Influence of acquisition parameters on the measurement of click evoked otoacoustic emissions in neonates in a hospital environment

Changes in transient-evoked otoacoustic emissions in the first month of life

OBJECTIVE

Current Joint Committee on Infant Hearing guidelines recommend the use of transient-evoked otoacoustic emissions (TEOAEs) as a screening tool to identify hearing loss for newborns cared for in the well-baby nursery. Newborns who do not pass the TEOAE screen before leaving the hospital are typically rescreened as outpatients by 1 mo of age, at which time, approximately 50 to 70% pass screening criteria. To better understand why many infants are referred at initial screening but pass at the rescreening, more complete knowledge of developmental differences in the TEOAE levels, noise floor, or a combination of both for infants who pass and fail birth screening is needed. In addition, it has been shown that infants with occluding ear-canal debris are more likely to not pass TEOAE screening at the hospital than those without occluding ear-canal debris. This study explores whether changes in TEOAE levels in half-octave frequency bands are related to changes in ear-canal debris over the first month of life.

DESIGN

Seventy-nine neonates from a well-baby nursery had their hearing screened before leaving the hospital and again at approximately 1 mo of age. All participants passed the follow-up screening. Overall TEOAE levels and levels in half-octave frequency bands centered at 1.5, 2, 3, and 4 kHz were measured. Judgments of ear-canal debris were made by otoscopy and were rated using one of three categories at both visits.

RESULTS

TEOAE levels in infants significantly increased from birth to 1 mo of age across all frequencies tested, regardless of whether they passed or failed the screening at birth. The increase in TEOAE level was frequency dependent, with the greatest increases occurring in the highest frequency bands. No significant correlation between debris change and frequency-specific changes was found for either ear. Infants who failed the screening at birth but who subsequently passed at 1 mo of age had significantly lower TEOAE levels at the rescreening than did infants with passing TEOAE levels at birth. However, pass/fail status at birth was only a weak predictor of TEOAE levels at 1 mo of age.

CONCLUSIONS

The increase in TEOAE levels during the first month of life is frequency dependent, with greater increases occurring at higher frequencies. Increased TEOAE levels were not associated with changes in ear-canal debris.

Using benefit-cost ratio to select Universal Newborn Hearing Screening test criteria

OBJECTIVES

Current protocols presumably use criteria that are chosen on the basis of the sensitivity and specificity rates they produce. Such an approach emphasizes test performance but does not include societal implications of the benefit of early identification. The purpose of the present analysis was to evaluate an approach to selecting criteria for use in Universal Newborn Hearing Screening (UNHS) programs that uses benefit-cost ratio (BCR) to demonstrate an alternative method to audiologists, administrators, and others involved in UNHS protocol decisions.

DESIGN

Existing data from more than 1200 ears were used to analyze BCR as a function of Distortion Product Otoacoustic Emission (DPOAE) level. These data were selected because both audiometric and DPOAE data were available on every ear. Although these data were not obtained in newborns, this compromise was necessary because audiometric outcomes (especially in infants with congenital hearing loss) in neonates are either lacking or limited in number. As such, it is important to note that the characteristics of responses from the group of subjects that formed the bases of the present analyses are different from those for neonates. This limits the extent to which actual criterion levels can be selected but should not affect the general approach of using BCR as a framework for considering UNHS criteria. Estimates of the prevalence of congenital hearing loss identified through UNHS in 37 states and U.S. territories in 2004 were used to calculate BCR. A range of estimates for the lifetime monetary benefits and yearly costs for UNHS were used, based on data available in the literature. Still, exact benefits and costs are difficult to know. Both one-step (DPOAE alone) and two-step (DPOAE followed by automated auditory brainstem response, AABR) screening paradigms were considered in the calculation of BCR. The influence of middle ear effusion was simulated by incorporating a range of expected DPOAE level reductions into an additional BCR analyses

RESULTS

Our calculations indicate that for a range of proposed benefit and cost estimates, the monetary benefits of both one-step (DPOAE alone) and two-step (DPOAE followed by AABR) NHS programs outweigh programmatic costs. Our calculations indicate that BCR is robust in that it can be applied regardless of the values that are assigned to benefit and cost. Maximum BCR was identified and remained stable regardless of these values; however, it was recognized that the use of maximum BCR could result in reduced test sensitivity and may not be optimal for use in UNHS programs. The inclusion of secondary AABR screening increases BCR but does not alter the DPOAE criterion level at which maximum BCR occurs. The model of middle ear effusion reduces overall DPOAE level, subsequently lowering the DPOAE criterion level at which maximum BCR was obtained

