Electrical Stimulation for Cochlear Implant Selection and Rehabilitation

I. Introduction

Speech-language pathology and audiology are dynamic and expanding professions with constantly developing technological and clinical advances. Before conducting procedures involving such advances, practitioners must have acquired the knowledge, skills, education, and experience necessary to perform them competently. This policy statement is one of seven documents ^[1] developed by the Ad Hoc Committee on Advances in Clinical Practice. Each statement expresses the position of the American Speech-Language-Hearing Association (ASHA) concerning specific clinical procedures within the scope of practice of speech-language pathology or audiology, most of which have developed only within the last few years. Each statement further provides guidelines for practitioners performing these procedures. The guidelines consider the knowledge and skills normally associated with the required competencies, the clinical settings recommended for the procedure, and the appropriate involvement of personnel from other disciplines.

Clinical certification by ASHA ensures that practitioners have met the education, knowledge, and experience requirements established by the Association for providing basic clinical services in the professions of speech-language pathology or audiology. Certification in the appropriate profession is necessary, but not sufficient to perform the specific clinical procedure(s) discussed in this statement. The procedure(s) addressed in this document requires the practitioner to obtain education and training beyond that necessary for ASHA certification. Practitioners are bound by the ASHA Code of Ethics to maintain high standards of professional competence. Therefore, practitioners should engage only in those aspects of the professions that are within the scope of their competence, considering their level of education, training, and experience.

In promulgating this policy statement, there is no intention to imply that the practitioner holding ASHA Certification is prepared to conduct the procedure(s); nor is it incumbent on any certified professional to provide the procedure(s) merely because the practitioner holds certification.

The following document is intended as guidelines for the practitioner to ensure the quality of care, welfare, safety, and comfort of those served by our professions.

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II. Background

“Electrical stimulation” is the application of electrical current to the audiovestibular nerve to assess its integrity, monitor functional status of electrodes during surgery, or determine parameters for cochlear implant operation. Electrical stimulation can be an effective tool for evaluating potential candidates and designing rehabilitative parameters for implant users. These procedures include application of electrical current during promontory/round window stimulation, and cochlear implant adjustment.

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III. Purpose

The purpose of this statement is to: (a) inform audiologists that application of electrical stimulation techniques is within the scope of practice of audiologists; (b) define the series of procedures known as electrical stimulation of the audiovestibular nerve; (c) advise audiologists of the education, training, circumstances and precautions that should be considered prior to undertaking the procedures; (d) provide guidance for audiologists as to the knowledge and skills which are required to apply electrical stimulation; and (e) ultimately, to educate health care professionals, consumers and members of the general public about the services offered by audiologists as qualified health care providers.

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IV. Scope of Practice

It is the position of the American Speech-Language-Hearing Association (ASHA) that use of electrical stimulation for assessing neuroaudiologically the integrity of the audiovestibular nerve, monitoring the functional status of the implanted electrodes during surgery, and determining the parameters for cochlear implant operation are accepted clinical activities within the scope of practice of the audiologist.

The practice of audiology is evolving as it incorporates new technologic advances enabling practitioners to use more powerful tools in the diagnosis and rehabilitation of hearing-impaired persons. By identifying the use of electrical stimulation as within the scope of practice, it is not intended to limit any other new or emerging areas from being developed by audiologists or others to help improve the treatment or diagnosis of hearing loss.

If practitioners choose to perform these procedures, indicators should be developed, as part of a continuous quality improvement process, to monitor and evaluate the appropriateness, efficacy, and safety of the procedure conducted.

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V. Education and Training

Education and training may vary for each one of these procedures. The training should take place in a clinical setting allowing the professional to work with more experienced professionals and a number of patients. Each practitioner must determine whether he/she has obtained a sufficient degree and kind of education and training to be competent to perform electrical stimulation, and to deliver or facilitate the delivery of electrical current to the auditory system.

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VI. Precautions

Each practitioner should consider the following precautions or circumstances prior to undertaking these procedures:

1. Inform institutional and/or regulatory bodies, such as state licensure boards, about these procedures as within the scope of practice;

2. Check with appropriate state licensure boards to ensure that there is no limitation imposed on the scope of audiology practice that restricts the performance of electrical stimulation procedures;

3. Check professional liability insurance to ensure that there is no exclusion applicable to these procedures;

4. Obtain the informed consent of the patient and maintain complete and adequate documentation;

5. Verify in advance the electrical safety of the stimulating source. This may be carried out with a local biomedical engineering staff;

6. To prevent the risk of disease transmission from blood-borne pathogens, follow Universal Precautions, contained in the Centers for Disease Control Morbidity and Mortality Weekly Report (June 24, 1988; Perspectives in Disease Prevention and Health Promotion, 37 (24), 377–388) or ASHA's AIDS/HIV Update ( Asha, 1990); and

7. Know whom to contact in the event that emergency medical assistance is needed.

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VII. Definitions

Promontory/round window stimulation is the application of controlled current levels via an isolated electrical source to the promontory or round window niche of the middle ear. The current is delivered via an electrode that is inserted either through the tympanic membrane by myringotomy or puncture by the otolaryngologist. The audiologist provides instruction, administers current, and interprets the findings of attendant psychophysical procedures, which follow general methodologic descriptions (cf. Mecklenburg & Brimacombe, 1984). Using psychophysical methods, electrically evoked intraural muscle immittance measures, or electrically evoked brainstem potentials, the audiologist evaluates the integrity of the auditory portion of the eighth nerve. Promising research indicates that promontory/round window stimulation may assist in estimating the size of residual populations of nerve fibers (cf. Kileny et al., 1990). Based on the findings of promontory/round window stimulation and the extensive cochlear implant selection protocol, the audiologist formulates a recommendation for the ear most likely to benefit from implantation and electrical stimulation (pending no contraindications of an anatomical nature such as an ossified cochlea). Such recommendations are made within the context of case staffing by the cochlear implant team.

