Impedance and Electrically Evoked Compound Action Potential (ECAP) Drop within 24 Hours after Cochlear Implantation

Abstract

Previous animal study revealed that post-implantation electrical detection levels significantly declined within days. The impact of cochlear implant (CI) insertion on human auditory pathway in terms of impedance and electrically evoked compound action potential (ECAP) variation within hours after surgery remains unclear, since at this time frequency mapping can only commence weeks after implantation due to factors associated with wound conditions. The study presented our experiences with regards to initial switch-on within 24 hours, and thus the findings about the milieus inside cochlea within the first few hours after cochlear implantation in terms of impedance/ECAP fluctuations. The charts of fifty-four subjects with profound hearing impairment were studied. A minimal invasive approach was used for cochlear implantation, characterized by a small skin incision (≈2.5 cm) and soft techniques for cochleostomy. Impedance/ECAP was measured intro-operatively and within 24 hours post-operatively. Initial mapping within 24 hours post-operatively was performed in all patients without major complications. Impedance/ECAP became significantly lower measured within 24 hours post-operatively as compared with intra-operatively (p<0.001). There were no differences between pre-operative and post-operative threshold for air-conduction hearing. A significant drop of impedance/ECAP in one day after cochlear implantation was revealed for the first time in human beings. Mechanisms could be related to the restoration of neuronal sensitivity to the electrical stimulation, and/or the interaction between the matrix enveloping the electrodes and the electrical stimulation of the initial switch-on. Less wound pain/swelling and soft techniques both contributed to the success of immediate initial mapping, which implied a stable micro-environment inside the cochlea despite electrodes insertion. Our research invites further studies to correlate initial impedance/ECAP changes with long-term hearing/speech performance.

Safety and feasibility of initial frequency mapping within 24 hours after cochlear implantation

“…It might be argued that many centers postpone fitting mainly because there are reports that the impedance measurements and stimulation thresholds changed during the first weeks after surgery, although one of our previous studies revealed that the variation of impedance/electrically evoked compound action potential (ECAP) at the very beginning of insertion of electrodes implied a stable micro-environment inside the cochlea after the surgery [3]. Practically this problem can be overcome by giving patients a series of maps.…”

“…To avoid possible tissue injuries, four custom-made hooks were used to expose the cortex of the mastoid bone instead of self-retaining instruments (e.g. mastoid retractor) [3]. A thin rectangular chip of cortex bone (about 20 Â 10 Â 3 mm in size) was first harvested intact from the mastoid with a chisel, and then a drill was used for mastoidectomy ( Figure 1E).…”

“…Commencement of electrical stimulation within 24 h after cochlear implantation, however, has long been performed in our department on a routine basis [3]. The idea of earlier initial mapping came from the need to sew-and-go for many of our international patients, since they tended to go home as soon as possible postoperatively in terms of economic consideration.…”

Electrophysiological Detection of Scalar-Changing Perimodiolar Cochlear Electrode Arrays: A Six-Month Follow-Up Study

“…After cochlear implantation, the electrophysiological values for impedances and t-NRT drop significantly within the first 403 24 h, followed by an increase of impedance values and a secondary slow drop of the levels [Chen et al, 2013]. The process of wound healing and the foreign body reaction of the human body to the implant can last between days and weeks after implantation [Kawano et al, 1998].…”

Effect of depth of general anesthesia on the threshold of electrically evoked compound action potential in cochlear implantation

“…Chen et al [12] found that electrically evoked compound action potential thresholds became significantly lower measured within 24 h post-operatively as compared with intra-operatively (P \ 0.001). They concluded that it may be related to the restoration of neuronal sensitivity to the electrical stimulation, and/or the interaction between the matrix enveloping the electrodes and the electrical stimulation of the initial switch-on.…”