Perioperative Guide
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Pulmonary Tools
ARISCATOxygenationABGWells PEPONVCURB-65Airway
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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

Enter at least one of PaO₂, PaCO₂, or HCO₃⁻ (pH alone is not sufficient)

Arterial oxygen tension from room-air ABG. Leave blank if not available.

Arterial CO₂ tension. Leave blank if not available.

Bicarbonate. Required to assess compensation pattern.

Arterial pH. Helps determine if hypercapnia is compensated or acute. Optional.

Related tools

Step 2: Review oxygenation status→ Preoperative OxygenationStep 4: Estimate postoperative pulmonary risk→ ARISCAT Pulmonary 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.

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