The purposes of AC are to remove as much of the tumor as possible and minimize brain dysfunction resulting from the brain tumor removal [3, 4]. Therefore, during brain mapping and monitoring, it is important to maintain a good quality of awakening in the awake phase. In the guidelines for AC, it is stated that “if the required tasks can be handled correctly, awake surgery can be performed in persons older than 65 years of age.” Regarding neurological symptoms, it is stated in the guidelines that “the patient must be able to recognize whether or not the patient can tolerate awake anesthesia.” .
Our patient was an elderly patient with a severe hearing impairment, and it was not clear whether AC was appropriate or not. We have another anesthetic option, general anesthesia with using motor evoked potentials (MEPs). However, the patient strongly desired for awake surgery, and we concluded that the patient’s obedience could be achieved if the hearing impairment problem was overcome. The patient’s preoperative cognitive function was normal (verbal I.Q. 110, performance I.Q. 103, full-scale I.Q. 108), and communication with the patient could be performed smoothly if she could hear the anesthesiologist’s instructions. Using intraoperative MEPs has been proved to be sufficient to detect the deterioration of motor function; however, there are several limitations in clinical use. First, MEPs may be insufficiently sensitive for evaluating voluntary movement under certain conditions. Suzuki et al. reported that there is a false-positive or false-negative case in evaluating with MEPs, and it should be considered that there is a discrepancy between voluntary movement and results of MEPs . Second, additional costs and human resources will be required for setting MEPs.
There has been no previous report on AC being performed with the use of a bone conduction voice amplifier. The bone conduction amplifier used in this case (authorized as a medical device, approval number: 21300BZY00587000) converts the input voice signal into bone-conducted ultrasound and directly transmits to the auditory nerve. A rechargeable lithium battery is built in the body, and there is no interference with other devices. The usefulness of the prototype device has already been proved for hearing impairment . This device is applied to the skull around the ear, and safety in use is also secured.
Using the hearing aid that the patient daily used would have the risk of contamination due to disinfection of the surgery area, breakage, and instability of fixation to the ear canal. Thus, we decided to select a bone condition amplifier. Besides, in hearing impairment cases, it is thought that a bone conduction amplifier can be used not only with the MAC method but also with the AAA method.
The surgery, in this case, might be challenging; however, we were able to perform the management of the patient successfully. In anesthetic management for AC, anesthesiologists often need to consider the diversity of patients’ backgrounds and individual differences. Considering the patient’s wish and prognosis, AC should not be rejected simply because the patient has a hearing impairment.
By using this device properly, it was possible to maintain the awakening state and to obtain sufficient obedience from the patient without noticeable complications. Using a bone conduction voice amplifier would enable AC to be completed in this case.