The Healthy Hearing Program Diagnostic Assessment Protocols for Audiological Practice

Transcription

1 The Healthy Hearing Program Diagnostic Assessment Protocols for Audiological Practice Edited by Tegan Keogh Co-Edited by Nuala Beahan 1

2 FOREWORD The following diagnostic protocols represent information supported by relevant and most recent scientific literature. The broader aim is to establish a gold standard of practice amongst paediatric diagnostic audiologists which facilitates evidence based clinical practice. Document Revision History: Version Date Prepared By Comments 1 1/12/2009 Tegan Keogh Review in June 2010, and 6 monthly thereafter. and Nuala Beahan Approvals: 1 Version Name Title/Responsibility Date Signature Anticipated Reviews: Who When Audiology Working Group June

3 ACKNOWLEDGEMENTS The editor of this document wishes to acknowledge that the following sections are heavily drawn, with permission, from the United Kingdom s NHSP s Neonatal Hearing Assessment Protocols. Sections one to eight (i-viii) are replications of the NHSP protocol, with some amendment for application, to the Queensland State-wide Healthy Hearing Program. The following 1. Stevens, J (ed). (2008). Auditory Brainstem Response Testing in Babies using Clicks: A recommended test protocol (version 2.0), 2. Mason, S (ed). (2002). Auditory Brainstem Response Testing in Babies using Tone-Pip Stimulation: A recommended test protocol, 3. Stevens, J (ed). (2002). Bone Conduction Auditory Brainstem Response Testing in Babies: A recommended test protocol, 4. Stevens, J (ed). (2009). Provisional guidelines for using Auditory Steady State Responses (ASSR) in babies: Suggested parameter values for recording frequency-specific ASSR using Natus Biologic MASTER / GSI Audera / ICS Chartr EP 200/ Interacoustics Eclipse systems, 5. Stevens, J (ed). (2002). Transient Evoked Oto-Acoustic Emission (TEOAE) Testing in Babies: A recommended test protocol, 6. Baldwin, M (ed). (2008). Tympanometry in Babies Under 6 Months: A recommended test protocol (version 2.0), 7. Williamson, T (ed). (2002). Behavioural Observation Audiometry: A recommended test protocol, 8. Day, J (ed). (2008). Visual Reinforcement Audiometry Testing of Infants: A recommended test protocol (version 2.0), In addition, significant acknowledgement is due to Ms Kelly Nichols and Ms Lisa Shannon for supplying a clinical protocol framework from which to commence. And, Ms Nuala Beahan for her efforts in co-editing several of the test protocols. 3

4 The Audiology Working Group, and in particular, Mr Ron Linning is acknowledged for the development of the Minimum Standards. Appreciation extends to Dr Joseph Kei, Dr Carlie Driscoll, and Dr Wayne Wilson for their valuable input and advice. Also to the members of the Audiology Working Group; Ms Jackie Moon, Ms Kelly Nichols, Ms Janice Wu, Mrs Sreedevi Aithal, Mr Ron Linning, Ms Suma Ajith, Ms Tania Sargent, and Ms Trang Pham. Lastly, appreciation is also extended to colleagues of the Healthy Hearing Team who have contributed in some way to the development of this document, including Ms Shirley Glennon, Ms Leanne White, Mr Gavin Bott, Ms Hayley Harpham, & Ms Nuala Beahan. 4

5 CONTENTS FOREWORD... 2 ACKNOWLEDGEMENTS... 3 CONTENTS... 5 THE HEALTHY HEARING PROGRAM AIMS AND OBJECTIVES... 8 PROGRAM AIM... 8 PROGRAM OBJECTIVES... 8 AIMS OF THE HEALTHY HEARING PROGRAM DIAGNOSTIC ASSESSMENT PROTOCOLS FOR AUDIOLOGICAL PRACTICE...10 MINIMUM STANDARDS...11 Minimum Standards Audiological Assessment of Neonates and Infants BACKGROUND INFORMATION...17 DIAGNOSTIC REFERRALS...17 SURVEILLANCE REFERRALS...17 FUTURE PROTOCOLS TO BE DEVELOPED...19 (i) Click-Evoked ABR Test Protocol SCOPE...21 PATIENT PREPARATION...21 STIMULUS...23 DATA COLLECTION AND ANALYSIS...25 CALIBRATION...29 ARTEFACTS...29 HEALTHY HEARING CLICK-EVOKED ABR QUICK SUMMARY PROCEDURE...30 QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR CLICK ABR:...31 NORMATIVE DATA...33 GLOSSARY...35 REFERENCES...36 (ii) Tone-Burst ABR Test Protocol INTRODUCTION...38 SCOPE...38 PATIENT PREPARATION...38 STIMULUS...40 DATA COLLECTION AND ANALYSIS...41 CALIBRATION...43 HEALTHY HEARING TONE BURST ABR QUICK SUMMARY PROCEDURE...45 QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR TONE BURST ABR...46 REFERENCES...47 (iii) Bone Conduction ABR Test Protocol INTRODUCTION...49 SCOPE...49 PATIENT PREPARATION...49 STIMULUS...50 DATA COLLECTION AND ANALYSIS...52 CALIBRATION...55 QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR CLICK BONE ABR:...55 USE OF TONE BURST STIMULI...56 QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR TONE BURST BONE ABR:...57 REFERENCES...57 (iv) Auditory Steady State Response Test Protocol INTRODUCTION...60 EQUIPMENT...60 STIMULUS PARAMETERS

