Oxygenation Assessment
Evaluate preoperative oxygenation status from SpO₂ and PaO₂ against age-adjusted expected values. Determine whether oxygenation impairment warrants further workup or arterial blood gas (ABG) testing.
Based on: ATS · ERS
Input
Pulmonary evaluation flow: Severity → Oxygenation → ABG → Postoperative risk
Overview
Preoperative oxygenation assessment extends beyond a single SpO₂ reading. By combining age-corrected expected PaO₂, arterial blood gas values, and P/F ratio, clinicians can quantify the degree of respiratory reserve reduction in each patient. This tool integrates available measurements to support a structured clinical interpretation.
Evidence Summary
The age-expected PaO₂ formula (100 − age × 0.3 mmHg) provides a practical reference for room-air arterial oxygen tension. The formula reflects the physiological decline in PaO₂ with ageing due to increasing V/Q mismatch, reduced alveolar surface area, and decreased elastic recoil. SpO₂ is non-invasively available but does not measure ventilatory adequacy or PaCO₂. The P/F ratio (PaO₂/FiO₂) is a standardised oxygenation index used in ARDS definitions and perioperative risk stratification; values below 300 indicate impaired oxygenation efficiency.