Near-infrared spectroscopy (NIRS) monitoring of cerebral oximetry (rSO2) provides a regional estimate of cerebral oxygen saturation. A sustained decrease in rSO2 of more than what percentage from baseline is considered a significant intraoperative threshold requiring intervention?

• A 5% below baseline
• B 10% below baseline
• C Absolute value below 60%
• D 20% relative decrease from baseline or absolute value below 50% ✓

Explanation

Published intervention thresholds for cerebral NIRS include: a relative decrease >20% from individual baseline OR an absolute rSO2 <50%. These values correlate with increased risk of postoperative neurological complications, particularly in cardiac surgery and carotid endarterectomy. Common causes of decreased rSO2 include hypotension, hypocapnia (cerebral vasoconstriction), severe anaemia, and inadvertent carotid compression. Interventions include increasing MAP, correcting hypocapnia, increasing FiO2, or blood transfusion.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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