International Journal of Pediatric Otorhinolaryngology
Improving newborn hearing screening: Are automated auditory brainstem response ear inserts an effective option?
Introduction
Universal neonatal hearing screening (UNHS) is widely practiced globally as a strategy to prevent hearing impairment. By “universal”, all neonates are screened for hearing loss, as opposed to targeted screening in which only neonates with identifiable risk factors are screened. In Hong Kong, as in many localities, automated auditory brainstem response audiometry (AABR) is used for screening neonates born at public hospitals [1]. The protocol employed is a two-stage AABR screening procedure, with initial screening performed during an infant's first day of life, and with those who fail receiving a second-stage screening before hospital discharge, normally within the infant's second day of life (Fig. 1). Those infants who fail twice are referred for diagnostic audiological evaluation after hospital discharge.
The Hong Kong newborn hearing screening program performs well when evaluated against international benchmarks [2]. Among the Year 2012 public hospital birth cohort, 98.18% of total live births completed screening and 1.62% failed the two-stage screening and required further diagnostic testing. However, the cost associated with screening is relatively high. The hardware cost of screening, excluding staff costs, was HKD87.3 per infant screened [3]. The annual program cost is thus estimated to be over four million Hong Kong dollars. A substantial portion of the screening cost involves purchase of disposable coupler earphones for channelling stimulus sounds into the newborn ear. A number of AABR screening devices offer a reusable test stimulus probe coupled with a single-use ear insert—potentially a more economical alternative. Clearly, a less expensive alternative that does not compromise test accuracy would be welcomed, but to date no study has explored the relative cost-effectiveness of using an ear probe approach to conduct neonatal AABR screening.
Two broad concerns regarding probe-based AABR screening can be identified. The first is related to the stability of stimulus intensity. Compared to an ear probe, a coupler earphone allows more secure placement as its self-adhesive property prevents earphone shifts, and it requires less skilful technique for proper placement due to its over-the-ear design [4]. Additionally, elevation of stimulus level may occur when a probe is coupled to a small cavity, as in a newborn ear [5], and fluctuations in stimulus level can be caused by a loosely fitting stimulus probe. However, insert probe-compatible AABR screeners with in-the-ear stimulus calibration capability are now available. In-the-ear stimulus calibration adjusts speaker output level according to the ear canal volume detected, with the purpose of maintaining stimulus intensity to a desirable screening level, regardless of variations in ear cavity size.
A second major concern is that probe-based AABR neonatal screening can be adversely affected by the transient presence of vernix or debris in the external ear canal. Vernix is a waxy substance covering foetal skin and remains in the external ear canal of up to one-third of infants aged 48 h or less [6]. Its presence during otoacoustic emission newborn hearing screening can cause various degrees of probe obstruction, stimulus attenuation, and the attenuation of otoacoustic emissions recordable at the measurement probe, thereby increasing the likelihood of false positives [7]. However, AABR screening is less susceptible to these problems as auditory brainstem responses are recorded from scalp electrodes and not via a probe [8].
Since disposable ear inserts cost substantially less than a pair of disposable coupler earphones [3], converting from coupler screening to insert probe screening could enhance overall cost effectiveness of a 2-stage AABR UNHS protocol. The present study was designed to determine whether an alternative to a conventional AABR screening protocol could reduce hardware costs with little or no increase in other screening costs. The alternative AABR protocol involved use of a stimulus probe, with conventional ear coupler screening reserved only for newborns who failed initial probe screening. If probe screening generates no, or only a small number of additional, false positive findings then it may be effective to use a probe screening technique as a first-stage procedure. This would contribute to program cost reduction, with little increase in overall screening workload.
Section snippets
Ethical considerations
Ethical approval was obtained from the Research Ethics Committee (Kowloon Central/Kowloon East) of the Hong Kong Hospital Authority, and the Human Research Ethics Committee for Non-Clinical Faculties of the University of Hong Kong. All parents of participants gave their written informed consent to the study. The objectives of the study, procedures, withdrawal rights, and confidentiality issues were discussed orally and provided in written form.
Participants
Parental consent was obtained in the antenatal ward
Results
Attempts were made to screen both ears of all 167 study infants using the two stimulus input procedures. Among the 334 ears, all completed the coupler-based AABR screening, whereas 27 ears did not complete the probe-based AABR screening due to agitated infant state (n = 22 ears), high electrode impedance (n = 4 ears), or narrow canal opening (n = 1 ear).
Qualitative descriptions of infant activity level, degree of probe occlusion, degree of probe fit achieved, and overall noise levels during screening
Discussion
The current study set out to determine whether replacing coupler screening by ear probe screening in the initial stage of a 2-stage AABR UNHS protocol would enhance effectiveness in terms of reduced consumables cost with little increase in screening time. Results from the projected consumables cost analysis supported the alternative screening protocol. However, the additional 50% increase in screening time per bilaterally-passed infant, and five-fold higher required re-screen rate, which
Conclusions
Using a sequential testing procedure, this study revealed half of the newborn participants failed a probe-based AABR screening procedure, whereas only one in ten failed a coupler-based AABR screening. On average, probe screening time was 50% longer than coupler screening time among bilaterally passing neonates. The proposed alternative screening protocol that involved an initial probe-based and follow-up coupler-based AABR screening procedure could reduce by 10% the cost of consumables compared
Conflict of interest statement
None.
Acknowledgements
We thank Natus Medical Inc. who provided the Echo-Screen® III Pro device and all consumables used in the study, and to Ms. Crystal Cheung and her colleagues at Suburfarm Investment and Trading Co. Ltd., for helpful and timely technical assistance. We also wish to thank two anonymous reviewers for their valuable comments on a previous version of this report.
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