Evaluation of Transient Evoked Otoacoustic Emission in the Newborn Hearing Screening Program in Neonatal Intensive Care Unit

Abstract

Introduction Newborn hearing screening (NHS) program has been implemented to include not only babies with identifiable risk factors for permanent hearing loss but all babies admitted in the wellbaby nursery and neonatal intensive care unit (NICU) in Korea. Evidence to support the expansion of the NHS program continues to collect. Early identification of hearing loss and appropriate intervention aims to assure adequate opportunity to maximize language development and communication for children with hearing loss.1,2)Accurate audiological evaluation of hearing in young babies requires appropriate technology and experienced manpower. For screening purposes, the screening tests should have acceptable range of sensitivity and specificity, and yet be easy to handle for use by various personnel. Automated auditory brainstem response (A-ABR) and otoacoustic emission (OAE) tests are considered as methods of choice for NHS.1) NHS protocols may vary in the choice of the tests and the number of repeated screening tests ("stages") among different institutions.3,4) In the early days of NHS, the test method was recommended to be selected from either OAE or auditory brainstem response (ABR) or both.5,6) Both ABR and OAE tests can identify sensory/cochlear) hearing loss. However, OAE responses may be intact in cases of neural hearing loss (auditory neuropathy/auditory dyssynchrony), that would be identifiable by abnormality in ABR. Since the babies admitted in NICU are more likely to be at risk for neural hearing loss than their counterpart in wellbaby nursery, the current recommendation for NHS testing methods are different for each group. The 2007 position statement of the Joint Committee on Infant Hearing (JCIH) updated the recommendation for test protocols: A-ABR is recommended if a single test method is chosen for screening of NICU babies.1)The aim of this study is to present the outcome of NHS using transient evoked otoacoustic emission (TEOAE) as initial evaluation method in NICU graduates to discuss the necessity of ABR to complement its limitation. Subjects and Methods The clinical data of all babies who were admitted in NICU at the Yonsei University College of Medicine Gangnam Severance Hospital between February 2010 and November 2011 was retrospectively reviewed. All babies were screening using a two-staged NHS program (Fig. 1). TEOAE tests were performed as initial screening method within 2-5 days from birth. If the babies "failed" the initial TEOAE screening, otoscopic examination and second stage TEOAE tests were performed. After the two stages of TEOAE, referred babies were recommended for diagnostic audiological evaluation including ABR. Referral rates were estimated and quality indicators for screening recommended in JCIH 20071) were evaluated. Two qualified audiologists performed testing of neonates. All neonates were screened for hearing impairment using TEOAE within 5days after birth before discharge from the hospital. TEOAEs were recorded using ILO 92 Otodynamics analyzer system (Otodynamics, England, UK) and ILO V6 software. The tests were performed in soundproof audiobooths. A click stimulus with 80 μs duration was presented at a repetition interval of 20 msec. TEOAEs were considered present ("pass") if the signal-to-noise ratio was 6 dB or great in at least 3 of 5 frequency bands, and absent ("fail" or "refer") otherwise. Results During the study period, 149 neonates graduated from NICU and all underwent hearing screening. Initial TEOAE tests were performed within 2-5 days after birth. Fifty out of 149 (33.6%) babies were scheduled for second stage program. However, 9/50 of them were lost to follow up. From initial screening, TEOAEs were absent unilaterally in 33/50 (66.0%) babies, and bilaterally in 17/50 (34.0%)(Fig. 2). In the second stage screening using repeated TEOAE was performed within 1 month of birth, 35/41 (85.4%) babies were "passed" and 6/41 (14.6%) remained "fail" cases. From the two-staged NHS protocol, 6/149 (4.0%) of total NICU babies tested were referred for diagnostic audiological evaluation: the "failed" results were bilateral for 2 babies and unilateral for the remaining 4 babies (Fig. 2). TEOAE or ABR tests were recommended for the 6 referred babies, but 3 were lost to follow up visits. Two babies underwent otoscopic examination, tympanometry and TEOAE and were cleared for all tests. ABR test was performed on one referred baby to reveal profound hearing loss in both ears. Almost of all babies that passed NHS from either the initial or second stage TEOAEs did not present for further evaluation. However, one baby that initially failed TEOAE but later passed the second stage test returned for audiological evaluation at 3 months of age, following our recommendation bases on the prenatal history of syphilis infection. TEOAEs were still present, but the ABR test revealed hearing thresholds of 50 dBnHL in the right ear and 30 dBnHL in the left. He is scheduled for regular follow up tests. As for any screening programs, regular monitoring and quality control are required for NHS programs. We evaluated the results of our NHS program using TEOAE in NICU patients by estimating quality indicators for screening as recommended in JCIH statement.1) First, the percentage of all newborn infants who complete screening by 1 month of age was estimated as 94.0% (140/149) for NICU graduates. Second, the percentage of all newborn infants who fail initial screening and fail any subsequent rescreening before comprehensive audiological evaluation is 4.0% (6/149) for our NICU babies. Discussion Hearing loss is a common congenital condition, occurring in approximately 0.1% of the normal population, and can result in detrimental effect on speech and language development in children without early intervention.2) NHS program was initiated for early detection of hearing loss in infants and encompasses identification of hearing loss soon after birth, persistent