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.