How well do cochlear implant intraoperative impedance measures predict postoperative electrode function?

OBJECTIVE: Objectives were as follows: 1) to evaluate the incidence of abnormal cochlear implant electrode impedance intraoperatively and at the initial activation, 2) to identify the percentage of abnormalities that resolve by the initial activation, and 3) to determine the incidence of normal intraoperative impedances that present as abnormal at the initial activation. STUDY DESIGN: Retrospective records review of intraoperative and postoperative cochlear implant electrode impedances. SETTING: Tertiary referral center. PATIENTS: Records were examined for 194 devices implanted in 165 pediatric and adult patients. RESULTS: Results indicate at least 1 open (OC) or short circuit (SC) in 12.4% (24/194) of devices intraoperatively, decreasing to 8.2% (16/194) postoperatively. OCs were more prevalent than SCs for intraoperative (92% versus 8%) and postoperative (94% versus 6%) intervals. Of the 3,430 total electrodes, 78 had abnormal impedance intraoperatively. Sixty-four of those (82%) resolved by the postoperative interval (62 OC, 2 SC), whereas 18% (14/78) remained abnormal postoperatively (12 OC, 2 SC). Six (0.17%) of 3,430 electrodes had normal impedance intraoperatively but were abnormal postoperatively. CONCLUSION: The incidence of SCs in the present study is likely underestimated because of poor sensitivity of monopolar coupling for detecting SCs. Intraoperative OCs have a high probability of resolving by the initial activation, particularly when contiguous electrodes are affected and suggests limited need for the use of a backup device in these cases. Surgical technique and/or complications, such as explant/reimplant or perilymphatic gushers, may result in increased incidence of bubbles in the cochlea and may play a role in abnormal intraoperative impedance results.