Clinical application of compressed spectral array in long-term EEG monitoring of comatose patients

To obtain continuous information about the cerebral electrical activity in the early course of coma, an apparatus was designed which included a small fast computer capable of calculating the Fourier transform. The practical application of this system of CSA to 123 comatose patients in a neurosurgical intensive care unit overcame the technical difficulties connected both with the patient's and environmental conditions. The advantages of such a technique are mainly due to its capacity of synthetising EEG signals and to its clarity of presentation, which is easily grasped even by people not specifically trained in electroencephalography. Hours of EEG activity are compressed into a pictorial and synoptic representation that shows in real time the distribution and temporal behaviour of frequencies as well as the intensity of total electrical activity. The immediate detection of these parameters permits evaluation of any worsening or improvement of cerebral electrogenesis, as well as of the inter-hemispheric asymmetries at their onset. EEG monitoring thus provides useful elements for assessing the comatose state in individual cases and for adjusting treatment. Finally, the spectrographic aspect of the first 48 h, as a whole, carries a great prognostic significance. The most striking finding from this study was the confirmation that the comatose states that, in their early course, show only a fixed slow-wave EEG activity are far more rare than those that display an electrical activity changing in time.