Vasospasm is an important cause of secondary injury after subarachnoid hemorrhage (SAH), the incidence of which ranges from 40% to 70% after SAH.1 Detecting and treating vasospasm has significant potential to prevent ischemic complications from SAH. Cerebral angiography and Transcranial Doppler (TCD) ultrasound are the gold standard tests for monitoring and detecting vasospasm, but these methods cannot be used for monitoring cerebral activity and perfusion continuously. In addition, the neurological examination for high-grade patients may not be sensitive enough to detect active and threatening spasm. Thus, there is a need for a continuous modality with sufficient sensitivity.
Continuous electroencephalogram (CEEG) monitoring has been proposed to meet the need for monitoring cerebral activity and perfusion continuously (Table 1). Several studies have postulated that decrease in Radial artery (RA) variability documented on CEEG monitoring to correlate with decline in degree of cerebral blood flow (CBF) and subsequent improvement with resolution of vasospasm.3,4 Thus, changes in patterns of RA variability can predict relative changes in CBF in a continuous pattern. This observation is also supported by some animal studies that suggest a subclinical and reversible change in neuronal function to resonate with quantitative EEG changes.5,6 Vespa et al2 prospectively studied 32 acute aneurysmal SAH patients using continuous quantitative intensive care unit EEG monitoring. The authors observed that in 19 of 32 patients with documented vasospasm on cerebral angiogram, decrease in relative alpha (RA) variability was seen in all of them (P < .0016). An improvement in RA variability was seen in all 19 patients with resolution of the vasospasm after treatment initiation. In addition, 10 of 19 patients demonstrated decreased RA variability which preceded TCD/angiographic documentation by at least 2 days (mean 2.9 days, standard deviation 1.73 days), and the remaining 4 patients had same day changes of RA variability as that of TCD/angiography. The authors concluded that continuous EEG monitoring in patients with SAH can provide timely information regarding neurological dysfunction attributable to vasospasm, which is otherwise normally detected by conventional investigations.
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