Does early activation within hours after cochlear implant surgery influence electrode impedances?

OBJECTIVE: This study aims to determine if early device activation can influence cochlear implant electrode impedances by providing electrical stimulation within hours after cochlear implant surgery. DESIGN: Electrode impedances were measured intraoperatively, at device activation, and one-month after device activation in three groups: users whose devices were activated (1) on the same day (Same Day), (2) the next day (Next Day), and (3) 10-14 days (Standard), after cochlear implant surgery. STUDY SAMPLE: Electrode impedances are reported in fifty-one patients implanted with a Cochlear™ Nucleus® Cochlear Implant. RESULTS: Compared to intraoperative levels, impedances dropped within hours for the Same Day activation group (p < 0.001) and continued dropping on the next day after surgery (p < 0.001). Similarly, electrode impedances were significantly (p < 0.001) lower at device activation for the Next Day group as compared to their intraoperative measurements. For Standard activation, impedances increased significantly from intraoperative levels, prior to device activation (p < 0.001). One-month after initial activation, impedances were not statistically different between the Same Day, Next Day, and Standard activation groups. CONCLUSIONS: Early device activation does not influence long-term impedances in a clinically meaningful manner.

Increase in cochlear implant electrode impedances with the use of electrical stimulation.

OBJECTIVE: Electrode impedances play a critical role in cochlear implant programming. It has been previously shown that impedances rise during periods of non-use, such as the post-operative recovery period. Then when the device is activated and use is initiated, impedances fall and are typically stable. In this study, we report a new pattern where electrode impedances increase with device use and decrease with device rest. DESIGN: Electrode impedances were measured three to four times every day over a span of 1-3 months for two cochlear implant patients. STUDY SAMPLE: Two patients with a Nucleus cochlear implant participated in this study. RESULTS: Both subjects in this study show wide fluctuations in electrode impedances. By taking serial electrode impedance measurements throughout a day of use, we observe that electrode impedances consistently increase with device use and decrease with device rest. CONCLUSION: In this study, we report two cases of electrode impedances increasing as a function of device use. Numerous management strategies were employed to reduce this effect but none prevailed; a clear pathophysiologic mechanism remains elusive. Further study into the cause of this electrode impedance pattern is warranted to establish a management strategy for these cochlear implant users.

Multi-Frequency Electrocochleography and Electrode Scan to Identify Electrode Insertion Trauma during Cochlear Implantation.

Intraoperative electrocochleography (ECOG) is performed using a single low-frequency acoustic stimulus (e.g., 500 Hz) to monitor cochlear microphonics (CM) during cochlear implant (CI) electrode insertion. A decrease in CM amplitude is commonly associated with cochlear trauma and is used to guide electrode placement. However, advancement of the recording electrode beyond the sites of CM generation can also lead to a decrease in CM amplitude and is sometimes interpreted as cochlear trauma, resulting in unnecessary electrode manipulation and increased risk of cochlear trauma during CI electrode placement. In the present study, multi-frequency ECOG was used to monitor CM during CI electrode placement. The intraoperative CM tracings were compared with electrode scan measurements, where CM was measured for each of the intracochlear electrodes. Comparison between the peak CM amplitude measured during electrode placement and electrode scan measurements was used to differentiate between different mechanisms for decrease in CM amplitude during CI electrode insertion. Analysis of the data shows that both multi-frequency electrocochleography and electrode scan could potentially be used to differentiate between different mechanisms for decreasing CM amplitude and providing appropriate feedback to the surgeon during CI electrode placement.

Preoperative Imaging of Temporoparietal Scalp Thickness Predicts Off-the-Ear Sound Processor Retention in Cochlear Implants With Diametric Magnets.