CONCLUSION

BCR is one of several alternative methods for choosing UNHS criteria, in which the evaluation of costs and benefits allows clinical and societal considerations to be incorporated into the pass/refer decision in a meaningful way. Although some of the benefits of early identification of hearing impairment cannot be estimated through a monetary analysis, such as improved psychosocial development and quality of life, this article provides an alternative to audiologists and administrators for selecting UNHS protocols that includes consideration of societal implications of UNHS screening criteria. BCR suggests that UNHS is a worthwhile investment for society as benefits always outweigh costs, at least for the estimations included in this article. Although the use of screening criteria that maximize BCR results in lower test sensitivity compared with other criteria, BCR may be used to select criteria that result in increased test sensitivity and still provide a high, although not maximal, BCR. Using BCR analysis provides a framework in which the societal implications of NHS protocols are considered and emphasizes the value of UNHS.

Tone burst-evoked otoacoustic emissions in neonates: normative data

BACKGROUND

Tone-burst otoacoustic emissions (TBOAEs) have not been routinely studied in pediatric populations, although tone burst stimuli have greater frequency specificity compared with click sound stimuli. The present study aimed (1) to determine an appropriate stimulus level for neonatal TBOAE measurements when the stimulus center frequency was 1 kHz, (2) to explore the characteristics of 1 kHz TBOAEs in a neonatal population.

METHODS

A total of 395 normal neonates (745 ears) were recruited. The study consisted of two parts, reflecting the two study aims. Part I included 40 normal neonatal ears, and TBOAE measurement was performed at five stimulus levels in the range 60-80 dB peSPL, with 5 dB incremental steps. Part II investigated the characteristics of the 1 kHz TBOAE response in a large group of 705 neonatal ears, and provided clinical reference criteria based on these characteristics.

RESULTS

The study provided a series of reference parameters for 1 kHz TBOAE measurement in neonates. Based on the results, a suggested stimulus level and reference criteria for 1 kHz TBOAE measures with neonates were established. In addition, time-frequency analysis of the data gave new insight into the energy distribution of the neonatal TBOAE response.

CONCLUSION

TBOAE measures may be a useful method for investigating cochlear function at specific frequency ranges in neonates. However, further studies of both TBOAE time-frequency analysis and measurements in newborns are needed.

Neonatal hearing screening: a combined click evoked and tone burst otoacoustic emission approach

OBJECTIVE

This study evaluated an alternative transient evoked otoacoustic emissions method for screening hearing in newborn babies that may reduce the referral rate of initial screening.

METHODS

A total of 1,033 neonates (2,066 ears) from two hospitals were recruited. Subjects had their hearing screened in both ears using a combined approach-both click evoked OAEs (CEOAEs) and 1kHz tone burst evoked OAEs (TBOAEs).

RESULTS

1kHz TBOAEs were more robust than CEOAEs in terms of emission response level and signal-to-noise ratio (SNR) at both 1 and 1.5kHz frequency bands. The prevalence rate for CEOAE and TBOAE responses in these two frequency bands was significantly different. The combined protocol significantly reduced the referral rate-by almost 2 percentage points for first time screening.

CONCLUSIONS

The implementation of a combined 1kHz TBOAE/CEOAE screening protocol is a feasible and effective way to reduce referral rates, and hence false positive rates, in neonatal hearing screening programs.

Click-evoked otoacoustic emissions (CEOAEs) recorded from neonates under 13 hours old using conventional and maximum length sequence (MLS) stimulation

Maximum length sequence (MLS) stimulation allows click evoked otoacoustic emissions (CEOAEs) to be averaged at very high stimulation rates. This enables a faster reduction of noise contamination of the response, and has been shown to improve the signal-to-noise ratio (SNR) of CEOAEs recorded from adult subjects. This study set out to investigate whether MLS averaging can enhance the SNR of CEOAEs recorded in newborns within the first day after birth, and so improve the pass rates for OAE screening in this period, when false alarm rates are very high. CEOAEs were recorded in a neonatal ward from 57 ears in 37 newborns ranging from 6 to 13h old, using both conventional (50/s) and high rate (5000/s) MLS averaging. SNR values and pass rates were compared for responses obtained within equal recording times at both rates. MLS averaging produced an SNR improvement of up to 3.8dB, with the greatest improvement found in higher frequency bands. This SNR advantage resulted in pass rate improvement between 5% and 10%, depending on pass criterion. A significant effect of age was found on both SNR and pass rate, with newborns between 6 and 10h old showing significantly lower values than those tested between 10 and 13h after birth, as well as a much greater improvement due to MLS averaging. The findings show that MLS averaging can reduce false alarm rates by up to 15% in very young neonates in a neonatal ward setting.

