Objective To explore the feasibility of quantitative EEG parameters for prognostic prediction of patients with severe aneurysmal subarachnoid hemorrhage(SaSAH)90 d after the onset of the disease.Methods Patients with SaSAH admitted to the Neurosurgical Intensive Care Unit(NSICU)of Henan Provincial People's Hospital from September 2022 to September 2023 were prospectively consecutively enrolled,and baseline data were collected,including age,gender,medical history(hypertension,diabetes mellitus,coronary artery disease,and stroke),history of smoking,history of drinking,location of aneurysm(anterior circulation,posterior circulation),surgical modality(craniotomy,interventional surgery,hybrid surgery),Hunt-Hess classification,Glasgow coma scale(GCS)score,acute physiology and chronic health status scoring system Ⅱ(APACHE Ⅱ)score,subarachnoid hemorrhage early brain edema score(SEBES),first randomized blood glucose level after admission to NSICU,lactate level,and duration of NSICU stay.Quantitative EEG monitoring was performed in all patients within 48 h after admission to the NSICU,and amplitude-integrated electroencephalogram(aEEG)upper and lower boundaries,95％spectral edge frequency(SEF95),α change,(δ+θ)to(α+β)power ratio(DTABR),brain symmetry index(BSI),and spectral entropy were collected.Based on modified Rankin scale(mRS)scores 90 d after onset,patients were categorized into good prognosis(mRS score 2 points)and poor prognosis(mRS score 3-6 points)groups.Spearman rank correlation was used to analyze the correlation between quantitative EEG parameters and mRS scores in SaSAH patients.Multifactorial Logistic regression analysis was used to screen for correlates of poor prognosis,and receiver operating characteristic(ROC)curves were plotted to evaluate the efficacy of each index in predicting patients'poor prognosis.Results(1)A total of 72 patients with SaSAH were included,with 47 in the poor prognosis group and 25 in the good prognosis group,and the poor prognosis rate at 90 d after the onset was 65.3％.There was no statistically significant difference between the two groups in terms of gender,age,hypertension,diabetes mellitus,coronary artery disease,history of stroke,history of smoking,history of drinking,location of aneurysm,surgical modality,lactate level,and length of hospitalization in the NSICU(all P＞0.05);the differences between the Hunt-Hess grading,SEBES,and random blood glucose were statistically significant upon comparison(all P＜0.05).Compared with the good prognosis group,the changes of aEEG upper and lower boundary,SEF95,α change and spectral entropy were lower in the poor prognosis group,but DTABR and BSI were higher(all P＜0.05).(2)Spearman rank correlation analysis showed that the upper border of aEEG(r=-0.41,P＜0.01),lower border of aEEG(r=-0.54,P＜0.01),SEF95(r=-0.46,P＜0.01),α change(r=-0.53,P＜0.01)and spectral entropy(r=-0.39,P＜0.01)were negatively correlated with the mRS scores of SaSAH patients,and DTABR(r=0.52,P＜0.01)and BSI(r=0.33,P＜0.01)were positively correlated with poor prognosis of SaSAH patients.(3)The results of multifactorial Logistic regression analysis showed that Hunt-Hess grading(level Ⅳ vs.Ⅲ:OR,1.203,95％CI 1.005-1.441,P=0.044;level V vs.Ⅲ:OR,1.661,95％CI 1.109-2.487,P=0.014),SEBES(OR,1.647,95％CI 1.050-2.586;P=0.030),aEEG lower border(OR,0.687,95％CI 0.496-0.953l;P=0.024),SEF95(OR,0.436,95％CI0.202-0.937;P=0.034),α change(OR,0.368,95％CI0.189-0.717;P=0.003),DTABR(OR,1.324,95％CI 1.064-1.649;P=0.012),and BSI(OR,1.513,95％CI 1.026-2.231;P=0.036)were influencing factors of poor prognosis in SaSAH patients.ROC curve analysis showed that all of the above seven indicators had a certain predictive value for poor prognosis in SaSAH patients,among which the area under the curve of DTABR was the highest as 0.862(95％CI 0.761-0.932),with sensitivity 85.11％and specificity 80.00％.Conclusion Quantitative EEG parameters aEEG lower border,SEF95,α change,DTABR,and BSI may have certain predictive value for the short-term prognosis of SaSAH patients,which needs to be further confirmed in future multi-center large-sample studies.