OBJECTIVE: To determine if temporoparietal scalp thickness assessed via preoperative imaging predicts retention events in patients who have cochlear implants with diametric magnets and various sound processor types. STUDY DESIGN: Retrospective chart and radiological review. SETTING: Tertiary referral center. PATIENTS: One hundred forty-three adult patients who have cochlear implants with diametric magnets. MAIN OUTCOME MEASURES: Skin flap thickness, retention events, body mass index (BMI), and magnet strength. RESULTS: Of 42 patients with the most recent generation off-the-ear sound processor (OTE2), 13 (31.0%) had retention events. Of patients with a temporoparietal scalp thickness less than 8 mm, all patients could ultimately retain the device, though one of 26 was noted to have tenuous retention. Of patients with 8 to 10 mm skin flaps, 3 of 6 (50%) could not retain the device, and with more than 10 mm skin flaps, 7 of 10 (70%) could not retain the device. In the more than 10 mm group, two additional patients could not either retain the device at initial activation or were noted to have tenuous retention. Of 124 patients with behind-the-ear (BTE) sound processors, only 2 (1.6%) could not retain the device at initial activation, and 3 (2.4%) exhibited tenuous retention after 3 months of device use. Results from the first generation off-the-ear sound processor (OTE1) are also reported. CONCLUSIONS: Temporoparietal scalp thickness measured by preoperative imaging is associated with processor retention for patients with the OTE2 sound processor and diametric magnets. All patients with less than 8 mm scalp thickness could retain the OTE2, while 50% of patients with 8 to 10 mm scalp thickness and 70% with more than 10 mm scalp thickness could not retain the device. Patients should be counseled regarding their sound processor choice and/or considered candidates for skin flap reduction or other intervention as indicated. Retention events with BTE processors are rare.

Relationship Between Intraoperative Electrocochleography Responses and Immediate Postoperative Bone Conduction Thresholds in Cochlear Implantation.

OBJECTIVE: To determine the relationship between intraoperative electrocochleography (ECochG) measurements and residual hearing preservation after cochlear implant (CI) surgery by comparing differences between preoperative and immediate postoperative bone conduction thresholds. STUDY DESIGN: Prospective cohort study. SETTING: Tertiary academic referral center. PATIENTS: Sixteen patients with preoperative residual hearing and measurable (no-vibrotactile) bone conduction thresholds at 250 and/or 500 Hz who underwent cochlear implantation. MAIN OUTCOME MEASURE: Intraoperative ECochG and air and bone conduction thresholds. RESULTS: Nine patients showed no significant drop (<30%) in ECochG amplitude during CI surgery with an average preoperative and immediate postoperative BC threshold of 46 and 39 dB HL, respectively, at 500 Hz. Seven patients with a decrease in ECochG amplitude of 30% or greater showed an average preoperative 500 Hz BC threshold of 32 dB HL and immediate postoperative threshold of 55 dB HL. Air and bone conduction thresholds measured approximately 1 month after CI surgery show delayed-onset of hearing loss across our study patients. CONCLUSIONS: A small decrease (<30%) in difference response or cochlear microphonics amplitude correlates with no significant changes in immediate postoperative residual hearing, whereas patients who show larger changes (≥30%) in difference response or cochlear microphonics amplitude during intraoperative ECochG measurements show significant deterioration in BC thresholds. This study reveals the necessity of prompt postoperative bone conduction measurement to isolate the intraoperative cochlear trauma that may be detected during intraoperative ECochG measurements. Although delayed postoperative audiometrics represent longer-term functional hearing, it includes the sum of all postoperative changes during the recovery period, including subacute changes after implantation that may occur days or weeks later. Measuring air and bone conduction thresholds immediately postoperatively will better isolate factors influencing intraoperative, early postoperative, and delayed postoperative hearing loss. This will ultimately help refine surgical technique, device design, and highlight the use of intraoperative ECochG in monitoring cochlear trauma during CI surgery.

Effect of exceeding compliance voltage on speech perception in cochlear implants.

