Change in Cerebral Blood Flow Velocity with Onset of EEG Silence during Inhalation Anesthesia in Humans: Evidence of Flow-Metabolism Coupling?

In eight subjects anesthetized with moderate to high doses of inhalation anesthetics (isoflurane or desflurane) during normocapnia, the onset of electrical silence in EEG was associated with a sudden reduction of blood flow velocity monitored from the middle cerebral artery. The magnitude of this reduction was 38 ± 11% (mean ± SD; range 24–44%). The change in EEG always preceded the change in flow velocity by 5–7 s. These observations suggest that some flow–metabolism coupling mechanism is preserved during inhalation anesthesia in humans.