Early Elevation and Normalization of Electrode Impedance in Patients With Enlarged Vestibular Aqueduct Undergoing Cochlear Implantation

Abstract

Objective: To characterize early changes in impedance in patients undergoing cochlear implantation with and without enlarged vestibular aqueducts (EVA). Methods: Case-control retrospective study of patients undergoing cochlear implantation with and without EVA. Impedance was measured across all channels intraoperatively and within 24 hours of surgery. All patients received the same electrode array. Results: Ten patients with EVA (and matched controls were identified). The average intraoperative impedance across all electrodes was significantly higher in patients with EVA (13.1 AE 1.4 kV) than in controls (9.6 AE 2.5 kV, p < 0.001). At 24-hour activation, the average impedance across all electro-des was roughly equal in both groups (6.8 AE 2.7 kV versus 6.5 AE 2.1 kV, p ¼ 0.72) Conclusions: This study is the first identify differences in intraoperative impedance between patients with and without EVA. In addition, these data demonstrate rapid normalization within 24 hours of surgery. Such findings can give a window of insight into both the intracochlear microenvironment of patients with EVA and the important early electrode-fluidtissue interface changes that occur within hours of surgery for all patients.

Very early activation of cochlear implants: A review of the literature

“…Some insights can be gained from Li et al in their analysis of early activation in patients with isolated enlarged vestibular aqueduct. 21 Paradoxically, in this patient population, the authors found that impedance was higher intraoperatively, returning to levels commensurate with controls within 24 hours. Citing previous animal work, the authors theorize that differences in the electrolyte composition in the inner ear fluids may affect endocochlear potentials, and thus, the measurement of electrical resistance.…”

“…Despite the primary concern regarding the rationale behind delayed activation and the mounting body of literature on this subject, there still remains a relative paucity of surgical outcome data. Most studies do not provide granular information on postoperative clinical concerns, electing to use terms such as “no surgical complications.” 3–6,10,12,16,20,21 Other studies did not include any surgical outcome information, as their analysis focused on electrophysiological changes over the postoperative period. 9,13–15,17,18 A handful of studies have published clinical information that sheds some insight on this issue.…”

“…Most studies do not provide granular information on postoperative clinical concerns, electing to use terms such as "no surgical complications." [3][4][5][6]10,12,16,20,21 Other studies did not include any surgical outcome information, as their analysis focused on electrophysiological changes over the postoperative period. 9,[13][14][15]17,18 A handful of studies have published clinical information that sheds some insight on this issue.…”

“…Citing previous animal work, the authors theorize that differences in the electrolyte composition in the inner ear fluids may affect endocochlear potentials, and thus, the measurement of electrical resistance. 21 Irrespective of the anatomy, it may not be necessary to let the intracochlear milieu "settle," and it would appear that this already occurs within 24 hours.…”

“…5 Over the years, several other groups have published their experiences with early activation, ranging from 13 days to the day of surgery in the recovery room. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] An increasing number of publications from a select group of CI centers suggest increased acceptance of these protocols, although no data exist as to how common this practice is in reality.…”