Predictive Value Of Prognosis Of 40Hz Steady-state Auditory Evoked Potentials In Patients Of Massive Cerebral Infarction

BackgroundSince the first clinical usage of evoked potentials (EPs) in 1947 by Dawson GD, for its objective, convenient, easy to explain and noninvasive characters, EPs have been used widely in the clinical department of spine surgery, neurosurgery and neurological intensive care unit (NICU) as a beside monitoring technology. Brainstem auditory evoked potentials (BAEP) and short latency somatosensory evoked potentials (SLSEP) serve as effective and regular prognosis evaluating methods in the NICU for the neurocritical diseases patients because they have relatively defined origins and simple appearances, being easy to tell the difference between normal and abnormal subjects. 40Hz auditory steady-state evoked potentials (40HzaSSEP) has got attention from people since its application by Galanbos R in 1981, when it's mostly applied in the fundament researches, for example, origins of 40HzaSSEP, after which 40HzaSSEP was applied in few clinical fields such as acoustic testing in the ENT department, consciousness level monitoring in the anesthesia and limited exploratory researches in neurology. However, no applications in the NICU about 40HzaSSEP were found. This article was to study the 40HzaSSEP by testing patients of massive cerebral infarction admitted to NICU of Nanfang hospital from 2008 May to 2009 May, studying its predictive power and making comparisons between 40HzaSSEP with BAEP and SLSEP, aiming to explore the prognosis predicting value of 40HzaSSEP in patients of massive cerebral infarction.Subjects and methods143 patients admitted into NICU of Nanfang hospital d, Southern Medical University, Guangzhou from 2008 May to 2009 May were studed, 40 patients were diagnosed as massive cerebral infarction according to diagnostic criteria of <2000 Guangzhou national cerebrovascular disease monographic study about stroke's treatment according to different phases and types>. Inclusion criteria included: acute onset, diagnosed as massive cerebral infarction when admission and all the evaluations (including 40HzaSSEP, BAEP and lower limb SLSEP) could be finished within 24 h, all the patients would receive regular medical treatment except sedative medications; exclusion criteria included: patients died from factors of other systems but neurology system, infarction of cerebella or brain stem, definitely diseases of peripheral nerves, lower limbs and medulla spinals and seriously failure of liver, renal, respiratory and other systems when admission.The following information was collected for all the patients within 24 h after admission: basic demographic data (age, gender, and days of onset), major risk factors for infarction (history ill of hypertension, diabetes and past stroke) and findings of 40HzaSSEP, BAEP and lower limb SLSEP. According to the abnormal extent they were divided into three grades.①40HzaSSEP: Grade 1: bilateral wave appear; grade 2: only healthy lateral wave appears, or lesion-lateral wave lower than the other one by 50%; grade 3: neither of them appear.②BAEP: grade 1: normal bilateral wave appear at least one time and wave V are always present; grade 2: bilateral wave are abnormal but wave V are always present; grade 3: only unilateral wave V appears or even bilateral wave V disappear.③lower limb SLSEP: grade 1: bilateral P40 appear normally; grade 2: lesion lateral P40 appears heavily abnormal and healthy lateral P40 has a prolong latency, if it has; grade 3: bilateral P40 disappear.④cerebral performance categories scale (CPCs): CPC 1: Good cerebral performance: conscious, alert, able to work, might have mild neuralgic or psychological, deficit. CPC 2: Moderate cerebral disability: conscious, sufficient cerebral function for independent activities of daily life. Able to work in sheltered environment. CPC 3: Sever cerebral disability: conscious, dependent on others for daily support because of impaired brain function. It ranges from ambulatory state to severe dementia or paralysis. CPC 4: Coma or vegetative state: any degree of coma without the presence of all brain death criteria. Unawareness, even if appears awake (vegetative state) without interaction with environment; may have spontaneous eye opening and sleep/awake cycles. Cerebral unresponsiveness. CPC 5: Brain death: apnea, areflexia, EEG silence, etc. Early prognosis included two groups consist of survival and death (containing brain death) according to progression of diseases, being recover to be transferred to general neurological ward or aggravate to death. Late prognosis (3 months after onset) included favorable prognosis (CPC 1 to CPC 2) and poor prognosis (CPC 3 to CPC 5).Recording technologyWithin 24 h after admission 40HzaSSEP, BAEP and lower limb SLSEP were recorded using Viking Quest system evoked potential equipment (Nicolet Company, American). Platinum needle electrodes were applied to the head according to the 10/20 system:①40HzaSSEP: Monaural 95dB pip 39.1/s was applied through standard inserted phones, while the other ear with 70dB white noise. Two channel referencing electrode was in ipsilateral earlobes, recording electrode was in the central position (Cz), and ground electrode was in the midforehead point (FPz). Filters were set at 150-3000 Hz. Analysis time was 10 ms, overlapping 500-1000 times.