Near-infrared spectroscopy (NIRS) cerebral oximetry shows a drop in regional cerebral oxygen saturation (rSO2) from baseline 68% to 52% during carotid endarterectomy after cross-clamping. The threshold value below which intervention is recommended is:

• A Any fall below 60%
• B Absolute drop below 40%
• C A fall of >5% from baseline
• D Absolute drop below 50% or relative drop ≥20% from baseline ✓

Explanation

Accepted intervention thresholds for cerebral NIRS during carotid endarterectomy are: absolute rSO2 below 50% OR a relative decrease of ≥20% from the individual patient's pre-induction baseline. In this case, 52% is above the absolute cutoff but the 23% relative decrease (from 68% to 52%) exceeds the 20% relative threshold, warranting intervention. Standard interventions include increasing mean arterial pressure (vasopressors), increasing FiO2, checking head position, and inserting an intraluminal shunt. NIRS measures venous-weighted (70% venous, 30% arterial) regional cerebral oxygenation, so it provides trend monitoring rather than absolute precision.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.