OBJECTIVES: In cochlear implants, the maximum current I (Amperes) that can be delivered on a cochlear implant electrode is determined by V = I * R, where V = compliance voltage (Volts) and R = electrode impedance (Ohms). Generally, electrode impedances are measured during each clinical visit and are used to set electrical stimulation parameters in cochlear implants. However, electrode impedances can rise during the course of cochlear implant use and lead to electrical stimulation voltage requirements exceeding the maximum compliance voltage of the medical device. Electric stimulation requirements that exceed the compliance voltage lead to clipping of the biphasic electrical pulse (current going into the cochlea) and are known to adversely affect cochlear implant outcomes. DESIGN: Thirteen (11 unilateral and 2 bilateral) Advanced Bionics cochlear implant patients with a HiRes 90k™ cochlear implant participated in this study. Speech perception scores were measured using the patient's baseline clinical program with the most comfortable loudness levels (M-levels) and the following four test programs: (1) stimulation clipped at 15% below clinical M-levels (15%C) (2) stimulation clipped at 30% below clinical M-levels (30%C) (3) M-levels decreased by 15% (15%M) and (4) M-levels decreased by 30% (30%C). Speech perception scores were measured using AzBio sentences presented at 60 dB SPL in quiet and in the presence of multi-talker babble (+10 dB SNR). RESULTS: Relative to the clinical baseline program, speech perception scores with the four test programs decreased in both quiet and noisy listening conditions. In quiet, speech perception scores measured with the 30%M and 30%C programs were significantly (p < 0.001) poorer than the baseline program. No significant differences in speech perception scores were measured between the baseline and the 15%C or 15%M programs. In the noisy listening condition, speech perception scores were significantly poorer than the baseline program for the 15%C (p = 0.008), 30%C (p < 0.001), and 30%M (p < 0.001) programs. No significant differences in speech perception scores were obtained between the baseline and the 15%M program in the noisy listening condition. Speech perception scores measured with the 30%C program were significantly (p < 0.001) poorer than those with the 30%M program, suggesting that clipping was more detrimental than reducing electrical stimulation levels. CONCLUSION: Small amounts (15%) of clipping can significantly decrease speech perception in the presence of background noise. Large amounts (30%) of both clipping and M-level reduction may lead to significantly poorer speech perception in quiet and in background noise. The decrease in speech perception scores can most likely be attributed to reduced volume and poorer spectro-temporal representation. Therefore, it is important to establish comfortably loud electrical stimulation levels without exceeding the compliance voltage to maximize cochlear implant outcomes.

Subcutaneous Air Around Receiver-Stimulator Causing Open-Circuit Failures: An Uncommon But Readily Treatable Condition Related to CPAP Use After Cochlear Implant Surgery.

OBJECTIVE: To raise awareness of a unique complication associated with continuous positive airway pressure (CPAP) use after cochlear implantation to improve early detection, prevent unnecessary testing, and facilitate treatment. STUDY DESIGN: Case series. SETTING: Tertiary referral center. SUBJECTS: Patients who developed subcutaneous air around the receiver-stimulator device and the associated ground electrode in the setting of CPAP usage, which resulted in open-circuit electrode failures. MAIN OUTCOME MEASURES: Clinical course and intervention. RESULTS: Two patients were identified that fit this criterion. Both patients were noted to have poor implant performance secondary to high or open impedances and concomitant emphysema surrounding the cochlear implant receiver-stimulator. Manual massage offered transient improvement, but programming changes ultimately led to improved sound quality and resolution of impedance anomalies in both cases. CONCLUSIONS: Subcutaneous air collection surrounding the cochlear implant receiver-stimulator in the setting of CPAP use is an uncommon but clinically relevant complication that can be recognized by characteristic physical examination findings and impedance changes. Early and accurate recognition of this event can prevent unnecessary testing and facilitate early effective treatment.

Cochlear Implantation in Craniometaphyseal Dysplasia.

OBJECTIVE: Describe the first case of cochlear implantation (CI) for auditory rehabilitation of a patient with craniometaphyseal dysplasia (CMD) and progressive mixed hearing loss. PATIENTS: A 65-year-old woman with known autosomal dominant CMD presented with progressive mixed hearing loss and declining benefit from conventional hearing aids. Computed tomography and magnetic resonance imaging revealed hyperostosis of the entire craniofacial skeleton. Hearing evaluation demonstrated pure-tone thresholds in the profound range bilaterally by air conduction, and bone conduction thresholds that matched aided thresholds for her left ear, though testing was somewhat limited by inability to mask at high air-conduction thresholds. CI candidacy testing confirmed poor word and sentence scores in the right ear. INTERVENTION: Due to the inability to access the cochlea via a conventional mastoidectomy and facial recess approach, cochlear implantation via a postauricular subtotal petrosectomy approach with ear canal overclosure was performed. MAIN OUTCOME MEASURES: Post-implantation word and sentence testing. RESULTS: Despite extensive internal auditory canal stenosis, the patient demonstrated excellent early speech understanding results 5 weeks after device activation. Postimplantation audiologic evaluation showed thresholds between 20 and 30 dB HL from 250 to 6000 Hz. Word and sentence testing scores were 76% Consonant-nucleus-consonant in quiet (up from 2% preoperatively) and 77% AzBio sentences in quiet (up from 10% preoperatively). CONCLUSION: This report describes the first description of CI for CMD. Despite the extensive radiologic abnormalities, the patient has demonstrated excellent benefit from implantation. Further study of rare temporal bone dysplasias, such as CMD, is critical to better characterize the progression of otologic disease and determine optimal treatment.