follow up evaluation of hearing and language development, and appropriate intervention for hearing rehabilitation.1) As clinical experience and long term results of initial NHS programs are collected, special attention is directed to neonatal population with higher risk for hearing impairment. It is estimated that the prevalence of unilateral or bilateral hearing loss incidence of hearing impairment higher is as high as 3.2% in NICU population form a national cohort study.7) Also, established risk factors for hearing loss are more frequently encountered in NICU graduates than wellbaby nursery infants.8) Higher incidence of auditory neuropathy/auditory dyssynchrony (AN/AD) in NICU babies was also reported. The 2007 position statement of JCIH has outlined distinct protocols for hearing screening in wellbaby nurseries and NICU, and specified the usage of automated ABR in NICU infants. Traditional TEOAE tests have been utilized for a two-staged protocol for NHS program in all neonates admitted in wellbaby nursery and NICU in our hospital. As the demand for more comprehensive and definitive diagnostic evaluation is in demand for babies with various medical conditions in tertiary referral centers, a review of the current NHS program was attempted. It was encouraging to note that the results of the TEOAE screening protocol were in accordance with previous reports of referral rates.9,10,11,12) Also, the rate of follow up loss of 6.04% was comparable. Possible explanations for follow up loss during the NHS programs are considered similar to other institutes. Some neonates may be transferred to other hospitals before completion of hearing screening. Parents or even medical staff may prioritize management of other conditions more importantly than evaluation of hearing. Further efforts are needed to provide more information about the risk of hearing impairment and importance of early detection and intervention to parents and the medical staff. Also, the results or the lack of NHS should be noted in medical records for transfer to other hospitals. A significant finding concerns the false-negative case from the NHS protocol. Follow up audiological evaluation revealed normal TEOAE results, but delayed waves and increased threshold in ABR. The case correlates with AN/AD, where the usage of TEOAE as the sole hearing screening method is limited. Since the prevalence of AN/AD is considered higher in NICU infants, it may be speculated that there were other cases of false negative. Although a prospective cohort study of NICU graduates with longterm follow-up of audiological evaluations is prerequisite for accurate assessment of our two-staged TEOAE test protocol, even a general overview of the NHS program results supports the addition of ABR or A-ABR into the NHS program for NICU babies with higher risk for hearing impairment. Conclusion Timely and adequate screening of hearing loss is prerequisite for accurate diagnosis and appropriate rehabilitation in infants especially from NICU. Our data suggests that in selected population of NICU babies, NHS program utilizing TEOAE as two-stage testing method presents potential risk of failing to identify cases of neural hearing loss that may exert adverse effect on language development. Further refinement of the current NHS with additional ABR testing is required for more accurate and successful screening program. REFERENCES: 1.American Academy of Pediatrics, Joint Committee on Infant Hearing. Year 2007 position statement: principles and guidelines for early hearing detection and intervention programs. Pediatrics 2007;120:898-921. 2.Yoshinaga-Itano C, Gravel JS. The evidence for universal newborn hearing screening. Am J Audiol 2001;10:62-4. 3.Korres SG, Balatsouras DG, Gkoritsa E, Eliopoulos P, Rallis E, Ferekidis E. Success rate of newborn and follow-up screening of hearing using otoacoustic emissions. Int J Pediatr Otorhinolaryngol 2006;70:1039-43. 4.van Straaten HL, Hille ET, Kok JH, Verkerk PH; Dutch NICU Neonatal Hearing Screening Working Group. Implementation of a nation-wide automated auditory brainstem response hearing screening programme in neonatal intensive care units. Acta Paediatr 2003;92:332-8. 5.Joint Committee on Infant Hearing. 1994 position statement. ASHA 1994;36:38-41. 6.Joint Committee on Infant Hearing; American Academy of Audiology; American Academy of Pediatrics; American Speech-Language-Hearing Association; Directors of Speech and Hearing Programs in State Health and Welfare Agencies. Year 2000 position statement: principles and guidelines for early hearing detection and intervention programs. Joint Committee on Infant Hearing, American Academy of Audiology, American Academy of Pediatrics, American Speech-Language-Hearing Association, and Directors of Speech and Hearing Programs in State Health and Welfare Agencies. Pediatrics 2000;106:798-817. 7.Hille ET, van Straaten HI, Verkerk PH; Dutch NICU Neonatal Hearing Screening Working Group. Prevalence and independent risk factors for hearing loss in NICU infants. Acta Paediatr 2007;96:1155-8. 8.Vohr BR, Widen JE, Cone-Wesson B, Sininger YS, Gorga MP, Folsom RC, et al. Identification of neonatal hearing impairment: characteristics of infants in the neonatal intensive care unit and well-baby nursery. Ear Hear 2000;21:373-82. 9.Lim HW, Han MW, Lee HS, Kim KS, Chung JW, Kim YJ, et al. The validity using two-stage automated auditory brainstem response as a universal newborn hearing screening protocol: experiences in Asan medical center. Korean J Otolaryngol-Head Neck Surg 2007;50:108-14. 10.Park HJ, Park KH, Oh JH, Lee JS. TEOAE as a Newborn Hearing Screening. Korean J Otolaryngol-Head Neck Surg 1999;42:565-9. 11.Ohl C, Dornier L, Czajka C, Chobaut JC, Tavernier L. Newborn hearing screening on infants at risk. Int J Pediatr Otorhinolaryngol 2009;73:1691-5. 12.Suppiej A, Rizzardi E, Zanardo V, Franzoi M, Ermani M, Orzan E. Reliability of hearing screening in high-risk neonates: comparative study of otoacoustic emission, automated and conventional auditory brainstem response. Clin Neurophysiol 2007;118:869-76.