6 CALIBRATION...63 HEADPHONES...63 HEALTHY HEARING AUDITORY STEADY STATE QUICK SUMMARY PROCEDURE...64 QUICK GUIDE: RECOMMENDED RECORDING PARAMETERS FOR ASSR...64 REFERENCES...66 (v) Transient Evoked Otoacoustic Emissions Test Protocol INTRODUCTION...68 SCOPE...68 TYPES OF OAE AND RECORDING TECHNOLOGY TEOAEs and DPOAEs...68 PRACTICAL ASPECTS...69 CRITERIA FOR DIAGNOSTIC TESTING...69 RECORDING DETAILS...71 HEALTHY HEARING TRANSIENT EVOKED OTOACOUSTIC EMISSIONS QUICK SUMMARY PROCEDURE...72 QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR TEOAEs:...73 FOOTNOTES...74 REFERENCES...74 (vi) High Frequency Tympanometry Protocol (1000 Hz) INTRODUCTION...76 SCOPE AND AIMS...76 MEASUREMENT...77 EQUIPMENT...80 TYMPANOGRAM (TRACE) INTERPRETATION...81 QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR TYMPANOMETRY...83 REFERENCES...84 TYMPANOMETRY APPENDIX...88 (viii) Behavioural Observation Audiometry INTRODUCTION...91 Aims of BOA...91 SUGGESTED PROCEDURE:...92 Test environment: Noise-maker suggestions...93 REFERENCES...96 (viii) Visual reinforcement audiometry testing of infants INTRODUCTION...99 SCOPE...99 FACILITIES & PREPARATION STIMULI TEST PROCEDURE INTERPRETATION OF RESULTS REPORTING OF RESULTS STAFF TRAINING AND EXPERTISE QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR VRA GLOSSARY REFERENCES CASE HISTORY SAMPLE QUESTIONS SUMMARY CRITERIA FOR DISHARGE FROM THE HEALTHY HEARING PROGRAM REPORTING GUIDE TO DIAGNOSING A SIGNIFICANT HEARING IMPAIRMENT (PERMANENT / CHRONIC HEARING LOSS) RECOMMENDED PRACTICES ROLE OF THE MULTI-DISCIPLINARY TEAM ROLE OF THE AUDIOLOGIST ROLE OF THE QUEENSLAND HEARING LOSS FAMILY SUPPORT FACILITATOR: HANDLING OF PATIENT FAILURE TO ATTEND AND DECLINE OF SERVICE

7 SURVEILLANCE REFERRALS- MINIMUM TEST BATTERY FOR SURVEILLANCE Monitoring the Risk of Progressive Hearing Loss: Healthy Hearing Report of PCHI not identified by the newborn hearing screen Appendix A Check list for daily and monthly function check of auditory brainstem response systems

8 THE HEALTHY HEARING PROGRAM AIMS AND OBJECTIVES PROGRAM AIM Early detection of permanent childhood hearing loss, supported by early intervention is the primary aim of the Healthy Hearing Program. Ultimately, the goal is to maximize linguistic competence and literacy development for children who are deaf or hard of hearing and this should be measured by the proportion of these children achieving linguistic skills equivalent to their non-verbal performance IQ at 3 years of age. PROGRAM OBJECTIVES The following table contains overall Healthy Hearing Program objectives, performance and outcome indicators. The objectives relevant to diagnostic audiology are highlighted. OBJECTIVE Performance Indicator Outcome Indicator 1. Optimise early detection of permanent childhood hearing impairment in neonates by providing newborn hearing screening before 3 months of age; 2. Provide diagnostic audiology assessment to relevant neonates by 6 months of age; * At least 95% of all children born in Queensland will be offered the hearing screen at birth. Rate of neonates screened per year (minimum should be no less than 95%, aim is 100% follow-up rate) Age of neonate at screening target is 3 months corrected age. Referral rate for formal audiological testing after screening per year target no greater than 4%. Ideally around 2-3%. * Minimise false positives - target <4% and false negatives - target is zero.. * Begin diagnostic audiological assessment by 2 weeks following refer for bilateral refers and 6 weeks unilateral. 1-2 children per thousand with a bilateral sensorineural hearing loss >40dBl detected before 3 months. * Rate of neonates offered the hearing screen. Currently - to end of >98% * Rate of neonates who are screened. Currently - to end % *Proportion of all infants screened by 3 months. Proportion screened by 6 months. Currently - average age at screening - 40 wks * Rate of neonates referred to audiology directly from screening and from targeted surveillance. Currently - to end Direct Refers % and Targeted Surveillance % *Total no & percentage of neonates tested false-positive and/or false-negative. *Total number and percentage of neonates beginning assessment within timeframes. * Rate of neonates diagnosed by 3 months. 8

