Establishing normative values for auditory brainstem response measurements among infants aged 3 to 6 months: descriptive study
SPMC J Health Care Serv. 2024;10(1):7 ARK: https://n2t.net/ark:/76951/jhcs4mh2z3
1Department of Otolaryngology–Head and Neck Surgery, Southern Philippines Medical Center, JP Laurel Ave, Davao City, Philippines
Correspondence Ed Levi L Camarillo, cedlevi@yahoo.com
Received 24 April 2023
Accepted 7 June 2024
Cite as Camarillo ELL, Laganao CRD. Establishing normative values for auditory brainstem response measurements among infants aged 3 to 6 months: descriptive study. SPMC J Health Care Serv. 2024;10(1):7. https://n2t.net/ark:/76951/jhcs4mh2z3
Introduction
The detection, diagnosis, and treatment of hearing impairments among the pediatric population have been an ongoing global concern.1 In the Philippines, the Republic Act (RA) 9709, also known as the Universal Newborn Hearing Screening and Intervention Act, was approved to address the impact of hearing impairment in children through early identification and accurate diagnosis of hearing loss.1
The auditory brainstem response (ABR) is an essential tool for assessing potential hearing loss in the pediatric population.3 4 This test is an objective method for assessing auditory function from the peripheral auditory system to the lower brainstem response to an auditory stimulus.4 At the Southern Philippines Medical Center (SPMC), the ABR test is relatively new and is only performed on patients with indications. Currently, the institution uses the adult normative values for the ABR test results of pediatric patients referred for the procedure. Since absolute and interpeak latencies of the waves would depend on factors such as age, stimulus parameters, and the equipment used, it is important to establish normative data for this population in each clinic.3 5 6 7 Typically, patients with normal hearing are tested to create a single set of normative values for future reference. These values are calculated based on the means, standard deviations and normal cutoff limits among these patients.6
We did this study to establish normative values for ABR measurements—absolute latencies for waves I, III, V, and interpeak latencies for waves I-III, III-V, and I-V—among infants aged 3 to 6 months based on ABR test results at SPMC's Department of Otorhinolaryngology - Head and Neck Surgery (ORL-HNS).
Methodology
Setting
We conducted a retrospective cross-sectional study among healthy infants with available ABR test results performed at the Audiology Unit of the Department of ORL-HNS of SPMC from January 2021 to December 2022. The audiology clinic started offering ABR testing in 2021, serving an average of 30 patients annually.
Participants
Infants up to 12 months old with normal otoacoustic emissions (OAE) test results from the Newborn Hearing Screening unit, and normal appearance of the external ears and eardrums as examined by a resident physician of the Department of ORL-HNS, were eligible for inclusion in the study. We excluded patients with consistent "refer" OAE results, illness during birth or upon the outpatient department encounter, and congenital deformity. Patients with ABR test results with abnormal values or with different stimulus and acquisition parameters based on records were also excluded.
In order to create a set of normative values for the ABR test, it is recommended to test 15-30 patients with normal hearing.6 In our study, we included all patients who had undergone ABR testing in the SPMC's Department of ORL-HNS since the department started using the current ABR equipment in 2021. Out of the 67 patients who had undergone the ABR test in our institution from January 2021 to December 2022, only 12 patients were eligible to be included in the study.
Data collection
We reviewed the medical records of each patient included in the study. From the records, we collected data on age and sex. We also collected data on the ABR test results of each patient, including the absolute latency readings for wave I, III, and V. We also recorded the results for the interpeak latencies for waves I-III, III-V, and I-V.
ABR testing was performed while the patients were in natural sleep. Surface electrodes—inverting electrodes on the right and left mastoids, a positive or non-inverting electrode on the vertex or the high forehead, and a ground electrode on the lower forehead—were attached to a computer and recorded the ABRs. Acoustic stimuli, in the form of rarefaction and condensation clicks at an intensity of 60-90 decibels normal Hearing Level (dBnHL), and at a rate of 45.1 clicks/sec, were delivered through insert earphones. The resulting waveforms were evaluated for morphology, reproducibility, and latency using OtoAccess® version 1.5 software and were observed by the examiner. The stimuli were presented at decreasing intensity levels in 10 dB steps until wave V is unidentifiable. All ABR tests were performed in a 1.45m x 2.68m room with an ambient noise of 30 dB and a temperature of 19-21℃. The instrument used for all tests was an Interacoustics Eclipse EP15 apparatus with a RadioEar IP30 Insert Earphone transducer.
