical application.
Answer Format
Critical values, interpretation steps, and mnemonics are highlighted in bold and green for
quick reference. Practical examples are included to reinforce understanding and strengthen
rapid decision-making skills.
ABG Interpretation Guide | Verified 2025/2026 Content | Exam-Aligned | Master
Acid-Base Balance with Confidence
ABG Interpretation Study Guide 2025/2026
1. Normal ABG Values
● pH: 7.35–7.45
○ Reflects acid-base balance. Below 7.35 = acidosis; above 7.45 = alkalosis.
● PaCO₂ (partial pressure of carbon dioxide): 35–45 mmHg
○ Measures respiratory component (CO₂ = acid). High PaCO₂ = respiratory
acidosis; low PaCO₂ = respiratory alkalosis.
● HCO₃⁻ (bicarbonate): 22–26 mEq/L
○ Measures metabolic component (HCO₃⁻ = base). Low HCO₃⁻ = metabolic acidosis;
high HCO₃⁻ = metabolic alkalosis.
● PaO₂ (partial pressure of oxygen): 75–100 mmHg
○ Indicates oxygenation status.
● SaO₂ (oxygen saturation): 95–100%
○ Reflects oxygen bound to hemoglobin.
, 2. Step-by-Step ABG Interpretation (ROME Mnemonic)
● ROME: Respiratory Opposite, Metabolic Equal
○ Respiratory disorders: pH and PaCO₂ move in opposite directions (e.g., high
PaCO₂, low pH = respiratory acidosis).
○ Metabolic disorders: pH and HCO₃⁻ move in the same direction (e.g., low HCO₃⁻,
low pH = metabolic acidosis).
Steps:
1. Assess pH: Is it acidotic (<7.35) or alkalotic (>7.45)?
2. Determine Primary Disorder:
○ Check PaCO₂: High (>45 mmHg) = respiratory acidosis; low (<35 mmHg) =
respiratory alkalosis.
○ Check HCO₃⁻: Low (<22 mEq/L) = metabolic acidosis; high (>26 mEq/L) =
metabolic alkalosis.
3. Assess Compensation:
○ Respiratory compensation (for metabolic disorders): PaCO₂ adjusts to normalize
pH.
■ Metabolic acidosis: PaCO₂ decreases (hyperventilation).
■ Metabolic alkalosis: PaCO₂ increases (hypoventilation).
○ Metabolic compensation (for respiratory disorders): HCO₃⁻ adjusts over hours to
days.
■ Respiratory acidosis: HCO₃⁻ increases (kidneys retain bicarbonate).
■ Respiratory alkalosis: HCO₃⁻ decreases (kidneys excrete bicarbonate).
○ Full Compensation: pH is within normal range (7.35–7.45).
○ Partial Compensation: pH is abnormal, but compensatory parameter is
adjusting.
4. Check Oxygenation: Assess PaO₂ and SaO₂ for hypoxia.
3. Acid-Base Disorders
1. Respiratory Acidosis
○ Characteristics: pH <7.35, PaCO₂ >45 mmHg.
○ Causes: Hypoventilation (e.g., COPD, opioid overdose, pneumonia).
○ Signs: Confusion, lethargy, dyspnea.
○ Mnemonic: CHRONIC (Confusion, Headache, Respiratory depression, Opioids,
Neuromuscular weakness, Increased CO₂, Coma).
○ Interventions: Improve ventilation (e.g., BiPAP, reverse opioids with naloxone),
treat underlying cause.
2. Respiratory Alkalosis
○ Characteristics: pH >7.45, PaCO₂ <35 mmHg.
○ Causes: Hyperventilation (e.g., anxiety, hypoxia, pain).
○ Signs: Dizziness, paresthesia, tetany.
