Measurement of the Intracochlear Hypothermia Distribution Utilizing Tympanic Cavity Hypothermic Rinsing Technique in a Cochlea Hypothermia Model.

Werner Bader,Timo Gottfried,Herbert Riechelmann,Daniel Sieber,Lejo Johnson Chacko,Rudolf Glueckert,Gerald Degenhart,Joachim Schmutzhard,Romed Hoermann,Anneliese Schrott-Fischer,Natalie Fischer

doi:10.3389/fneur.2020.620691

Abstract

Introduction: Cochlea implants can cause severe trauma leading to intracochlear apoptosis, fibrosis, and eventually to loss of residual hearing. Mild hypothermia has been shown to reduce toxic or mechanical noxious effects, which can result in inflammation and subsequent hearing loss. This paper evaluates the usability of standard surgical otologic rinsing as cooling medium during cochlea implantation as a potential hearing preservation technique.Material and Methods: Three human temporal bones were prepared following standard mastoidectomy and posterior tympanotomy. Applying a retrocochlear approach leaving the mastoidectomy side intact, temperature probes were placed into the basal turn (n = 4), the middle turn (n = 2), the helicotrema, and the modiolus. Temperature probe positions were visualized by microcomputed tomography (μCT) imaging and manually segmented using Amira® 7.6. Through the posterior tympanotomy, the tympanic cavity was rinsed at 37°C in the control group, at room temperature (in the range between 22 and 24°C), and at iced water conditions. Temperature changes were measured in the preheated temporal bone. In each temperature model, rinsing was done for 20 min at the pre-specified temperatures measured in 0.5-s intervals. At least five repetitions were performed. Data were statistically analyzed using pairwise t-tests with Bonferroni correction.Results: Steady-state conditions achieved in all three different temperature ranges were compared in periods between 150 and 300 s. Temperature in the inner ear started dropping within the initial 150 s. Temperature probes placed at basal turn, the helicotrema, and middle turn detected statistically significant fall in temperature levels following body temperature rinses. Irrigation at iced conditions lead to the most significant temperature drops. The curves during all measurements remained stable with 37°C rinses.Conclusion: Therapeutic hypothermia is achieved with standard surgical irrigation fluid, and temperature gradients are seen along the cochlea. Rinsing of 120 s duration results in a therapeutic local hypothermia throughout the cochlea. This otoprotective procedure can be easily realized in clinical practice.

Highlights

Cochlea implants can cause severe trauma leading to intracochlear apoptosis, fibrosis, and eventually to loss of residual hearing
The external preparation consisted of standard surgical approach for cochlea implantation— mastoidectomy, antrotomy, and posterior tympanotomy
At constant 37◦C, the temporal bones were rinsed with standard surgical irrigation fluid over the posterior tympanotomy for 20 min at body temperature, room temperature, and iced rinsing

Summary

Introduction

Cochlea implants can cause severe trauma leading to intracochlear apoptosis, fibrosis, and eventually to loss of residual hearing. Mild hypothermia has been shown to reduce toxic or mechanical noxious effects, which can result in inflammation and subsequent hearing loss. This paper evaluates the usability of standard surgical otologic rinsing as cooling medium during cochlea implantation as a potential hearing preservation technique. Cochlea implantation (CI) is the gold standard procedure for patients with severe hearing loss. Electrode array insertion causes direct mechanical and pathophysiological intracochlear trauma [1, 2]. Electrode insertion trauma induces both fibrosis and interstitial cell proliferation forming irregular scar tissue, resulting in loss of function [2]. Otoprotective strategies inhibit inflammatory response and reduce formation of fibrotic tissue [3]

Methods

Results

Conclusion