9 3. Ensure equitable access to the Healthy Hearing Program for all neonates irrespective of social, economic, cultural or geographic circumstances; 4. Ensure the Healthy Hearing Program is standardised and provided using multidisciplinary, evidence based screening, diagnostic, treatment and habilitation protocols; 5. Provide maintenance care for all children who have a cochlear implant at the time of the commencement of the Healthy Hearing Program; 6. Provide an outreach hearing diagnostic and treatment service in the Cape York and Torres Strait region for children from an Aboriginal or Torres * 95% of neonates referred from the Healthy Hearing Program will be diagnosed and referred to Australian Hearing and/or Cochlear Implant Program by 6 months or 12 months Corrected Age, respectively. * Percentage of neonates diagnosed and referred to Australian Hearing and/or Cochlear Implant Program by 6 months or 12 months Corrected Age, respectively. * See above * See above * Appropriate resources for Indigenous and * Proportion of infants from Indigenous non-english speaking families are and non-english speaking background available. offered and participating in screening is * Support for rural and remote families is comparable to representation in available and offered. population. * Benchmarking - National and * All screening indicators comparable International Standards - eg: SCREENING: with national and international best First Refer rates, Second Refer rates, practice. Capture rate, Targeted Surveillance rates. * Audit and quality processes in place for *AUDIOLOGY: see above + 1-2/1000 all program components. SNHL detected * Children with hearing loss appropriately * Development Diagnostic Assessment identified. Protocols for Audiological Practice * Diagnostic Assessment for Audiological Practice developed and * TREATMENT & HABILITATION: implemented. Literature Review on Early Intervention for * Literature Review finalised and made children with a Hearing Loss to be available to all program and early undertaken. intervention services. * All children with CI who are managed through the Mater or RCH CI program have access to maintenance services. *Average age at intervention - Cochlear * Audit of CI children s access to Implant target is 12 months corrected age maintenance services. (or clinically appropriate). * Age at implantation. * Managed by Royal Childrens Hospital * Managed by Royal Childrens Hospital and Cairns Hospital and Cairns Hospital 9

10 Strait Island background. AIMS OF THE HEALTHY HEARING PROGRAM DIAGNOSTIC ASSESSMENT PROTOCOLS FOR AUDIOLOGICAL PRACTICE 1. To ensure effective, efficient and accurate diagnosis of Permanent Childhood Hearing Loss (PCHI) for children referred from the Healthy Hearing Program, either at birth or for surveillance at later ages. 2. To ensure consistency and equity of access to high quality diagnostic services throughout the state. 3. To ensure diagnostic procedures are evidence-based and reflect best practice for diagnostic audiological assessment for neonates and infants. 4. To provide the basis for: Consistent and accurate information gathering for program reporting and evaluation purposes; Service Level Agreements with districts; Contracting with private paediatric diagnostic audiology services. Training and credentialing of all Paediatric Diagnostic Audiologists and New Graduates. At the time of this document s preparation there were no schemes in place to train Audiologists in the area of Paediatric Diagnostic Audiology. It was, however, recognised that a new graduate or inexperienced Audiologist was unable to practice competently in the area without significant supervision. For this reason, Audiologist s wishing to practice in the area of Paediatric Diagnostic Audiology under the auspices of the Healthy Hearing Program must have demonstrated a significant period (2 years) of paediatric diagnostic audiology experience. Should an Audiologist not meet this period of practice then they will be required to undergo a training and mentorship program with an experienced Paediatric Audiologist. All Audiologists will be required to complete the Healthy Hearing Diagnostic Assessment Protocols for Audiological Practice (DAPAP) training to be able to practice paediatric diagnostic audiology for the Healthy Hearing Program. As the DAPAP will be a constantly evolving document refresher courses will be required every two years. A specific program of credentialing will be developed to accompany these training requirements. 10

11 MINIMUM STANDARDS Background At the outset of the Healthy Hearing program a set of minimum audiology practice standards were developed. The minimum standards were devised according to the level of care provided at that facility (level 1, level 2 and level 3 or tertiary). The minimum standards initially served as a guideline for Audiological Practice in the assessment of neonates and babies. However, as the Healthy Hearing Program progressed it was recognised that these standards did not provide the significant detail required for a quality program in Audiology practice and assessment. Consequently, the minimum standards have served as a basis for development of this document. They are included in this document for background purposes only and are no longer recognised as the minimum standard of assessment. This document replaces the minimum standards and all facilities are now required to follow the same assessment protocol. It is acknowledged that new or developing sites (eg. in remote or rural areas, or new hospitals) may not meet the protocol due to equipment or resource limitations. This will be rare, negotiated with the State-wide Director of Healthy Hearing and always precede referral to a site that can complete the audiological assessment according to protocol. 11

12 Minimum Standards Audiological Assessment of Neonates and Infants Entry at any level as clinically appropriate (i.e. Level 1, 2, 3 not necessarily sequential) Referral between levels as appropriate eg may be diagnosed with AN in 3 and then return to level 2 for monitoring Facility Role/Requirements Comment Capacity Skills/Resources Equipment Appropriate Patient (Example) Level I Minimum requirements for Level 1assessment: (Replaces or validates screening procedure) Minimum PASS requirements: A. Click evoked ABR - Pass = Wave V present down to 30 dbnhl bilaterally, and Waves I, III and V identifiable at suprathreshold levels B. OAE - Pass = S/N ratio 6dB or more in 3 frequency bands across the 1 4 K khz range To evaluate if the baby has functionally normal hearing bilaterally. To report to Healthy Hearing Program using appropriate format. To appropriately refer on as clinically indicated. Proforma for standardised reporting to be drafted. Including contact details of Healthy Hearing, place for parents to sign for release of information, place for parents to sign to say they have been told and understand results and next steps required Administer, interpret and report on results obtained in audiological assessment of neonates and infants with ABR, high frequency tympanometry and otoacoustic emissions. To appropriately report results to parent/carers. Limited access to facilities to establish threshold across the speech spectrum Some experience is providing parents regarding diagnosis of hearing loss in neonates Auditory Brainstem Audiometry (ABR) air and bone conduction (click) Diagnostic Otoacoustic emissions Access to some basic behavioural measures of responsiveness to sound i.e. noise makers First audiological assessment after a double refer from screening. Baby back transferred home prior to screening were local screening in not available or not appropriate. 12

