Empower '97: International Conference on Deaf Education
Paediatric Cochlear Implantation: the systems, the impact on deaf education and ethical considerations
Professor Barry McCormick
Director of Children's Hearing Assessment Centre, Professor in Paediatric Audiology, Queens Medical Centre, Nottingham University Hospital NHS Trust
- Brief History
- Implications for the future
- How do cochlear implants work?
- First Results
- Ethical Considerations
1 Brief History We introduced paediatric cochlear implantation to the UK in 1989 amidst great controversy. Nearly everyone seemed to be opposed to this technique but it was introduced because of service demands. A local eight year old child in our service lost his hearing after an accident and subsequently showed dramatic and worrying changes in his behaviour as he rapidly lost his natural ability to communicate. Hearing aids proved to be of no benefit because he had no residual hearing. In our search for an alternative support for this boy we found cochlear implantation after visiting other programmes around the world. The family of this local child had decided to sell their house to raise money to take him to America for the implant if it was not available in the UK.
We started the Nottingham programme as a charity and raised the money ourselves to implant and support the first seven children. With the benefit of the results on our first cases we were eventually able to obtain NHS funding for the programme and thereby place it on a more secure footing. Acceptance has now grown such that approximately one half of the children who could benefit from this procedure are now receiving cochlear implants.
Approximately one third of all children with congenital or early acquired profound deafness might benefit more from cochlear implants than from hearing aids and as the provision expands this will have a very marked effect on services for hearing impaired children. It is important, however, that programmes expand only within the context of concentrated centres of expertise particularly with the trend of implanting younger and younger children.
The group of children implanted to date includes a huge backlog of cases of older children who have passed the sensitive early stages for speech and language acquisition. These cases cannot be expected to achieve the same level of benefit as the very young who receive the extra auditory stimulation from cochlear implants in their formative years. This is not to say that older children do not receive very significant and very important support from their cochlear implants but the message for the future is that cochlear implantation will have a greater impact in the future than we can witness now. 170 children from all over the UK have now benefited from cochlear implants in our programme at Nottingham and we are now focusing our resources on the very young having declared our interest in this area and having particular expertise with the very young.
A cochlear implant bypasses damaged nerve structures in the cochlea and provides direct electrical stimulation of intact nerve pathways which conventional hearing aids cannot reach.
Cochlear implantation involves inserting an electrode array into the cochlea using standard ENT surgical techniques. The procedure is surgically reversible and re-implantation is possible. It is important, however, to be sure that the implant has the potential to provide greater stimulation than a conventional hearing aid because it will not be possible to use a hearing aid again in the implanted ear. There are no batteries in the implanted system and the experience from heart pacemakers and other implantable prostheses has benefited the development of the technology and ensured its medical safety.
Stimulation of the electrodes with minute electrical pulses from the externally worn speech processor results in complex electrical waveforms within the cochlea and these stimulate the surviving nerve endings in the auditory pathway. The electrical signals then pass along the auditory nerve to the higher centres of the brain where they are interpreted in exactly the same way as they are with normal acoustic stimulation.The implant enables a deaf person to have access to the normal speech spectrum in a very effective way. The Nucleus system, for example, analyses incoming acoustic signals from the environment and fits them into 20 frequency filter bands covering a wide range of frequency from 125 Hz up to 10 kHz (that is a much wider range than any conventional hearing aid). An electrode is allocated to each of the filter bands and at any instant of time the electrodes corresponding to the six bands containing the most energy from the incoming signal will be stimulated thus stimulating the nerve endings in those regions. This imposed pattern of stimulation is upgraded 250 times per second thus resulting in a constantly changing complex stimulation of the auditory nerve. Each electrode stimulates bundles of nerve fibres in its vicinity in an overlapping and very complex manner.
The Nucleus device has been used to illustrate one method of electrical stimulation and this is the most common system worldwide. There are other very competent devices which process the signals in different ways and the most common ones in use in the UK are the Clarion and Medel systems.
Each implant must be tuned to the child's unique requirement by determining the most appropriate lower and upper levels of electrical stimulation needed for each electrode. These threshold and comfort levels for each of the 22 electrodes must be determined using standard audiometric conditioning techniques. Such tuning can be fun and is rarely traumatic if a wide range of play materials is available in the test room.
Once tuned to the child's unique requirement (as unique to each child as a fingerprint) an aided audiogram can be obtained using standard sound field warble tone testing and we expect all children to respond at levels of 30-45 dB(A) across the speech frequency range. Although this test will confirm that the device is functioning within its design specifications it is more important to know that effective use is being made of this stimulation. Considerable attention has been paid to the development and adaptation of evaluation tools for this purpose.
(At this point a video was shown of the performance of some implanted children showing an ability to understand spoken language without lipreading or signing and the production of very clear and natural vocalisations).
4 First Results Analysis of the records of the first 100 children implanted in the Nottingham programme has revealed that after 3-5 years of implant experience 83% have speech which is intelligible to experienced listeners, 85% are able to understand common phrases without lipreading and 87% have attained functional spoken language. The majority of these children, many of whom are totally deaf without their implants, are performing as well as severely deaf very efficient hearing aid users and some are functioning like children with moderate hearing losses. Of those who are not functioning at such high levels linguistically additional (cognitive) involvements, including those following meningitis, and lack of committed auditory/aural education have been isolated as contributory factors.
