Improving newborn hearing screening: Are automated auditory brainstem response ear inserts an effective option?

Abstract

Objective

Universal newborn hearing screening is an established practice among Hong Kong public hospitals using a 2-stage automated auditory brainstem response (AABR) screening protocol. To enhance overall efficiency without sacrificing program accuracy, cost reduction in terms of replacing the initial ear coupler-based screening with a more economical ear insert-based screening procedure was considered. This study examined the utility of an insert-based AABR initial screening approach and the projected cost-effectiveness of a combined probe-based plus follow-up ear coupler AABR screening procedure.

Methods

Following prenatal maternal consent, newborn hearing screening was conducted with167 healthy neonates using a cross-sectional, repeated measures study design. The neonates were screened with AABR sequentially; using ear coupler and ear probe (insert) procedures, in both ears, with two different but comparable AABR instruments. Testing took place in the antenatal ward of a department of obstetrics and gynaecology, at a large public hospital.

Results

With the specific combination of instruments deployed for this study insert-based AABR screening generated a five-fold higher rescreen rate and took an additional 50% screening time compared to coupler-based AABR screening. Although the cost of consumables used in a 2-stage AABR screening protocol would reduce by 9.87% if the combined procedure was implemented, the findings indicated AABR screening when conducted with an ear probe has reduced utility compared with conventional ear coupler screening.

Conclusions

Significant differences may occur in screening outcomes when changes are made to coupler method. Initiating a 2-stage AABR screening protocol with an ear insert technique may be impracticable in newborn nurseries given the greater number of false positive cases generated by this approach in the present study and the increased time required to carry out an insert-based procedure.

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.