In a patient undergoing carotid endarterectomy, intraoperative monitoring shows complete cessation of EEG activity. Based on the relationship between cerebral blood flow and neuronal function, EEG silence corresponds to a cerebral blood flow falling below approximately:

• A 5 mL/100 g/min
• B 20 mL/100 g/min ✓
• C 35 mL/100 g/min
• D 50 mL/100 g/min

Explanation

Normal gray matter flow is about 50 to 55 mL/100 g/min. When flow falls to roughly 20 mL/100 g/min, synaptic transmission and EEG activity fail although cell membranes remain viable; this is the penumbra zone. Flow below about 10 mL/100 g/min causes rapid membrane pump failure and infarction. A value of 50 mL/100 g/min is normal flow, and 35 mL/100 g/min still permits near-normal function.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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