Development of quantitative evaluation factors for determining the level of facial muscle relaxation in rabbits using facial muscle electromyography

Permanent facial nerve damage is one of the most critical complications that can occur during otologic and neurosurgical procedures. As a result, facial nerve monitoring equipment is now used in most of otologic surgeries. The monitoring devices used for this purpose usually evaluate the activity of facial muscle in response to stimulation to the facial nerve. For these purposes, electromyography and the train-of-four (TOF) method is commonly used clinically, but these approaches have an important limitation: this qualitative method only depends on visual information of finger movement. Thus, in this study, a new factor that can be used to quantitatively the stage of muscle relaxation at the facial nerve was developed based on the degree of muscle relaxation and electro-stimulation. Ketamine intravenous anesthesia and isoflurane inhalation anesthesia was given to 13 rabbits. A 28 G unipolar needle-electrode was inserted at an exposed facial nerve, and stimulated (0.1 mA - 5.0 mA) with an electrical stimulator. Also, the degree of muscle relaxation based electromyographic signal acquisition was performed while increasing the dose of neuromuscular blockades. After data noise reduction and normalization, the collected EMG signals were divided into 33 variables, and a new evaluation factor was developed using statistical methods based on multiple linear regression models and principal component analysis. A new evaluation factor was identified that can be used to quantitatively estimate each phase in muscle relation. The evaluating factors that were calculated in accordance with the electrical simulation resulted in improved results (r = 0.96) when compared to the existing assessment methods. (T1 ratio r = 0.72; T4/T1 ration r = 0.52).