Acid–Base Balance & ABG
Interpretation Study Guide
I. Fundamentals
Acid: Substance that releases hydrogen ions (H+).
Base: Substance that accepts hydrogen ions (H+).
Normal Blood pH: 7.35–7.45 (below 6.8 or above 7.8 incompatible with life).
Buffers, lungs, and kidneys maintain acid–base balance.
Lungs act within minutes; kidneys act slower but longer-lasting.
II. Major Acid–Base Disorders
Respiratory Acidosis: CO2 retention → ↓pH, ↑PaCO2. Causes: COPD, airway obstruction, drug
overdose. S/S: Headache, hypotension, dysrhythmias, hyperkalemia.
Respiratory Alkalosis: CO2 loss → ↑pH, ↓PaCO2. Causes: Panic attack, hyperventilation. S/S:
Lightheadedness, paresthesia, tetany, ↓Ca+ and ↓K+.
Metabolic Acidosis: HCO3− loss or acid excess → ↓pH, ↓HCO3−. Causes: DKA, renal failure,
diarrhea. S/S: Kussmaul respirations, confusion, hyperkalemia.
Metabolic Alkalosis: HCO3− excess or acid loss → ↑pH, ↑HCO3−. Causes: Vomiting, antacids,
diuretics. S/S: Hypoventilation, muscle cramps, hypokalemia.
III. ABG Interpretation Steps
1. Look at pH (acidotic, alkalotic, or normal).
2. Look at PaCO2 (respiratory component).
3. Look at HCO3− (metabolic component).
4. Match component to pH direction.
5. Determine compensation: partial, full, or none.
6. Evaluate oxygenation via PaO2 and SaO2.
Interpretation Study Guide
I. Fundamentals
Acid: Substance that releases hydrogen ions (H+).
Base: Substance that accepts hydrogen ions (H+).
Normal Blood pH: 7.35–7.45 (below 6.8 or above 7.8 incompatible with life).
Buffers, lungs, and kidneys maintain acid–base balance.
Lungs act within minutes; kidneys act slower but longer-lasting.
II. Major Acid–Base Disorders
Respiratory Acidosis: CO2 retention → ↓pH, ↑PaCO2. Causes: COPD, airway obstruction, drug
overdose. S/S: Headache, hypotension, dysrhythmias, hyperkalemia.
Respiratory Alkalosis: CO2 loss → ↑pH, ↓PaCO2. Causes: Panic attack, hyperventilation. S/S:
Lightheadedness, paresthesia, tetany, ↓Ca+ and ↓K+.
Metabolic Acidosis: HCO3− loss or acid excess → ↓pH, ↓HCO3−. Causes: DKA, renal failure,
diarrhea. S/S: Kussmaul respirations, confusion, hyperkalemia.
Metabolic Alkalosis: HCO3− excess or acid loss → ↑pH, ↑HCO3−. Causes: Vomiting, antacids,
diuretics. S/S: Hypoventilation, muscle cramps, hypokalemia.
III. ABG Interpretation Steps
1. Look at pH (acidotic, alkalotic, or normal).
2. Look at PaCO2 (respiratory component).
3. Look at HCO3− (metabolic component).
4. Match component to pH direction.
5. Determine compensation: partial, full, or none.
6. Evaluate oxygenation via PaO2 and SaO2.