Quite remarkably and somewhat unexpectedly, it has been found that after a year or so of implant use congenitally deaf children implanted early function as well as children deafened in the first few years of life.
In terms of audiological selection criteria the focus of attention has become the access, or lack of access, to high frequency sounds when using the most powerful and effective hearing aids available. If the aided thresholds at 2 kHz and 4 kHz exceed 60 dB(A) serious consideration should be given to the possibility of cochlear implantation knowing that the expected responses at these frequencies are in the region of 30-35 dB(A) through these systems. Furthermore this enhanced access to high frequency sounds is necessary for the acquisition of clear spoken language skill.
5 Ethical Considerations The term ethics refers to a group of moral principles or set of values. To act ethically you must conform to professionally endorsed principles and practices.
Fundamental to our work with very young children is the acceptance that parents must make decisions on behalf of their children. We heard a parent earlier in this conference make the plea. Don't treat parents as stupid.
Our role is to provide information so that parents can make informed choices on behalf of their children. Parents often come to our programme with considerable amounts of information and some have contacted people throughout the world, through the Internet and other sources, before deciding to consider the option of cochlear implantation. They have often already contacted friends or acquaintances in the Deaf Community and this is essential for them to form a balanced and well-informed view.
Featuring largely in the decision making process is the certain knowledge that if they wait until their child is old enough to make an informed choice they will have reduced the chances of the cochlear implant providing maximum benefit. If the auditory pathway is not stimulated during the first years of life, when a child passes through a crucial period of maximum sensitivity for language acquisition and for the development of speech production skill, the appropriate pathways may not be formed and the child might be denied the opportunity to gain maximum benefit from cochlear implantation at a later stage. It could be argued that it is unethical to allow a nervous system to fall into disuse because it is not stimulated at the critical time when it is most flexible, adaptable, and when nature has programmed it for the development of a particular skill.
It is important to clear up some misconceptions about cochlear implants. The systems are safe and they are effective. The child does not experience pain and they are often their normal selves and running about the ward the day after the operation (it is the parents who experience the pain because they are so aware of their responsibilities). Tuning the device is not a traumatic experience if handled skilfully by an experienced team. After a brief period of familiarisation children do enjoy the stimulation they receive and they quickly become dependent upon the device. Indeed those who have some degree of residual hearing, such that they can wear a hearing aid in the opposite ear, often chose to discard the hearing aid because they much prefer the stimulation through the cochlear implant.
Returning to the ethical considerations there are internationally agreed guidelines on acceptable practice for new procedures for example the 1969 Helsinki Declaration on Biomedical Research involving Human Subjects. These have been revised to include the rights of the child (adopted by the general assembly of The United Nations in November 1989). Cochlear implantation satisfies all of the principles and some of the general ones are summarised below for illustration purposes. The procedure must conform to generally accepted scientific principles. The work must be peer reviewed by independent experts. There must be full assessments of the risks and benefits. The interests of individual subjects must prevail over the interests of science and society (respecting individual dignity, privacy etc). Informed consent must be obtained and the role of the parent or legal guardian is acknowledged in this respect. Turning to more specific issues:
Article 23.1 states that a mentally or physically disabled child should enjoy a full and decent life in conditions which ensure dignity, promote self reliance, and facilitate the child's active participation in the community.
Article 23.3 states that we must ensure that the disabled child has effective access to, and receives education, training, health care services, rehabilitation services, preparation for employment, and recreation opportunities in a manner conducive to the child's achieving the fullest possible integration and individual development, including his or her cultural and spiritual development.
Article 24.1 states that no child should be deprived of his or her right of access to health services.
Article 28.1 states that no child should be deprived of his or her right of access to education services.
Article 29.1 states that the education of the child shall be directed to: a) The development of the child's personality, talents and mental and physical abilities to their fullest potential. b) The development of respect for human rights and fundamental freedoms and for the principles enshrined in the Charter of the United Nations. c) The development of respect for the child's parents, his or her own cultural identity, language and values, for the national values of the country in which the child is living, the country from which he or she may originate and for civilisations different from his or her own. d) The preparation of the child for responsible life in a free society in the spirit of understanding, peace, tolerance, equity of sexes, and friendship among all peoples ethnic, national and religious groups and persons of indigenous origin. e) The development of respect for the natural environment.
It will be appreciated that because cochlear implantation helps to expand the child's communication abilities this will have a knock on effect in helping to satisfy the principles outlined above.
Conclusion It would be unwise for the Deaf Community to deny the existence, importance and future impact of cochlear implants. If they do this they will lose public understanding and public support. It is vital that we should all help to attract more resources for those who cannot benefit from hearing aids or cochlear implants and for whom manual communication (eg British Sign Language) can be and should be an alternative natural language. We must all accept the different options and I have tried in this talk to give some justification for one alternative without in any way undermining the others. My respect for and understanding of the need for other options still remains.