Neonatal hearing screening: evaluation of tone-burst and click-evoked otoacoustic emission test criteria

OBJECTIVE

Click-evoked otoacoustic emissions (CEOAEs) are widely used in universal neonatal hearing screening programs. A common finding in many such programs is a relatively high false-positive rate. This is often due to infant physiological noise adversely affecting the emission recording, leading to a "refer" screening outcome. In an attempt to reduce false-positive screening outcomes related to the effects of noise on otoacoustic emission response detection, tone-burst-evoked otoacoustic emissions (TBOAEs) were included in a neonatal hearing screening program because TBOAEs may elicit a greater signal-to-noise ratio than CEOAEs. The research project compared the pass/refer rate for a CEOAE-based test using established pass/refer criteria with the pass/refer rate for screening criteria that were based on TBOAE results alone or on combined CEOAE and TEOAE results.

DESIGN

Neonates were recruited at the Hong Kong Adventist Hospital, and both CEOAEs and TBOAEs were performed. Six passing criteria were used in this study, based on CEOAEs only; CEOAEs plus 1 kHz TBOAEs; CEOAEs plus 2 kHz TBOAEs; CEOAEs plus 3 kHz TBOAEs; CEOAEs plus 1, 2, and 3 kHz TBOAEs; and TBOAEs only.

RESULTS

Data from 298 neonates (546 ears) were obtained. Criteria set 1, using CEOAEs only, demonstrated a pass rate of 79.1%, and 114 ears were referred. Criteria set 2, using CEOAEs together with TBOAEs recorded at 1 kHz, passed 39 more ears than Protocol 1, and the pass rate was 86.3%. Hence, the overall referral rate for total number of screened ears decreased by 7.2 percentage points. Criteria set 3, using CEOAEs together with TBOAEs recorded at 2 kHz, and Criteria set 4, using CEOAEs in conjunction with TBOAEs recorded at 3 kHz, gave pass rates similar to Criteria set 1. Criteria set 5, using TBOAE information at frequencies where CEOAEs were not rated as "pass," raised the pass rate from 79.1 to 87.6%, reducing the overall referral rate by 8.5 percentage points. Criteria set 6, in which neonates were screened with TBOAEs recorded at 1, 2, and 3 kHz, gave a pass rate of 78.4%, similar to results for the CEOAE-only procedure.

CONCLUSIONS

Both Criteria sets 2 and 5, which combined CEOAE and TBOAE recordings, gave significantly higher pass rates than Criteria sets 1, 3, 4, and 6. The results suggest that the introduction of combined CEOAE and TBOAE protocols may assist in the reduction of refer outcomes, and hence the false-positive rates, of neonatal hearing screening programs.

The hearing system in newborns from the Upper Silesia. Assessment of TEOAE depending on selected parameters of delivery disorders

Transient evoked otoacoustic emission (TEOAE) is an accepted test for screening of the cochlea function in newborns. In this study 300 newborns was tested using TEOAE, as well as analysing such parameters as birth weight, Apgar scale, bilirubinaemia. The study indicated the tendency of TEOAE to decrease in newborns with low birth weight and low Apgar scores. Hyperbilirubinaemia seems to have an influence on cochlea function monitored by TEOAE, especially if there were simultaneously low Apgar scores. A similar tendency, although slightly stronger, was observed in the preterm newborn group. TEOAE seems to be a good method of recording the negative influence on the cochlea activity such factors as low birth weight and asphyxia. Hyperbilirubinaemia with asphyxia acts upon the cochlea similarly. All these tendencies were observed more strongly in the preterm newborn group. It is concluded that TEOAE analysis demonstrated its utility as a screening test assessing the hearing state in newborns, additionally the associations of cochlea activity was found with a few parameters of delivery disorders.

A TEOAE screening protocol based on linear click stimuli: performance and scoring criteria

In order to improve the quality of current TEOAE recording methodologies, we have conducted a comparison of TEOAE neonatal recordings acquired with linear protocols using click stimuli of 68 dB SPL and non-linear protocols using the ILO default stimulus values. From a theoretical standpoint it was expected that the linear recordings would generate responses characterized by higher S/N ratios due to the fact that the stimulus sequence contains four clicks of the same intensity and polarity. The project included recordings from 1,416 neonatal ears (age 48 h). The TEOAE data were compared in terms of correlation, response amplitude, noise, corrected response and S/N ratio in the 1.0-, 2.0-, 3.0-, 4.0- and 5.0-kHz bands, using a paired t-test criterion. We found that windowed (4-14 ms) responses evoked by a linear TEOAE protocol generated superior S/N estimates in the 2.0-, 3.0-, 4.0- and 5.0-kHz TEOAE bands, in addition to superior correlation estimates, and demonstrated lower levels of noise. Clear-cut scoring criteria were established for the S/N ratios at 2.0, 3.0 and 4.0 kHz, by constructing one-sided distribution-free tolerance boundaries.