University of Edinburgh
 

Cochlear Implant Update

Presented on Thursday, 12 May 2011

Arlene O'Malley, Clinical Scientist

Bilateral Cochlear Implants

Traditionally patients in the UK have been offered unilateral cochlear implants.

Bilateral implants were only offered to:

  • meningitic patients (risk of ossification)
  • dual sensory impairment

NICE Recommendations
Jan 2009 NICE issued new guidance on the provision of Cochlear Implants for adults and children.

  • New paediatric patients being considered for cochlear implantation will be offered CI's for both ears. This should be carried out as a single procedure (simultaneously).
  • Existing paediatric CI users will be offered a second implant (sequentially).

Recommendation will be reviewed

Normal binaural hearing

Made possible by several sub-phenomena:

  • Head shadow effect
    • Physical phenomenon
    • Sounds arrive at ears at different times
    • Head acts as an acoustic barrier
  • Binaural redundancy effects due to summation
  • Binaural squelch effect
  • Inter-aural differences – in time and intensity level

Unilateral Cochlear Implant

Compare to single-sided deafness

  • Difficulty localising sounds.
  • Greater difficulty understanding speech in all listening environments.
  • CI's not able to provide "normal" hearing.
  • CI user cannot hear with the same sensitivity or speech understanding in all acoustic environments as a normal hearing person.

Unilateral CI

  • Sound originates on opposite ear
  • Head shadow effect 10-20dB less
  • Typical conversation 50dB
  • Hearing thresholds 20-30dB better to optimally understand
  • Cochlear Implant hearing thresholds around 30dB
  • Real world background noise

Expected Benefits of Bilateral Implantation

  • Improved localisation of sound
  • Improved speech understanding in quiet
  • Improved speech understanding in background noise
  • Stimulation of both auditory pathways
  • A guarantee that the better hearing ear has been implanted
  • Improvements in speech, language and auditory development in children
  • In the event that one device fails, the patient is not left without sound
  • Improved enjoyment of music
  • Subjective reports of a more natural sound
    Litovsky et al: Bilateral cochlear implants in adults and children. Arch
    Otolaryngol Head Neck Surg. 2004 May;130(5):648-55
    Tyler et al: Update on bilateral cochlear implantation. Curr Opin Otolaryngol
    Head Neck Surg. 2003 Oct;11(5):388-93

Limitations of Bilateral Cochlear Implants

  • Fitted with 2 separate cochlear implants
  • Lack the time dependent synchronisation of normal hearing listeners.
  • Incoming signal is filtered into numerous frequency bands.
  • Current processing strategies discard some of the low frequency (fine structure) information used by the binaural system.
  • Binaural benefits may be reduced if period of auditory deprivation prior to being implanted.

Considerations for simultaneous bilateral cochlear implantation

  • Ability to utilise future medical treatments – hair cell regeneration/stem cell treatment
  • New technology likely to occur in child's lifetime

"Given that binaural hearing depends on bilateral input during a critical development period, if the second ear does not receive auditory input during the critical period of cortical development, later technology, no matter how advanced, will only provide input to a cortex incapable of receiving it."
B Robert Peters MD Dallas Otolaryngology CI Program

Scottish Cochlear Implant Programme – Uptake of Simultaneous Bilateral Implants

  • 1st year – 30% uptake
  • 2nd year – 76% uptake
  • 3rd Year – 80% uptake

Sequential Bilateral Implants - Factors to consider

  • Duration of deafness between ears
  • Neural plasticity – Is there a critical age during which to implant the second side?

Studies show an improvement in listening in background noise and localisation of sound (head shadow effect)
Zeitler et al 2008

Will patients have the ability to access binaural hearing? (interaural timing cues)

Some studies have concluded long delays between implants - may not give full benefits of bilateral implants
Tyler et al 2007; Laske et al 2009

All existing paediatric CI users at the time of the NICE guidelines were considered for a sequential CI.

  • Sequential Cochlear Implant Profile completed for each patient.
  • Discussed with patient and family to allow them to make an informed choice.

Sequential Cochlear Implant Profile

  • Fitness for general anaesthesia
  • Otology
  • Consistent unilateral CI use established
  • Child's ability to participate in Mapping sessions
  • Commitment to long-term follow up
  • Development of functional spoken language
  • Hearing history
  • Degree of Concern: None, Mild/Moderate or Great

Based on profile a recommendation would be given:

  • Not a candidate
  • Unlikely to benefit
  • Degree of benefit uncertain
  • Has the potential to Benefit

Profile used as a counselling tool to allow family to make an informed choice.

Sequential Bilateral CI's

Group 1 – those who have acquired a hearing loss in both ears after developing spoken language. These children have had previous experience of processing spoken language with two ears.

Group 2 – those who were under the age of 5 on 29th of Jan 2009 and have had hearing problems since birth.

Group 3 – those over the age of 5 on 29th of Jan 2009 and have had hearing problems since birth, starting with the youngest first.

Sequential Bilateral CI's – patient counselling

  • Realistic expectations of what 2nd implant will sound like.
  • Establishing consistent wearing of the 2nd device.
  • Following training program to get maximum benefit for 2nd device.

Sequential Bilateral CI's - appointments

  • 2nd operation carried out.
  • 4 weeks to switch on of second device.
  • Additional programming appointments to achieve optimal MAP on 2nd ear.
  • Future double appointments to program both processors.

Sequential Implant Training Programme

Issued to all sequential implant patients

Climbing the progress ladder

progress ladder

  1. First step to establish consistent wearing of the device.
  2. Second step to wear only the new processor for a short period each day.
  3. Third step to increase the amount of time wearing only the new processor each day
  4. Focused listening – gradually increasing the time from 10-30 mins each day.
  5. Listening to reading from a book.
  6. Conversing during dinner time.

Climbing the progress ladder

Our Experience

  • Majority of children find sequential switch on difficult.
  • Counselling patient and parents
  • Realistic expectations
  • Importance of consistent use of both devices

Adolescent Sequential Bilateral Recipients

  • BCIG 2011 Nottingham CI Program present results of adolescent questionaire following sequential bilateral CI.
  • All appreciated 2nd implant enhanced their listening
  • Majority thought they could locate sounds easier.
  • Group conversation – majority thought it was easier.
  • Quality of life had increased.
  • Confidence from having a back-up processor.
  • BUT Most struggled on their journey to become full-time users of the 2nd implant.

Current Research

Scottish CI Programme is one of three centres to be enrolled in bilateral implant study. (Bradford and Cambridge CI programmes).

Using the University of York Crescent of sound.

  • Designed for use in clinics to administer tests of spatial hearing.
  • Ability to localise sound.
  • To track moving sounds.
  • Benefit from the head shadow.
  • For adults – measure ability of listeners to attend to one talker when several talkers are speaking at the same time.
  • Can be used for adults and paediatrics.

University of York Crescent of Sound

Summary

  • Bilateral Implants – two ears are better than one!
  • Sequential bilateral Implants – only on offer to unilateral CI users at the time of the NICE recommendations.
  • Simultaneous bilateral Implants – will be offered to all paediatric patients provided there are no contraindications.
  • Future developments: Further research studies to quantify benefit for different patient populations.