Abstract
Programming of auditory brainstem implant (ABI) in adult patients aims for providing as many auditory electrodes as possible at most comfortable levels and preferably evoking a wide range of pitch sensation, through a standardized structured protocol. This includes repeat follow-up at defined intervals for checking of technical integrity, stable impedances, and re-arranging pitch sequence according to individual auditory development. First, nonauditory or partially auditory electrodes are checked repeatedly for acoustic input and may be selected for secondary activation.
Training is guided by specialized speech therapists, trained by the University Clinic, and comprises regular exercises with family, with mobile and computer-based programs, and repeated outpatient/inpatient training series.
Troubleshooting in case of absent sound perception or secondary failure has to consider technical defects as well as lost or displaced electrode contacts as well as degenerative processes and will lead to identification of those candidates with good prospects through revision surgery.
Outcome of patients’ acoustic abilities considers detection, discrimination, and identification of sound qualities and is evaluated regularly by standardized investigations such as loudness scaling, vowel confusion test, syllable and pattern identification by Monosyllabic-Trochee-Polysyllabic (MTP) test and word and sentence recognition by Freiburg, and Matrix and Hochmair-Schulz-Moser (HSM) tests.
Long-term improvement is a never-ending process with speech discrimination developing over days to 6 months and continuous functional increase over 3 years, and further ultra-sensitive abilities like perception of bird wings movements and of music melodies over one to several years.
Key words
auditory brainstem implants – ABI in adults – auditory perception – stimulation strategy – neurofibromatosis type 2 – stimulation side effects – Matrix test – Hochmair–Schulz–Moser test – evoked auditory brainstem response13 Programming, Rehabilitation, and Outcome Assessment for Adults: II
13.1 First Implant Activation
13.1.1 Clinical Preparation
Timing
An early temporary activation of the auditory brainstem implant (ABI) may be planned within the first 7 to 10 days after surgery. This temporary activation gives the opportunity to control the integrity of the ABI system and the impedances of the electrodes, and it may provide an early chance to the patient of experiencing some sound perception.
Before permanent activation, after surgical implantation of the ABI, a minimum period of 4 weeks is calculated for the local integration of the ABI electrode carrier within the foramen of Luschka. The first 4 to 6 weeks are regarded as the most sensitive period for electrode dislocation, either “spontaneously” or secondarily to a fall. The start of ABI activation should be planned for after this period. 1 , 2 Routinely, at 6 weeks after surgery, the date for ABI activation is scheduled and the patient is admitted for 3 days to the Comprehensive Hearing Center (CHC).
Neurological–Neurosurgical Evaluation
At the time of admittance for activation, a general clinical and neurological–neurosurgical examination is performed. Specific attention is given to the recent history of special events reported by the patient such as constant or repetitive headaches, local discomfort at the scar and implant site, signs of local inflammation, balance disturbance, vertigo, and falls.
The region of the scar and of the implant are inspected for complete healing, closed surface over the implanted parts, and for exclusion of fluid accumulation, hydrocephalus, redness or other signs of inflammation. In neurological testing, special attention is paid to caudal cranial nerves, vestibular and cerebellar functions, and exclusion of hydrocephalus.
Radiological Investigations
During the first 6 months, radiological diagnostics should be limited to cranial computed tomography (CT), while magnetic resonance imaging (MRI) is not recommended.
A first postsurgical cranial CT is recommended within the first few days after surgery, before demission from the clinic. This should exclude local hemorrhage, pneumocephalus, and brainstem displacement, and it should outline the course of the ABI cable and the location of the ABI electrode carrier. These early images will serve as a baseline for future comparison.
After 6 months of surgery, with the MED-EL device a cranial MRI is allowed under specific circumstances (Fig. 13.3 a, b). But within the 6-monthinterval after ABI implantation, MRI is to be avoided as it might cause a lead dislocation.
At re-admission for activation, in the usual case of an uneventful course during the healing period, no further cranial imaging is planned. In case of recent falls or suspicion of any inflammation or of development of a hydrocephalus, a cranial CT is indicated.
Audiological Preparations
Speech Processor
A precondition to ABI activation and programming is the selection of the adequate sound processor unit. This is done with the patient before the ABI surgery in order to arrange an activation session with it.
13.1.2 Setting at Intensive Treatment Unit (ITU) (Fig. 13.1)
Patient Monitoring and Setting with Professional Personnel
For adequate patient monitoring, first activation of a new ABI is ideally performed at the ITU in the presence of a neurosurgeon, an otolaryngologist, or a neuro-anesthesiologist, as stand-by in case of cardio-pulmonary disturbances. The patient receives a venous cannula in the forearm and is connected to continuous electrocardiogram (ECG) monitoring and pO2 monitoring. Besides, an audiologist and an electrical engineer will be present.
