Monitoring of cortical excitability during induced hypotension in aneurysm operations.
The electrical excitability of the cortex was monitored during craniotomy in 10 patients with ruptured aneurysms, to test their ability to tolerate hypotensive anesthesia. Excitability was assessed by measuring the direct cortical response, a response evoked and recorded from the surface of the brain. Previous animal experiments had shown that this response can be used as an index of cerebral blood flow. In the 10 patients the response progressively declined as the blood pressure was lowered and increased when the pressure was restored. Observation of the direct cortical response during aneurysm operations is a practical method for evaluating the electrophysiological responsiveness of the cortex during hypotension, and the authors suggest that decreases in the amplitude of the response are related to decreased in local cerebral blood flow.