Arterial Blood Gases

Introduction

Arterial blood gas analysis provides a rapid and accurate assessment of oxygenation, alveolar ventilation and acid-base status, the 3 processes which maintain pH homeostasis.

• The kidneys help to maintain a neutral pH by controlling bicarbonate reabsorption and elimination.
• The lung help maintain a neutral pH by controlling carbonic acid (which is directly proportional to the partial pressure of carbon dioxide) retained or released from the body.

Normal Values

Normal values for arterial blood gases

• pH: 7.35-7.45
• PaCO₂: 35-45 mm Hg
• PaO₂: 80-100 mm Hg
• HCO₃^- : 22-26 mEq/L (or mmol/L)
• SaO₂: 95-100%

Interpretation

Anion Gap

Metabolic acidosis may be associated with an increase in the anion gap.

• Anion Gap = Na⁺- Cl^- - HCO₃^-

If anion gap is more than 12 mEq/L, there is a primary metabolic acidosis regardless of pH or HCO₃^-. Some patients have a mixed acid-base disorder in which they have more than one primary disorder.

Causes and Treatment

External Links

• American Thoracic Society - Interpretation of ABGs
• Oxford Medical Education - Arterial Blood Gas (ABG) interpretation for medical students, OSCEs and MRCP PACES
  
• Australian Prescriber - The interpretation of arterial blood gases, 2010
• Interpreting arterial blood gas result, 2013
  
• RxPrep's 2024 NAPLEX Course Book for Pharmacist Licensure Exam Preparation, 2023