QUANTITATIVE EEG-ANALYSIS AS A SUPPLEMENT TO THE CLINICAL COMA SCALE RLS85

Background: The aim of the study was to investigate the correlation be tween EEG indicators and clinical scores based on the RLS85 (Reaction Level Scale 85) in comatose patients. The results of a simple visual a ssessment of the EEG, using an arbitrary scale with typical EEG patter ns, were compared with those obtained by quantitative electroencephalo graphy (qEEG). Method: The RLS85 scores were examined in 34 patients w ith impaired consciousness due to brain tumours, vascular lesions or h ead injuries. The EEG was recorded shortly before or after the clinica l examination. The semiquantitative assessment was made by visual insp ection of the tracings, using an arbitrary scale where 12 EEG patterns with increasing proportion of slow activity were displayed. Parallel to the visual analysis, the EEGs were processed by means of EEG spectr um analysis and the power/amplitude in slow frequency bands was used a s an indicator. The results were based on correlation between various types of EEG variables and the RLS scores which were obtained in the s ame patients. Results: The correlation between the visual EEG indicato rs and coma scores ranged between 0.53 and 0.57 (P<0.01). As regards t he computerised EEG analysis, the correlation between the clinical sco res and various EEG spectrum values did not exceed 0.45 (P<0.01). A hi gher correlation could be obtained by combining eight EEG variables; t he multiple correlation coefficient was then 0.68. Conclusions: The am ount of EEG slow activity is significantly correlated to the RLS85 sco re. This means that the EEG also provides information on the level and not only on the changes of the coma degree. Surprisingly, the indicat ors based on quantitative EEG, as used in commercially available instr uments, did not give better results than the visual assessment. Howeve r, the results of the computerised analysis could be improved using mu ltivariate statistical methods. The study also showed a way to improve communication between the neurophysiologist and clinician by presenti ng the EEG findings in terms similar to those used in the clinical sca les. However, the clinician should be aware of the fact that the ''EEG score'' and the clinical score is not the same: the intention is to s upplement rather than to simulate the clinical observation.