13 Facility Role/Requirements Comment Capacity Skills/Resources Equipment Appropriate Patient (Example) Level II If a baby does not PASS: In addition to level 1 skills: In addition to level 1 equipment: Minimum requirements for Level II assessment (minimum standard) Essential: A. Click ABR Air conduction bilaterally to threshold levels. B. Click ABR Bone conduction. C. Frequency specific measure ASSR or tone burst at 1 KHz showing threshold for sensorineural losses. Desirable: A. Waves I, III and V seen at suprathreshold levels B. High frequency Tympanometry. C. Ipsilateral reflex D. Additional frequency specific information obtained E. Frequency specific measure ASSR or tone burst at 1 To obtain site of lesion information. To establish threshold estimates across the major speech frequencies bilaterally. To appropriately support families through the diagnosis of a hearing loss. To link families to services according to Healthy Hearing clinical pathways. To appropriately report to Healthy Hearing Program. A list of information to be routinely covered in informational counselling is required. This will assist to standardise information and to support less experiences audiologists. More discussion required regarding management of each possible outcome of this level i.e. pass, conductive, sensorineural hearing loss More definition and standardisation is required regarding noise makers and use of these + Administer, interpret and report on results obtained in the audiological assessment of neonates and infants with: behavioural observation audiometry, frequency specific electrophysiological measures of hearing sensitivity, cochlear microphonic. + To provide appropriate information to families in a timely, appropriate and unbiased manner + Demonstrated experience in providing informational counselling to parents regarding diagnosis of significant hearing loss - Does not require access to tertiary level audiological or medical facilities such as sedation, cochlear implant programs High frequency tympanometry Frequency specific electrophysiologica l equipment e.g. auditory steady state response, tone burst ABR Facilities for appropriate behaviour assessments including VROA and noise makers Optional: Noise makers and sound level meter or a standardised generator (more definition required) Any baby where the initial audiological results were not WNL. Confirmation of hearing loss. Monitoring of conductive hearing loss. Surveillance of healthy hearing babies Initial assessment for baby with high likelihood of hearing loss would be recommended to occur in this setting eg syndrome with known risk of hearing loss, strong family history. 13

14 Facility Role/Requirements Comment Capacity Skills/Resources Equipment Appropriate Patient (Example) KHz showing threshold for conductive losses. Level III In addition to level 1 and 2 level skills: In addition to level 1 and 2 level equipment: Audiological minimum standards as per level I for PASS and level II for further assessment Tertiary level (i.e. hospital setting) Experience in management of medically and developmentally complex paediatric population Capacity for procedures such as sedation, cochlear implants etc Access to multidisciplinary team and tertiary level medical management eg ENT Baby with complex audiological, social or medical presentation. Profound SNHL Auditory neuropathy. All permanent SNHL for access to hearing impairment clinics. 14

15 Facility Role/Requirements Comment Capacity Skills/Resources Equipment Appropriate Patient (Example) Surveillance Centres Minimum requirements for Surveillance assessment: Separate information across the speech frequencies obtained by VROA with insert headphones or OAEs. Pass = VROA thresholds db SPL 25 at 0.5 khz 20 at 1, 2 and 4 khz AND To provide monitoring of babies identified as at risk of progressive hearing loss To provide follow-up for babies referred back into the system eg parent concern Aim is to provide separate ear information across the major speech frequencies Reporting - Will the template allow for reporting of this population? Referral pathways if loss identified One adequately trained and experienced audiologist Available support personnel as required. Administer, interpret and report on results obtained in the audiological assessment. Essential: VROA facilities (Optional with B/C and separate ear capabilities) Tympanometry Otoacoustic emissions Parent concern GP concern Identified by Healthy Hearing as requiring surveillance Identified by audiologist as requiring surveillance OAE Present with S/N ratio 6 db or greater across three frequencies across 1 4 khz range And 15

16 Facility Role/Requirements Comment Capacity Skills/Resources Equipment Appropriate Patient (Example) Middle Ear Analysis 16

17 THE HEALTHY HEARING PROGRAM AND AUDIOLOGY BACKGROUND INFORMATION The aim of Audiology within the Healthy Hearing Program is to identify hearing loss which may impact on a child's speech and language development. There are two streams to the Program Diagnostic and Surveillance; DIAGNOSTIC REFERRALS Children referred to the Audiology Department from the Healthy Hearing Program who have had their hearing screened in the nursery using AABR and referred twice (either unilaterally or bilaterally), or have been referred directly due to factors that make them unsuitable for screening (eg. atresia, craniofacial abnormalities) All bilateral refers from the screening AABR are aimed to be seen for Audiological assessment within 2 weeks from the date of the referral, provided the infant is medically stable. All unilateral refers from the screening AABR are aimed to be seen for Audiological assessment within 6 weeks from the date of referral, provided the infant is medically stable. SURVEILLANCE REFERRALS Children referred from the Healthy Hearing Program who have passed screening bilaterally, but have had High Risk Indicators identified in their medical history, placing them at risk for progressive or late onset hearing loss. See the Surveillance referral pathway to determine audiological assessment timeframes. 17

