Arterial Blood Gas (ABG) Interpretation
Interpret arterial blood gas (ABG) results from a room-air sample before surgery. Identify ventilation patterns, acid-base compensation, and perioperative respiratory risk from PaCO₂, HCO₃⁻, and pH.
Based on: ATS · ERS
Input
Pulmonary evaluation flow: Severity → Oxygenation → ABG → Postoperative risk
Overview
A preoperative arterial blood gas drawn on room air provides three independent dimensions of respiratory assessment: oxygenation (PaO₂ vs age-expected), ventilation (PaCO₂), and the presence of chronic compensation (PaCO₂ + HCO₃⁻). This tool integrates these dimensions to produce a perioperative interpretation focused on postoperative hypoventilation risk.
Evidence Summary
The age-corrected expected PaO₂ formula (100 − age × 0.3 mmHg) provides a practical reference for room-air oxygenation. PaCO₂ >45 mmHg indicates alveolar hypoventilation and is an independent predictor of postoperative respiratory complications. When PaCO₂ elevation is accompanied by raised HCO₃⁻ (>26 mEq/L), chronic CO₂ retention with renal compensation is suggested — a pattern associated with COPD, obesity hypoventilation syndrome, and neuromuscular disease. These patients are at substantially elevated risk of postoperative respiratory failure, particularly after upper abdominal and thoracic surgery.
Learn More
Learn the pulmonary risk pathway
Review how ARISCAT, oxygenation, ABG, pneumonia severity, and postoperative respiratory risk fit together.