| [Objective]To research the method of recording electrically auditory brainstem responses(EABR) evoked by promontorium tympani or round window niche stimulation with needle electrode in/before cochlear implantation.[Methods]42 patients with different causes(including Inner Ear Malformation,abnormal white matter,large vestibular aqueduct Syndrome,etc) and ages were tested with EABR during cochlear implant surgery.The electrical stimulator was a modified Nucleus 24M cochlear implant which connected to a body worn speech processor.Three kinds of stimulating electrodes were used in this study,which included ball-end platinum-iridium wire electrode,promontory needle electrode and insulated nerve block needle for neurostimulation.The patients were divided into three groups(or three stages).The first group includes 17 patients whom were recorded electrically auditory brainstem responses(EABR) evoked,1) by round window membrane stimulation with ball-end electrode,and 2) by promontorium tympani or round window niche stimulation with needle electrode before cochlear implantat electrode insertion.The result of ball-end electrode stimulation was used to contrast.The objective was to optimize stimulating and recording parameters. The second group included 20 patients.After optimization of stimulating and recording parameters and method exploration,we got the EABR results from stimulating promontorium tympani or round window niche with needle electrode or nerve block needle.The third group included 5 patients.We got trans-tympanic electric auditory hrainstem response before the surgery and intra-operative EABR during surgery with promontory needle electrode or insulated nverve block needle.With modified Nucleus 24M cochlear implant connected to a body worn speech processor as the stimulation device,EABR was recorded by Bio-logic Navigator Pro evoked potential instrument.Modality of placement and location for electrodes:1)After opening facial recess and before cochlear implantation,stimulate promontorium tympani or round window niche with needle electrode or insulated nerve block needle,and stimulate round window membrane with ball-end wire electrode.2) Trans-tympanic electric auditory brainstem response before the surgery with promontory needle electrode or insulated nerve block electrode.A stimulating electrode was placed in three different positions:1) the floor of the RW niche round,2) anterior to the RW niche on the promontory and 3 ) superior to the RW niche on the promontory,which were divided into two parts:the first part for the first position and the second part for the last two positions.The results of two parts will be contrasted.Our objective was to explore and optimize the stable parameters for the trans-tympanic electric auditory brainstem response.It has been preliminarily used in some special cases.All the datas were analyzed by SPSS 11.5 statistic software.[Results]For the first group,all the patients received the positive EABR with the pulse width 50/75us.Clear EABR waveforms were recorded in all 17 cases with ball-end electrode stimulation.There were only 4 patients who got the clear EABR waveforms.9 of 17 patients with needle electrode stimulation participated in the further study,the pulse width were 50,75and 200us respectively.With the pulse width 50 or 75us,a clear EABR waveforms were recorded only in 2 cases.But with the pulse width 200us,the positive waveforms could be observed in all 9 cases.For all waveforms,wave V were the most stable to get,and waveⅢwas the second.For spherical electrode stimulation,the average latencies of waveformⅤwere 4.30±0.25ms,the average threshold was 189.20±25.80CL.And for needle electrode stimulation,the average latencies of waveformⅤwere 4.50±0.39ms,the average threshold was 170.23±13.50CL.EABR waveforms differentiation evoked by needle electrode stimulation were less than waveforms differentiation evoked by spherical electrode stimulation.Other parameters,such as rate,No of Sweeps,gain and so on influence waveform obsoletely.For the second group,clear EABR waveforms were recorded in all 20 cases with promontory needle electrode or insulated nverve block needle for neurostimulation intra-operation and before cochlear implants.WaveⅤwere recorded in all 20 cases,and waveⅢwere recorded in 10 of all 20 cases.The average latencies of waveformⅤand waveⅢandⅢ-Ⅴinterval before cochlear implantation were 4.70±0.58ms,2.91±0.45ms and 2.01±0.38ms respectively,and the average response threshold at 197.00±20.79CL,about 540uA.After cochlear implantation there was only one patient with internal acoustic canal who couldn't get EABR waveform,but neural response telemetry(NRT) was elicited.19 cases get waveⅤand 13 cases get waveⅢwith pulse width at 200us.The average latencies of waveformⅤand waveⅢandⅢ-Ⅴinterval after cochlear implantation were 4.65±0.67ms,2.66±0.61ms and 2.09±0.51ms respectively,and the average response threshold at 161.32±20.40CL,about 260uA.There were no statistic difference in waveⅤlatency,waveⅢlatency andⅢ-Ⅴinterval between before cochlear implantation and after cochlear implantation.There were no statistic difference in average waveⅤlatency and average response threshold in different positions.There was no statistic difference in average response threshold between needle electrode and insulated nverve block needle for neurostimulation.There were no statistic difference in waveⅤlatency between presence of residual hearing group and absence of residual hearing group,and between pulse width in 50us and pulse width in 200us.There were statistic difference in average response threshold between pulse width in 50us and pulse width in 200us.The dynamic current level scope before and after cochlear implantation was 24.6CL and 55C1 respectively.For the third group,clear EABR waveforms were recorded before surgery, intra-operation and after surgery.Waveforms differentiation of trans-tympanic electric auditory brainstem response Were better than waveforms differentiation during intra-operation for the same position.[Conclusion]1.Trans-tympanic electric auditory brainstem response is feasible and stable. Waveforms differentiation of trans-tympanic electric auditory brainstem response were better than waveforms differentiation during intra-operation for the same position.2.The elicitation ratio of EABR evoked by the needle electrode before cochlear implantation was coherent compared with elicitation ratio after cochlear implantation,though the waveforms differentiation were pgorer.3.Average waveⅤlatency and average response threshold in different positions between promontorium tympani or round window niche stimulation with needle electrode before cochlear implantation and EABR after cochear implantation were similar,though there were still some difference.4.Position of needle electrode stimulation and pulse width were the most important reason for elicit good waveform.5.Waveforms latency for different pulse width was similar,but the response threshold was different and waveforms differentiation was better for short pulse width.6. Needle electrode and insulated nerve block neelde for neurostimulation were all efficient for elicit EABR,but the waveform differentiation evoked by insulated nerve block needle for neurostimulation was better than needle electrode.
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