18 (1) DIAGNOSTIC REFERRALS- The Minimum Test Battery The minimum requirements, for discharge with normal hearing, when assessing a baby referred from screening include the following assessments on BOTH ears; (a) Click-evoked ABR (assesses broad spectrum, but is most sensitive in the 2-4 khz Regions). (b) Assessment of hearing at 1 and 4 khz must include one of the following; Option 1: Tone burst ABR. Option 2: ASSR. Option 3: TEOAE testing (1-1.5 and 4 khz). (c) High Frequency Tympanometry (1000 Hz probe tone). A baby is required to have normal test results in all of the above assessments prior to discharge. A baby suspected of a having a hearing impairment is required to repeat the click-evoked ABR, in addition, the following will also be performed; (d) Bone conduction ABR. (e) Toneburst ABR across the frequency spectrum, or ASSR testing across the frequency spectrum. Frequency specific information is required for referral to Australian Hearing and reasonable access to rehabilitation. The following sections contain test protocols for all assessments that may be conducted throughout the course of Audiological assessment appointments; (i) Click-evoked Auditory Brainstem Response Test (Click ABR) (ii) Tone-burst Auditory Brainstem Response Test (Tone-burst ABR) (iii) Bone Conduction Auditory Brainstem Response Test (BC ABR) (iv) Auditory Steady State Evoked Potentials (ASSRs) (also known as Steady State Evoked Potentials, SSEPs) (v) Transient Evoked Otoacoustic Emissions (TEOAEs) (vi) High Frequency (1000Hz Probe Tone) Tympanometry (vii) Behavioural Observation Audiometry (BOA) (viii) Visual Reinforcement Audiometry (VRA) 18

19 All measures should be undertaken to adhere to the test protocols. In extraordinary circumstances, deviation may occur. In this instance, the clinician is required to use appropriate clinical decision making before doing so, document the circumstances, and keep records regarding the deviation. The above tests do not exclude the ability to use additional tests, such as; (a) Distortion Product Otoacoustic Emissions (b) Acoustic Reflex Testing The use of these tests is highly encouraged, to provide additional clinical information. They may be performed at the clinician s discretion but are not mandatory. FUTURE PROTOCOLS TO BE DEVELOPED It is envisaged that a protocol regarding Auditory Neuropathy Spectrum Disorder will be inserted into this document in the near future. Protocols for DPOAE testing and Acoustic reflex testing will also be developed in future versions of the protocol. 19

20 Click-Evoked ABR (i) Click-Evoked ABR Test Protocol Air-conduction Auditory Brainstem Response testing in babies using clicks- A Recommended Test Protocol 20

21 Click-Evoked ABR (i) Click-Evoked ABR Test Protocol Air-conduction Auditory Brainstem Response testing in babies using clicks- A Recommended Test Protocol SCOPE The ABR Protocol aims to provide guidelines for testing babies in the first few months of life by ABR using click stimuli for the purposes of assessing hearing sensitivity. Tone burst ABR and bone conduction ABR are covered in separate documents. Clicks are currently employed for newborn hearing screening. For diagnostic assessment of hearing impairment, further frequencyspecific information is required, obtained by the use of tone burst ABR or auditory steady state responses. The document covers the technical procedure of carrying out an ABR test and the reporting of the results. It does not cover practical aspects such as handling of the baby or criteria to be used to decide whether a baby has passed or failed an ABR screen. Equipment that carries out automatic ABR is available and is used in newborn hearing screening only. The test protocol in this type of equipment is usually fixed. This document refers to diagnostic ABR (i.e. non automated) ABR. Any changes in this protocol should be performed with careful consideration and with appropriate clinical justification. PATIENT PREPARATION Precautions against cross infection Local procedures should be adhered to, including the handling of infections such as MRSA. Suggested minimum practice is that all equipment other than the electrodes, preamplifier and earphone should remain outside the baby s cot or, when the baby is not in a cot, should be placed at a distance from the baby. Any item in the cot that is likely to come into contact with the baby should be cleaned, using a suitable method, before being used on another baby. Electrodes are dealt with under the next section. The earphones and electrode leads should be cleaned with soap and water or swabbed down with alcohol gel. Testers should wash their hands thoroughly before and after handling the baby and make use of alcohol gel as prescribed by local infection control procedures. It is recommended that local advice is sought regarding infection control methods. 21

22 Click-Evoked ABR Choice of electrodes and application Disposable electrode tabs should be used at all times, this minimises contact of the electrode leads with the baby. It is recommended that disposable electrodes are used to facilitate sterility. It is important to devise a sterile procedure and the following is recommended if disposable electrode tabs are not used. The skin should be carefully abraded by using a suitable sterile abrasive electrode paste and clean gauze. If non disposable electrodes are being used, the electrodes, after cleaning, should be placed in a solution such as chlorhexidine solution to disinfect them. However this does not sterilise the electrodes and local advice should be sought on effective sterile procedures. The International Organisation of Societies for Electrophysiological Technology (OSET) has published useful guidelines on the prevention of infection in electrophysiological procedures 2. The amplitude of any artefact resulting from induced electrical interference is proportional to the difference in the electrode impedances. A low value for the difference in impedances is most easily obtained by ensuring all electrodes have low impedances. The impedance, as measured between each electrode pair, should be in the range 1000 to 5000 ohms. Although in good recording conditions and in a screened room higher electrode impedances can be tolerated, it has been found that on a Special Care Baby Unit, values below 5000 ohms are normally necessary to reduce mains (50Hz) interference to an acceptable level. At high stimulus levels a high electrode impedance would also give an unacceptably large stimulus artefact which would obscure the initial part of the response and may activate the data rejection facility so that no data are averaged. Electrode location One channel or two channel recording can be used. In single channel recording, electrodes are located as follows: Negative electrode: ipsilateral mastoid or nape of neck. If using mastoid, use a low mastoid position unless wishing to record the post-auricular myogenic response. Positive electrode: high forehead as near as possible to Cz a and midline. The fontanelle should be avoided but the electrode should be placed as close as possible to this otherwise the ABR response will be reduced in size. 22