Technical Setup
The chosen sound processor is assembled and the connecting head piece attached. A magnet is placed in the head piece and checked for magnetic attraction. A stronger magnet can be inserted easily by the audiologist if required. The sound processor is connected to the programming platform containing the most recent fitting software ( Fig. 13.1 ).
Instructions to the Patient before and during ABI Activation
Communication during all ABI fitting sessions is enhanced/supported by the use of a large computer screen with text editing the investigator’s instructions and questions.
Before starting the ABI activation, the procedure is explained to the patient: At first, a test of the integrity of the ABI system (“reduced telemetry” setting) will be performed. The “reduced telemetry” protocol is predefined for ABI patients in the MAESTRO software. In this procedure, the integrity and coupling of the implant are assessed without stimulation at the electrode contacts.
Thereafter, each electrode will be tested, one by one, and the patient will be asked to report the perception of any sensation, be it
Some auditory sensation,
Some tinnitus or ringing sensation,
Any other sensory perception such as paresthesias, vertigo, dizziness a.s.o., or
Any combination of auditory and nonauditory effects.
These categories are noted in the activation protocol. The stimulus intensity will be increased to a comfortable loudness level and any discomfort is reported. Electrodes with some auditory impression shall be identified from nonauditory electrodes and marked in the ABI scheme (Fig. 13.3). At any unpleasant or uncomfortable sensation, this will be stopped instantaneously.
Stimulation Parameters
Stimulation via the implanted ABI is dependent on the technical characteristics of the used implant. While ABI systems by Cochlear Company apply bipolar stimulation modes, all the MED-EL Company systems perform in a monopolar mode. The recommended order of stimulation in the MED-EL electrode carrier is to start stimulating opposite electrodes as follows: E4, E9; E1, E12; E2, E3; E5, E6; E7, E8, E10, E11 ( Fig. 13.3 ).
The subsequent stimulation parameters will be adjusted highly individually:
Stimulation amplitude (current units, CU, or micro-ampere, µA),
Stimulation duration (100 to 300 µs),
Stimulation frequency (16 to 33 Hz),
Stimulation mode/strategy (FSP, HDCIS for ABI).
13.2 Implant Programming
13.2.1 Activation Procedure
Control of Implant and Electrodes
At first activation, the control of the implant integrity and its connectivity to brain structures is essential and mandatory. Only after the proof of the system integrity, programming may be started. Whenever, in future adaptation procedures, a change of the stimulation program is attempted, this control has to be implemented as the basic first step. Depending on technical integrity and on the results of the electrode testing and produced effects, one can proceed further.
In the worst of cases, if all the channels are open, one needs to deactivate the system and consider revision surgery or explantation (see below). Also, in further programming procedures, the baseline control will serve as a reference to identify possible changes within the implant or in its relation with the brainstem.
Control of Implant Integrity and Viability
The electrode impedance is tested by applying a low intensity stimulation of 300 CU (phase duration of 24.2 µs) for most recent MED-EL implant types (Synchrony, Concerto, Sonata, Pulsar) that may be perceived by the patient. In ABI patients, not all electrode contacts might provide an auditory sensation. Hence, care should be taken in performing a “full impedance” check. It is recommended to proceed to the next step (see below, Perception Level of Single Electrodes). If all tested electrodes provide an auditory effect, no side effects, and a comfortable loudness level is achieved by stimulating with more than 7.2 CU, a “full impedance” measurement can be considered. The full impedance measurement evaluates the adequate contact of the electrodes with the brainstem surface and the integrity of the whole implant.
Perception Level of Single Electrodes
A step-by-step procedure is started with stimulation of one electrode at slowly increasing stimulation amplitude; here the patient will be asked to report the threshold level and any auditory or auditory-like sensations, and, thereafter, the comfort level and the level of discomfort as well as the level and type of side effects. The applied stimulation parameter and elicited effects are documented in the stimulation protocol for each electrode by the audiologist or the technical assistant.
Repeat Electrode Check
After a first testing of all the electrodes, a brief repeat testing is performed to control the sensation levels and which electrodes provide any acoustic sensation.
13.2.2 First Programming Procedure
After success in the first activation of the ABI, an individual program has to be designed and saved to the patient’s sound processor. This program should largely exclude unpleasant side effects and enable some useful sound or noise perception. 2 , 3 , 4 , 5
Designing the First Individual ABI Program
Electrode Selection
The electrodes causing unpleasant side effects are deactivated and marked in the protocol. 1 However, they should be re-tested in future procedures as they may produce sound sensations in some patients later on. Electrodes that repeatedly produce sound or noise sensations will be switched on. The stimulation intensity is adapted according to the patient’s feedback at the most comfortable level.
