During cardiac surgery on cardiopulmonary bypass, cerebral oximetry (rSO2) by near-infrared spectroscopy (NIRS) drops from 68% to 48%. Which intervention should be performed FIRST?

• A Increase FiO2 to 1.0 and increase ventilator rate
• B Check for correct NIRS sensor placement and patient position before changing bypass parameters
• C Administer mannitol 0.5 g/kg for cerebral oedema
• D Increase pump flow to raise MAP from 55 to ≥70 mmHg ✓

Explanation

A ≥20% relative drop in cerebral oximetry (rSO2) from baseline is a clinically significant signal. On CPB, the first intervention is to increase perfusion pressure — raising MAP to ≥70–80 mmHg by increasing pump flow or adding vasopressors — as low MAP is the most common correctable cause. Subsequent interventions in order: increase pump flow, check for correct head position (SVC/jugular venous drainage obstruction), increase FiO2, check for anaemia (transfuse if Hct <20% on CPB), check PaCO2 (hyperventilation reduces CBF). Sensor malposition should be excluded but not before addressing the most common cause.

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

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Written and medically reviewed by the StethoPrep medical team.