23 Click-Evoked ABR Common electrode: contralateral mastoid when using the ipsilateral mastoid electrode for the negative electrode. If the nape of the neck is used for the negative electrode, the common electrode can be placed on the forehead (at least 4cm from the positive electrode) or either mastoid, whichever is the more practical in the individual case. The above electrode configuration should result in wave V being plotted upwards on the display. If this is not the case then the positive and negative electrode connections should be reversed. There is some evidence that the nape of the neck rather than the mastoid gives a larger wave V response although the signal to noise ratio may not be any higher. However if wave I is required (for neuro-diagnostic purposes) the mastoid should be used. There is a slight increase in the amplitude of the response if the positive electrode is placed nearer to the vertex position (Cz) a. In Two channel recording, electrodes are located as follows: Negative electrode: ipsi-lateral mastoid and contralateral mastoid. Positive electrode: high forehead as near to Cz as possible, avoiding the fontanelle. Common electrode: forehead. Contralateral electrodes will be used in the two channel recording. Note that if bone conduction ABR is also to be carried out this may influence the choice of the electrode placement for air conduction ABR. If the option of two channel BC ABR recording is being considered then the common electrode can be placed on the forehead as the ipsilateral and Cz a is the standard position used in adults. It is defined in the electrode system for electroencephalography. For the purpose here it can be taken as the point along the midline of scalp half way between the bridge of the nose (nasion) and the start of the skull at the rear of the head (inion). STIMULUS Stimulus and stimulus rate An electrical click of 100μs at a stimulus rate of around 22.1 per second is recommended, with alternating polarity to minimise stimulus artefact. A figure such as 22.1/s, which does not have a common factor with mains frequency, should be chosen to minimise any mains artefact. A check should be made that the stimulus rate allows the data collection to be completed prior to the next 23

24 Click-Evoked ABR stimulus being given. This can be checked by timing the collection of 1000 sweeps and confirming that the time taken is = (1000 stimulus rate). The level of stimulus output should be monitored by listening to the earphone at critical points during the test. Stimulus levels should be recorded in dbnhl. The nhl can be taken to imply the use of either ISO (2007)3, NHSP-recommended calibration values 4, or other calibration datum that is referenced to the average psycho-acoustic threshold of a group of normally hearing young adults. For testing carried out under the Healthy Hearing Program, the advice in the NHSP assessment guidelines should be adhered to. The relevant text is: Note that the polarity of the stimulus can affect the response waveform and in cases of ANSD it may be useful to record responses to both rarefaction and condensation clicks. The majority view, based on current practice, was that for newborn hearing screening and threshold measurement alternating polarity should be used to minimise the stimulus artefact. The stimulus presentation should occur at 70, 50, and 30 dbnhl as a minimum for both ears. Two traces at each level are required. Should a hearing impairment be suspected, then clinical threshold seeking is required, with a minimum of two waveform required at threshold. Earphone This should be of sufficient quality to deliver a stimulus up to 140 dbspl peak (about 107 dbnhl) without distortion. TDH39/49 headphones are recommended. However, insert earphones (e.g. type EAR-3A) may be used. Calibration may be more difficult with insert earphones due to greater variation in enclosed volume. However, insert earphones reduce the need for masking. If insert earphones are used, care should be exercised that wax is not compacted by the probe, so blocking the sound pathway. Care should also be taken to ensure that the method of insertion is standardised (eg 3 mm marked on the insert tubing). Earphones should be centred over the ear canal ensuring that the ear canal is not collapsed due to excess pressure. 24

25 Click-Evoked ABR Warning insert earphones If insert phones are used in babies, the recommendation is that they should not be used above 85 dbnhl unless they include a microphone to automatically adjust the stimulus level for ear canal volume. The reason for this is that a baby has a much smaller ear canal which can give up to about a 20 db rise in the stimulus level compared to the same insert earphone used in an adult (Voss & Herrman, 2005; Rance & Tomlin, 2006; Sininger et al, 1997). This figure is thought to diminish over the early months of life as the ear canal grows. In view of the evidence suggesting that insert earphones giver higher stimulus levels the following provisional values are proposed by the NHSP. These values MUST be added to the stimulus level in dbnhl to correct for the effect of the smaller ear canal volume in babies less than 3 months of age in comparison to adults. Hence, if performing a click-evoked ABR and a threshold of 20 dbnhl is obtained, that threshold is to be corrected to 30 dbnhl (as per the table below). Table 1. Provisional correction to insert earphone stimulus level for the effect of the smaller baby ear canal volume. Click 500Hz 1000Hz 2000Hz 4000Hz The application of the insert headphone correction factors will be updated as appropriate in future versions of this protocol pending developments of research in this area, and the findings of the Healthy Hearing Audiology working group. DATA COLLECTION AND ANALYSIS Amplifier and artefact rejection level The sensitivity/gain should be set such that any electrical activity greater than about ± 10μV is rejected. Some users have found that lower rejection levels down to ± 5μV are better. A value of between ± 5μV and ± 10μV is therefore recommended. The equipment manuals should be checked to determine what value of amplifier sensitivity is required to achieve these rejection levels. 25

