Abnormal Intra-operative Electrode Impedance Measurements and their Relationship with Abnormal Impedance Measurements after Switch On

Abstract

Introduction: At the end of cochlear implant surgery impedance measurements are used to check the integrity of the implant. On occasions impedance results for one or more electrodes are abnormal. The implication of these abnormal results is unclear. Objectives: To determine if abnormal electrode impedance intra-operatively is associated with abnormal test results at subsequent appointments. Material & methods:We reviewed the impedance records of 114 patients who underwent cochlear implantation with Clarion HiRes 90K or Freedom Contour advance implants in our department between 2001 and 2007. Results: 16 patients had a total of 80 electrodes with abnormal impedance on intra-operative testing. At follow up of these 16 patients only 8 still had electrodes with abnormal impedance, with a total of 9 abnormal electrodes. Clarion HiRes 90k implants were more likely than Freedom Contour advance implants to have electrodes with abnormal impedance on initial testing but their electrode impedance was more likely to have normalised by follow up. Conclusion: 89% of electrodes with abnormal intra-operative impedance testing will normalise eventually, but half of patients with abnormal electrodes when tested in theatre will have 1 or 2 non functioning electrodes long term.