②BAEP: Monaural 90dB clicks 11.1/s, overlapping 1024-2048 times, ibid.③lower limb SLSEP: the central scalp recording electrodes were placed over Cz referenced to the FPz, and the peripheral recording electrodes were positioned over the fossa poplitea point (PF) referenced to anterior patella point (K). Stimulate the posterior tibias nerve until the toes move to approximately 1 cm. overlapping 250 times in 3.1 Hz. Electrode impedance was maintained below 5 kΩ. All the tests above were operated at least twice in order to make sure the accuracy and repeatability.Statistical methods were applied for the evaluation of the obtained results: measurement data was presented as (mean±SD) and confidence interval (CI), two-sample t-test, x~2 test, Fisher's exact test and Spearman correlation analysis were used. P<0.05 was regarded as there is significant difference, and bilateral test was used. SPSS version 13.0 was applied for the statistical analysis.ResultsPrognosis prediction of stay in NICU: 40 of 143 patients admitted in NICU were analyzed, of whom 27(67.5%) were male and 13(62.5%) female, and the Fisher's exact test indicated no significant difference (P=0.175) between the survival and death groups. They aged range from 31 to 88 (63±11) years old (P=0.717, 95%CI=-6.064,8.731); The mean onset days were (4±5) days (P=0.483, 95%CI=-2.438, 5.064). Their major risk factors (including hypertension, diabetes and past stroke) appear to have no significant difference between survival and death groups according to the Fisher's exact test(P=0.527, 0.255 and 0.512 respectively ). Fisher exact test showed that survival and death groups appeared significant difference in 40HzaSSEP and lower limb SLSEP(P=0.026 and 0.033 respectively), 40HzaSSEP and lower limb SLSEP grade 3 both got the same PV+ and PV-(100% and 69.4%). BAEP grade 3 showed no significant difference (P=0.099), and PV+ was 80%, PV- was 69%. There were significant differences between 40HzaSSEP between 40HzaSSEP, BAEP and lower limb SLSEP(P=0.002 and 0.007 respectively). Spearman correlation analysis suggested there was significant correlation between 40HzaSSEP and patients' prognosis of in stay of NICU (P=0.030), while not for BAEP and lower limb SLSEP (P=0.067 and 0.071 respectively). For all the 143 patients of kinds of different extent and lesions, diffuse lesion, the prognosis of supratentorial lesion and subtentorial lesion appeared to have significant differences(P<0.001) in 40HzaSSEP by x~2 test, and the prognosis of supratentorial lesion has most relation with 40HzaSSEP while subtentorial lesion least.Prognosis after 3 months: 2 patients were missed in the follow-up because of the change of telephone number and 23 patients left in the study with 18 male (78%) and 5 female(22%), Fisher exact test showed there was no significant difference between the good and poor groups(P=0.297). they aged from 46 to 79 years old(mean age=63±9 yeas old ), and Fisher exact test showed there was no significant difference between the good and poor groups (P=0.393). The onset days between two groups were also insignificantly different (P=0.326). Their major risk factors appear to have no significant difference between survival and death groups according to the Fisher's exact test(P=0.819,0.172 and 0.608 respectively). Fisher exact test suggested there were no significant differences between grades of 40HzaSSEP with BAEP and SLSEP.Conclusion40HzaSSEP displayed high power in the prediction for patients of massive cerebral infarction, especially the 40HzaSSEP grade 3 had PV+ of 100% for the prognosis in the stay of NICU and 3 months after onset, which made certain sense in the NICU. Besides, compared with the BAEP and lower limb SLSEP, 40HzaSSEP suggested consistent power in predicting the prognosis, which indicated that it might be a useful tool for neurocritical care intensivists to assess the potential for recovery of patients of massive infarction. Furthermore, 40HzaSSEP cost less time and appeared more reliable, which would be a new method applid in the NICU, and that means further researches are need to explore the usage in the NICU. Finally, 40HzaSSEP varied depending on the extent of lesion.