Electrode Pitch
The next step involves a trial to put the electrodes in a sequence of tone heights. The patient is confronted with the sound produced by two electrodes and has to tell which gives a higher or lower pitch. Thereby, the investigator arranges the electrodes in a pitch sequence. This test is rather difficult and only a few patients will be able to complete it at first attempt.
First ABI Program
Once the auditory electrodes have been differentiated from the nonauditory ones, the latter are deactivated, and the auditory electrodes are switched on and are adjusted for their pitch and comfort levels. At the first programming, usually one ABI program is saved to the patient’s sound processor.
For orientation, before starting the individual electrode configuration, an analysis of the intraoperative EABR and compound action potentials and their levels may indicate from which electrodes successful auditory sensations will be elicited (Fig. 13.3 c). 6
Instructions to the Patient after First Programming
Basic Instructions
The patient is instructed with regard to
Handling the sound processor and the batteries,
Using the remote control, and
Increasing and decreasing the stimulation intensity.
Basic Tests
Simple tests are performed together with the patient in order to find out whether certain noises and sounds are perceived:
Low frequency noise: drumming on the table
High frequency noise: ringing of a door bell
Identification of noise construction: twofold drumming, threefold drumming
Identification of sound construction: twofold or threefold syllables: la-la, la-la-la
Then the next programming session is planned for the following day and the patient is encouraged to try out to listen to the sound processor for a couple of hours during the rest of the day.
13.2.3 Second Programming Procedure
The second ABI programming session is usually scheduled for the next morning when the patient is fit and not exhausted from other clinical investigation. This session serves for controlling whether the initial program is to be continued or needs to be changed and whether it is possible to leave the patient with it for a couple of weeks. Again, the exclusion of any unpleasant side effects and the identification of the comfortable stimulation intensity are two factors of great importance at this step and preconditions for the patient to be able to undergo hearing training during the coming weeks and months.
Adaptation of the First Individual ABI Program
First Patient Feedback
The patient reports on his/her first impressions with the activated ABI. Particularly, unpleasant sensations and the intensity of the perceived sensations are explored.
Electrode Selection
The previously selected electrodes are re-tested for sensation levels and comfort levels. If a minimum number of five electrodes are identified to give some auditory sensation, then no further electrode is tried currently.
Second ABI Program
Those electrodes that have been confirmed as auditory are kept switched on and are adjusted for sensation level and loudness. In the second programming session, live voice (produced by an audiologist) is used as reference for establishing a comfortable loudness level. It is not anticipated that the patient understands speech; it is rather the loudness perception of a periodically fluctuating stimuli such as speech which is tested. Then, the patient is prepared for expected and unexpected stimulation intensity. This can further be tested by applying very low and very high intensity noises.
One or Two ABI Programs
In some patients, early on, two different ABI programs are useful to be installed, one producing rather loud sensations and the other at lower intensity for noisy circumstances.
Instructions to the Patient at the End of the Second Programming Session
Basic Instructions
The patient is instructed for a second time with regard to
Switching on and off of the sound processor,
Increasing and decreasing stimulation intensity by using the remote control,
Changing the ABI program,
Handling the processor and the batteries,
Duration of wearing the ABI, and
Troubleshooting.
Early Tests
As on the first day, some simple tests are performed together with the patient to find out whether certain noises and sounds are perceived:
Low frequency noise: drumming on the table
High frequency noise: ringing of a door bell
Identification of noise construction: twofold drumming, threefold drumming
Identification of sound construction: twofold or threefold syllables: la-la, la-la-la
Identification of vocals: dark (A, O, U) or light vocals (E, I)
Planning the Next Steps
If the patient feels confident to handle the ABI processor and does not report any discomfort, then demission from the clinic may be planned or a third programming session is scheduled and demission is planned for thereafter. (In case of a third programming session, its schedule is equivalent to the second one.)
At demission, the patient receives:
A prescription for hearing training with a specialized speech therapist,
A date for the next programming session at about 4 weeks later,
An ABI identification card, and
An ABI booklet for him/her and his/her family doctor and local otolaryngologist.
ABI Identification Card
Patients with an implanted ABI need to carry a special implant identification card with them all the time, preferably together with their personal identification card. The implant identification card provides the patient’s identity parameters, implant type and serial number, and a phone number to be contacted in case of trauma or other emergencies.
The ABI booklet refers to the type of the patient’s personal ABI system and specifies MRI compatibility and safety checklists with regard to medical diagnostic and interventions.
Related posts:
4 Clinical Indications for ABI: Patient Selection and Alternatives
3 Imaging of the Cochlea, Cochlear Nerve, Brainstem, and AuditorySystem
6 The Retrosigmoid Approach in Auditory Brainstem Implantation
11 ABI Engineering and Intraoperative Monitoring: MED-EL
15 Auditory Brainstem Implantation in Tone Language Speakers
12 Programming, Rehabilitation, and Outcome Assessment for Adults:I
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