Depending on the device, it may also be necessary to verify electrode integrity during its/their insertion during cochlear implantation. The audiologist checks the integrity at various points during surgery, such as at the time of insertion and wound closure, to verify that the internal components will be capable of conveying electric impulses to the cochlea.

Electrical stimulation using a cochlear implant entails application of psychoacoustic methods and manufacturer's guidelines to determine optimal settings for the external signal processor. These measures may include assessment of thresholds, dynamic range, and, where applicable, pitch perceptions. The postoperative fitting procedures vary for different cochlear implant devices (Mecklenburg, Dowel, & Jenison, 1987; Norton, Eisenberg, Berliner, & Thielmeir, 1980) and for different age groups (Edgerton, 1985; Eisenberg, 1985; Eisenberg & Dye, 1987; Owens & Kessler, 1989).

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VIII. Knowledge and Skills

Each audiologist who intends to perform electrical stimulation procedures must ensure that he or she has acquired the knowledge and skills necessary to achieve each objective of the procedure.

1. Objective: To qualify patient for promontory/round window stimulation.

   Proficiency in:

   Recognizing performance that qualifies a patient for consideration for cochlear implantation.

   Knowledge/Skills needed:

   1. Knowledge of the demographic, audiologic, physiologic, anatomic, sociologic, psychological, and education variables required of a qualified prospective cochlear implantee.

   2. Knowledge of the above specific factors for patient under evaluation.

2. Objective: To obtaining informed consent to procedure (including patient, family and significant others).

   Proficiency in:

   Discussing all aspects of promontory/round window stimulation with the patient and significant others, as that procedure relates to selection for cochlear implantation.

   Knowledge/Skills needed:

   1. Knowledge of the anatomy of the auditory system, especially the middle ear (where the promontory is located), the cochlea, and auditory nerve.

   2. Knowledge of the effect of electrical current on residual nerve fibers.

   3. Knowledge of informed consent procedures.

3. Objective: To perform promontory/round window stimulation.

   Proficiency in:

   Performing psychoacoustic and electrophysiologic measures to assess the responsivity of the auditory nerve.

   Knowledge/Skills needed:

   1. Knowledge of the psychophysical methods (determination of thresholds, dynamic ranges, gap detection, temporal difference limen, adaptation) used to evaluate responsivity of the auditory nerve.

   2. Knowledge of electrophysiologic methods (electrically evoked intraural muscle immittance or electrically evoked brainstem potentials) used to evaluate responsivity of the auditory nerve.

   3. Knowledge of safe stimulus parameters to carry out the above examinations.

   4. Knowledge of patient preparation including placing surface electrodes, verifying and monitoring electrode contact.

   5. Knowledge of adverse reactions requiring adjustment in methods or termination of the procedure.

   6. Knowledge of emergency procedures, such as cardiopulmonary resuscitation (CPR).

   7. Knowledge of the interpretation of the findings of promontory/round window stimulation.

4. Objective: To counsel the patient regarding cochlear implantation.

   Proficiency in:

   Counseling skills with the profoundly hearing-impaired person and his/her family concerning cochlear implants.

   Knowledge/Skills needed:

   1. Knowledge of the limitations and benefits of cochlear implants.

   2. Knowledge of the function of various implant devices and their relative utility.

   3. Knowledge of risks entailed in implantation.

   4. Knowledge of emotional impact for patient and family as regards acceptance of cochlear implant candidacy and implantation.

5. Objective: To verify electrode integrity for intraoperative implants.

   Proficiency in:

   Using equipment and procedures that are used to check electrode integrity.

   Knowledge/Skills needed:

   1. Knowledge of techniques of application of electrodes in an operating room setting.

   2. Knowledge of operating room procedures and etiquette.

   3. Knowledge of responses to direct stimulation of electrodes, and ability to communicate these findings to the surgeon.

6. Objective: To set parameters of cochlear implant stimulation.

   Proficiency in:

   Using various tools and procedures that are utilized to set cochlear implants and to troubleshoot problems.

   Knowledge/Skills needed:

   1. Knowledge of methods to set cochlear implants using psychophysical techniques and manufacturer's guidelines.

   2. Knowledge of emotional impact on patient of initial experiences of electrical stimulation and “first hearing.”

   3. Knowledge of psychoacoustic methods to evaluate the adequacy of setting.

   4. Knowledge of maintenance requirements for each implant device and ability to communicate this information to the patient.

   5. Knowledge of adverse reactions to electrical stimulation and methods to adjust settings to minimize or eliminate them.

   6. Knowledge of malfunctions that may occur and ability to troubleshoot and correct problems.

Notes