Near-infrared spectroscopy (NIRS) cerebral oximetry provides regional cerebral oxygen saturation (rSO2). What rSO2 threshold below baseline warrants immediate corrective action to prevent cerebral ischaemia?

• A Any drop below 80%
• B Drop below 60% absolute value only
• C Drop of 5% from baseline
• D Absolute rSO2 <50% or relative decrease >20% from baseline ✓

Explanation

NIRS cerebral oximetry alarm thresholds: an absolute rSO2 <50% or a relative decrease >20% from pre-induction baseline are the standard intervention triggers. Corrective actions follow the 'SCORE' checklist: check SpO2, check haemoglobin/anaemia, check PaCO2 (hypocarbia causes cerebral vasoconstriction), check blood pressure (optimise cerebral perfusion pressure), check surgical causes (carotid clamp, head position). NIRS is particularly valuable during carotid endarterectomy, cardiac surgery with cardiopulmonary bypass, and beach-chair shoulder procedures where hypotension combined with Fowler position may cause cerebral ischaemia.

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

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Written and medically reviewed by the StethoPrep medical team.