Abstract:
Hearing loss in early childhood and infancy often goes undetected because it exhibits no obvious indication and symptoms. The primary aim of newborn hearing screening is to detect permanent hearing loss. Since otoacoustic emissions (OAE) and automated auditory brainstem response (AABR) are sensitive to hearing loss, they are often used as screening tools. On the other hand, these screening tests can be affected by transient outer ear and middle ear conditions that are often present at birth. This is an especially characteristic state of affairs for NICU neonates. These false positive results may render screening programmes inefficient and can lead to increased parental anxiety. Wideband acoustic immittance (WAI) has shown potential for accurate assessment of middle ear function in neonates, and is therefore recommended as an adjunct tool for newborn hearing screening programmes. The main aim of the study was to determine the feasibility of using WAI in NICU neonates in terms of tone and click stimuli.
Testing was conducted in the NICU units of three private hospitals in Pretoria. As part of the selection criteria all the neonates had to pass both DPOAE and AABR screenings before they were included in the study. In total, 56 NICU infants (106 ears) with a gestation age of between 32 and 37 weeks and a mean gestational age of 35.6 weeks who passed both DPOAE and AABR hearing screens in one or both ears were selected. For WAI measurements there were two measurements, one for each channel in the probe (chirp and tone stimuli). Normative regions were defined across the wideband reflective spectrum for both tone and chirp stimuli and for integrated frequency ranges. The chirps and tone stimuli compared relatively well with each other at the 90th percentile with the same amount of reflectance across all frequencies. The median reflectance reached a minimum of 0.67 at 1-2 kHz but increased to 0.7 below 1 kHz and 0.72 above 2 kHz for the tone stimuli. For chirp stimuli the median reflectance reached a minimum of 0.51 at 1-2 kHz but increased to 0.68 below 1 kHz and decreased to 0.5 above 2 kHz.
Results of this study identified WAI patterns that had not previously been reported in the literature. High reflective values were obtained across all frequency ranges, especially in the frequency ranges below 3 kHz and above 4 kHz. The age of the neonates when tested (mean gestational age 35.6 weeks, with a standard deviation of 1.6) might have influenced the results. The neonates in this study were of a very young age compared to the ages of the infants in previous studies on WAI. Environmental noise in NICU might have influenced the results. Additional research is required to investigate WAI testing in ears with and without dysfunction.
