| Summary: | 碩士 === 國立臺灣大學 === 臨床醫學研究所 === 106 === Background
Cochlear implantation is nowadays the most promising treatment for sever to profound hearing loss. During implantation and mapping, various parameters are used to examine the integrity of the device and its surrounding environment, of which impedance is the most commonly used. Impedance, which depends on the design of the electrode, the microenvironment of scala tympani, and surrounding tissues of the electrode is a measure of electrical resistance at the electrode. It can increase because of the fibrous tissue growth around the electrode array and the fibrosis tissue formation is thought to be the cause behind post-operative increases in impedance. The increase in impedance could adversely affect cochlear implant function and power consumption.
At present, the activation timing is routinely programmed 4 to 6 weeks after surgery. Even if there are no studies or guidelines clearly explaining why it would be recommendable to wait at least 1 month before switch-on, reasons may include concerns about wound healing, magnet displacement, and electrical instability. However, soft technique electrode approaching and minimal invasive cochlear implantation are nowadays available, making early activation within 24 hours a possible management. Early activation provides patients less waiting period from rehabilitation. Besides, both the surgeon and the patient can be earlier relieved.
Objectives
Although early activation may be beneficial, there is few evidence of impact of early activation to the microenvironment in cochlear. Cochlear recovered within hours from foreign body invasion or chemical irritation was observed in animal model. Long term change of impedance after early activation remained unclear. The purpose of the study is to investigate whether early activation influences impedance and evaluate possible factors that may influence impedance.
Study Design: Case-control study.
Methods
We designed a case-control study including 40 patients from a single center who underwent cochlear implantation surgeries using devices from MED-EL Co., Innsbruck, Austria. Between July 2015 and December 2016, we prospectively enrolled 20 subjects for early activation (within 24 hours after cochlear implantation). On the other hand, 20 age- and sex-matched control subjects from the database of cochlear implantees treated with regular activation schedule (4 weeks after cochlear implantation) between November 2013 to July 2014 were retrospectively enrolled. The serial impedances of both groups were recorded and the results of the two groups were compared.
For nested data base, multiple measured impedances were analyzed by generalized estimating equation (GEE), and multivariate analysis was performed to elucidate possible factors affecting impedance measured. The criterion for statistical significance was p< 0.05.
Results
No statistical difference in long term follow up between the two groups was found using GEE for multiple measurement and multivariate analysis. Both groups reach stable impedance level in post-operative one month. Time at measurement is the factor affect long term impedance. Hearing perception improvement in post-lingual deafness patients is significant since the 1st month, but no benefit in longer follow up.
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