26 Click-Evoked ABR The use of higher rejection levels is not recommended when recording conditions are difficult (e.g. high muscle activity). The result is likely to be a poorer signal to noise ratio in the averaged signal. Babies need to be sleeping or in a very settled state when testing. Filters Low frequency (high pass): A value between 20 to 100 Hz is recommended. A value between 20 to 30 Hz has been found to give the best signal to noise ratio of wave V near threshold. High frequency (low pass): A value around 1500 Hz is recommended. There is little response energy above this frequency. A higher value generally adds more electronic noise from the amplifier. Notch filter Under normal recording conditions this will not be required as 50 Hz mains artefact should be absent or minimal with good electrode practice using current equipment. If mains artefact levels are high it is better to identify and remove the source of the problem rather than use a notch filter which can introduce distortion. Window length and Averaging The longest response acquisition window consistent with the chosen stimulus rate should be used. This will normally be less than 15 ms (see section on stimulus rate above). The number of sweeps per replication accepted by the averager should be varied depending on both the size of the response and the level of background activity. It will normally vary between about 1200 and 2000 sweeps, although higher numbers will be required when the responses are small or the background noise is high. Typically a figure of 2000 sweeps is recommended with a minimum of Exceptionally there may be such a large ABR response or low background activity that fewer sweeps can be used. The number of rejected sweeps will depend on the level of background activity and the rejection level that has been chosen. Whenever the electrical activity from the baby exceeds the rejection levels for long periods of time data collection must be halted until the baby has settled for the reason given below. Recordings made where there is a high number of rejected sweeps must be treated with caution. Do not widen the reject levels in an attempt to complete testing on an unsettled baby. 26

27 Click-Evoked ABR Data rejection facilities on current equipment are effective in rejecting most unwanted sweeps. However, when there is a long period of high background activity and the data collection is not interrupted there will be a greater proportion of sweeps containing higher levels of noise added to the averaged response. Display The convention of plotting wave V upwards is proposed as it is the most common in current practice. It is recommended that the display be always set at a fixed number of μv/division. The amplitude (y) and time (x) scales should be such to ensure that small waveforms near threshold are visible. It is recommended that 0.1μV on the response amplitude (y) axis is the same size on the display as 1 2 ms on the time (x) axis. It is also recommended that the same display scales are used for all tests. An automatic display gain must not be used as an inappropriate gain for assessment of the response may be set. Criteria for accepting the presence of a response and establishing the ABR threshold For most current ERA recording systems acceptance of the presence of a response depends on visual interpretation. Replication of responses (as defined below) is therefore essential if a correct visual interpretation is to be made. The only exception to this should be where the result is not used in the determination of threshold. For example, if the first stimulus level is 50 dbnhl and a flat trace is obtained then the best use of time may be not to replicate until a response is observed at higher stimulus levels and it is clear which levels need to be replicated to determine threshold. For an infant suspected of having hearing impairment, there should be a minimum of a replicated response at threshold, at 10 db or 5 db below and at 10 db or 5 db above threshold. The exception to this is where a clear response is obtained at the recommended Healthy Hearing discharge level of 30 db nhl. In this situation a replicated response at 30 db nhl is sufficient. For each stimulus level the result should be marked in one of three ways. (a) response present, (b) good recording conditions but no response was recordable or, (c) recording conditions too poor to establish a result. 27

28 Click-Evoked ABR For each stimulus level the result should be marked in one of three ways. (a) response present, (b) good recording conditions but no response was recordable or (c) recording conditions too poor to establish a result. For (a) there must be a high degree of correlation between the replications and a characteristic waveform. For (b) the replications must be low in amplitude (peak to peak below about 0.05μV) with no significant correlation and for (c) the replications will have amplitudes above about 0.05μV peak to peak without a high degree of correlation. Where condition (a) is not met and there is some evidence of a response further replication may be able to determine whether a response is present or not. For example, two further replications could be carried out and the replications could be added in pairs to produce two summed traces, each the average of a higher number of sweeps. In any decision, all recorded traces at each stimulus level should be considered and only those rejected where there is a good technical reason or where the noise levels (e.g. electro-myogenic activity) were high. Results should clearly be marked as to whether they are threshold or the lowest level tested. It should also be made clear in the results when threshold measurement was not possible due to the maximum stimulus limits of the equipment. A useful convention (used on esp) is to use = for threshold, for lowest level tested (where the threshold may be lower) and > for threshold above maximum level tested. So for example 35dBnHL would mean a clear response (condition a) at 35dBnHL but not tested below this level and >80dBnHL would mean no response (condition b) at 80dBnHL but not tested above this level. At the completion of the ABR appointment, all traces MUST be reviewed by a peer and cosigned regarding the agreement of interpretation. The co-signer should have a minimum o two years of paediatric ABR experience. This process MUST occur regardless of the institutional setting and the degree of experience of the Audiologist. Should an Audiologist work as a sole practitioner, then the Healthy Hearing Program will ensure that that Audiologist is linked to a peer reviewer to verify all ABR traces. Traces MUST be peer-reviewed and co-signed prior to the completion/distribution of the diagnostic report. Definition of ABR threshold for Healthy Hearing The ABR threshold has been defined in the NHSP assessment guidelines 1 as the lowest level at which a clear response is present, with the absence of a recordable response at a level 5 or 10dB 28

