| September 22, 2015 | Author: The Super Pharmacist
A cochlear implant is a medical device that helps improve the hearing of profoundly or totally deaf people by stimulating the auditory (hearing) nerve. An implant is not fully restorative and patients will not experience normal hearing, but it can give the sensation of sounds. Results vary from person to person, with some becoming more aware of environmental sounds or being able to hear speech. Cochlear implants have been evidenced to generally work particularly well for patients for adults or children who have lost their hearing after having acquired spoken language, or young children who were born deaf (1). Many patients who have implants also report being able to better control the volume and pitch of their own voice, and reporter higher levels of self-confidence (2). A cochlear implant has both an internal and external component. Externally, a microphone and speech processor is placed behind the ear with a transmitter coil worn on the side of the head. Internally, a receiver/stimulator package is surgically implanted into the mastoid bone just behind the ear that receives and translates data into electrical signals that are transmitted to electrodes situated in the cochlea. These electrodes then stimulate the spiral ganglion cells that stimulate the auditory nerve and produce the sensation of hearing.
The success rates for the implementation of the device itself is very high, with a very small possibility that the surgery will fail and at least some form of hearing improvement will not take place. Less than 0.2% of all recipients of a cochlear implant will reject the device (or choose not to use it), and approximately 0.5% of all surgeries fail and require a reimplementation of the implant (3).
As with all surgical interventions, cochlear implants do carry the risk of potential complications. A 2004 study, undertaken by a group of surgeons performing cochlear implants in the United Kingdom, reported that 25% of their patient caseload reported ‘minor’ side effects that generally resolved themselves. 6% of the cohort experienced major side effects including implant sepsis, electrode migration, implant extrusion, flap-related problems and persistent non-auditory stimulation (4). A number of other side effects have been recorded in different studies including temporary dizziness and vertigo (5), an increased risk of pneumococcal meningitis (6), and facial nerve damage (7). It is not clear what proportion of patients who have cochlear implants are affected by the more serious side effects of surgery outside of the study populations. There are a number of different rules that patients must and must not do after cochlear implementation. Given the increased risk of pneumococcal meningitis, it is imperative that all patients are offered a pneumococcal immunisation (children receiving an implant should also have their childhood immunisation schedule reviewed and completed if necessary). Infections are also relatively common after surgery, and require treatment immediately – if this is the case, patients should be administered high dose amoxicillin or amoxicillin/clavulanic acid. In more severe cases, antibiotics may be required intravenously (8). There are a number of different medical interventions that patients should avoid following implant, particularly those that involve the use of electric current or strong magnetic fields to the head or neck (i.e. TENS machines, electroconvulsive therapy, electrical hay fever relievers, and neurostimulation). MRI scans should also generally be avoided, and precautions with other devices such as security scanners and induction cookers are also advised.
The outcomes of cochlear implants often depend on a range of factors including age, type of implant, age at onset of deafness, and duration of deafness before implementation (9). The majority of studies that report cochlear implant benefits tend to focus on specific measures such as hearing and speech production, although a number of reports also consider general quality of life issues. A review of the evidence states that almost 90% of implants survive in excess of 10 years (10), and that benefits generally tend to increase with time and are multi-factorial and depend on a number of individual characteristics (11). Although there is very little formal literature regarding the role of rehabilitation in improving hearing following cochlear implants, almost all patients will have some form of multidisciplinary team input following surgery that will often involve some form of speech and language therapy, a structured set of exercises designed to help patients understand and recognise sound signals, and ongoing work at school and/or home.
Most of the literature regarding cochlear implant outcomes focuses on their implementation in children. Many children with an implant can develop spoken language and surgery is generally associated with better speech perception, production and improvement of hearing (12). Research and guidance from Western Australia’s Department of Health suggests that children who receive cochlear implants in the first year of life are able to develop language skills at a comparable rate to children with normal hearing (13). Adults who are postlingually deaf (patients who have previously been able to hear and acquired language) and receive cochlear implants report improvement in a number of quality of life indicators including better hearing, speech development and reductions in feelings of isolation and depression (14). There is a very limited evidence base regarding cochlear implants in older patients, with the limited studies that do exist tending to be all-age in focus. Most studies that have recognised benefits in older people who receive cochlear implants tend to focus on particular types of surgical implementation, with one study in the US noting that unilateral implants generally offered better outcomes to patients of all ages than the bilateral option (15). The study does not discuss any confounding variables as to why outcomes of one particular type of surgery may outweigh the benefits of the other, or discuss any of the potential additional risks that older patients may face when undergoing surgery. However, age is generally not considered a contraindication to implantation of cochlear implants as most patients will often accrue some type of benefit from the intervention if the associated risks are managed appropriately.