29 Click-Evoked ABR below the threshold, obtained under good recording conditions. This definition will be adopted for the Healthy Hearing Protocol. The ABR wave latencies will be compared to the normative data established by Jacobsen & Morehouse (1984). Wave latencies that fall outside the normative data should be reported as abnormal. Furthermore, the interaural latency difference should be no greater than 0.3 ms. CALIBRATION A Stage A check should be carried out on the ERA equipment prior to use. Details of this are available in Appendix A. ISO (2007) provides reference equivalent threshold sound pressure levels (RETSPL) for click and tone burst stimuli used for AC ABR for certain types of transducer. It also provides a standard for reference equivalent threshold force levels (RETFL) for use for click BC ABR for the B71 type bone vibrator. However there are no RETFLs for tone burst BC ABR. A procedure for calibration is given in IEC (2007)5. In July 2005, a provisional set of reference levels for AC and BC ABR was agreed for the NHSP: and the latest version of these figures is published on the NHSP website 4, with the ISO389-6 values used where appropriate. These values should be used to calibrate equipment used for hearing assessment. It is important to note that the stimulus rate will affect the psycho-acoustic threshold but not the ABR threshold 6. When performing a subjective (stage A) listening check therefore, the use of the recommended stimulus rate near 50 per second will make the clicks sound about 3 db too loud. Bear this in mind or perform the listening check at 20 per second. It is important that the physical intensity of the stimulus does not change as the stimulus repetition rate is changed since this can introduce errors. This is difficult to detect subjectively and NHSP can advise which instruments require users to apply a correction for this problem. ARTEFACTS Recording system checks The equipment should be checked at regular intervals (monthly is recommended) for system artefacts. This applies not only to click ABR but to all the protocols for auditory evoked potentials. Using the normal protocol for testing, connect the electrodes together. Run the normal protocol twice and check that a flat trace is obtained with a minimal level of residual system noise (peakto-peak below 0.05μV) and no correlation between repetitions. 29

30 Click-Evoked ABR At regular intervals (monthly is recommended), when testing a baby, carry out an additional control recording to check that there are no artefacts in the recording. Do this on a baby where a clear ABR response has been obtained. Block the sound from reaching the ear and repeat the test with the stimulus still on. This can be achieved by covering the earphone or by sealing the insert earphone tube (ensure that the sound is not audible). A flat trace should be obtained with a minimal level of residual EEG (peak-to-peak below 0.05μV for a quiet baby) and no correlation between repetitions. Control recordings when testing babies It is also recommended that a control recording is carried out with the stimulus acoustically blocked whenever the ABR response is marginal and/or is of the form that could be an artefactual response: e.g. in tone burst ABR it is often the case that only wave V and SN 10 are observed. Mains artefact could produce a similar response. If the response is artefactual and is not an electro-physiological response to the sound stimulus it will still be present when the stimulus is acoustically blocked. Note that marginal responses, that do not take the form of a potential artefact, may not need to be checked if well supported by clear repeatable responses at 5 or 10dB higher stimulus levels. Action required If artefactual responses are observed, then it is essential to determine their source and remove them from the recording process. Advice should be sought and if necessary manufacturers contacted, so that the source of the artefacts can be eliminated. REPORTING NOTE: Please be aware that Australian Hearing may apply correction factors to convert ABR thresholds to estimated hearing thresholds (db ehl) suitable to be used for hearing aid fitting. Australian Hearing conversions are based upon ABR thresholds being reported in db nhl. Healthy Hearing diagnostic audiology reports should state which decibel scale is being reported, and any correction or calibration factors applied to the thresholds in addition to those covered in this document. HEALTHY HEARING CLICK-EVOKED ABR QUICK SUMMARY PROCEDURE 30

31 Click-Evoked ABR - Both left and right ears must be tested, regardless of whether the infant has a bilateral or unilateral refer. - Testing is routinely carried out at 70, 50 and 30 dbnhl, and at least 2 traces, at each test level, are required. Clinical judgement and threshold seeking is required if waves are not identifiable at these levels. - A child is deemed to have functionally normal hearing if a repeatable wave V is seen down to 30 dbnhl. - Major wave components (I, III and V) should be present at suprathreshold levels (70dB nhl or higher as necessary). - A latency intensity function for the absolute latency of wave V is to be plotted and compared to age appropriate norms 7. - The central transmission time at supra-threshold level (i.e. 70dB nhl) should be compared between ears for symmetry (significant asymmetry = interaural latency difference > 0.3 msec). QUICK GUIDE: RECOMMENDED PARAMETERS AND SETTINGS FOR CLICK ABR: Electrode Location: One Channel: Positive: High forehead/vertex Negative: (i) Ipsilateral mastoid or (ii) nape Common: (i) Contralateral mastoid or (ii) forehead/mastoid Two Channel: Negative electrode: ipsi-lateral mastoid and contralateral mastoid. Positive electrode: high forehead as near to Cz as possible, avoiding the fontanelle. Common electrode: forehead. Contralateral electrodes will be used in the two channel recording. Stimulus: Alternating polarity click*: Rate 22.1 to 33.1/s + 31

32 Click-Evoked ABR Stimulus presentation level: 2 traces required at 70, 50 and 30 dbnhl as a minimum for normal discharge. Clinical threshold seeking required if loss is suspected. Earphone: TDH39/49 preferably (testing down to 30 db) EAR-3A or insert earphones with correction factors (testing down to 20 db to include correction factor) Coupler value for 0dBnHL: Amplifier reject levels: Filters: Refer to NHSP calibration data 4 ±5 to ± 10 uv Low frequency: Hz High frequency: 1500 Hz Window length: Number sweeps averaged per replication : Display: 15 ms maximum Minimum 1200 Typically μv on amplitude axis = 1 2ms on time axis * refer to section on stimulus and stimulus rate. +And deviations from the recommended rate should have a documented reason for deviation. 32