Statistical analysis
In this study, categorical variables are reported as frequencies and percentages. Continuous variables are reported as means and standard deviations (SD). We used the Shapiro-Wilk test to check if the continuous variables were normally distributed. For variables that were not normally distributed, we checked for outliers and censored them in the analysis. To create a set of normative data values for both absolute latency waves and interpeak latency waves, we subtracted 2 SD from the mean to determine the lower limits and added 2 SD to the mean to determine the upper limits.3 7 8 All statistical tests were conducted using Stata/BE 17.0.
Results
Of the 67 patients who underwent the ABR test at our institution, only 12 were included in the study. Table 1 shows the demographic and hearing profiles of the infants included. The mean age of the patients included was 3.75 ± 1.06 months; 8/12 (66.67%) were male, and 4/12 (33.33%) were female. The mean hearing threshold was 16.25 ± 6.08 dBnHL, and their wave V mean absolute latencies were 6.65 ± 0.26 milliseconds (msec) and 6.58 ± 0.37 msec for the right and left ears, respectively. The mean interaural latency difference was 0.19 ± 0.18 msec. Most patients (7/12; 58.33%) had an amplitude ratio of 2:1, while the remainder (5/12; 41.67%) had a ratio of 1:1.
| Table 1 Demographic and hearing profiles of infants | |
| Characteristics |
Values
(n=12) |
|---|---|
| Mean age ± SD, months | 3.75 ± 1.06 |
| Sex, frequency (%) | |
| Male | 8 (66.67) |
| Female | 4 (33.33) |
| Mean hearing threshold ± SD, dBnHL | 16.25 ± 6.08 |
| Mean absolute latency (Wave V) ± SD, msec | |
| Right | 6.65 ± 0.26 |
| Left | 6.58 ± 0.37 |
| Mean interaural latency (Wave V) difference ± SD, msec | 0.19 ± 0.18 |
| Amplitude ratio, frequency (%) | |
| 1:1 | 5 (41.67) |
| 2:1 | 7 (58.33) |
The results of ABR test, both for the absolute latencies and interpeak latencies among patients included in this study, are shown in Table 2. The mean absolute latencies for wave I, wave III, and wave V were 1.49 ± 0.15 msec, 4.45 ± 0.32 msec, and 6.65 ± 0.26 msec, respectively. The mean interpeak latencies of wave I-III, wave III-V, and wave I-V were 2.80 ± 0.22 msec, 2.19 ± 0.21 msec, and 4.99 ± 0.29 msec, respectively. To establish the normal ABR range for both absolute latencies and interpeak latencies, a threshold of ± 2 SD from the mean was calculated for all latencies. For the absolute latencies for waves I, III, and V, the computed normative values were 1.19-1.78 msec, 3.81-5.10 msec, and 6.12-7.17 msec, respectively. For the interpeak latencies between waves I-III, III-V, and I-V, the computed normative values were 2.36-3.23 msec, 1.78-2.61 msec, 4.41-5.57 msec, respectively.
| Table 2 Auditory brainstem response (ABR) wave measurements of infants. | |||
| Characteristics |
Values (n=12) |
Normative values* | |
|---|---|---|---|
| Absolute latency, msec | |||
| Wave I (n=10)† | 1.49 ± 0.15 | 1.19 to 1.78 | |
| Wave III | 4.45 ± 0.32 | 3.81 to 5.10 | |
| Wave V | 6.65 ± 0.26 | 6.12 to 7.17 | |
| Interpeak latency, msec | |||
| Wave I-III | 2.80 ± 0.22 | 2.36 to 3.23 | |
| Wave III-V | 2.19 ± 0.21 | 1.78 to 2.61 | |
| Wave I-V | 4.99 ± 0.29 | 4.41 to 5.57 | |
|
*threshold of ± 2 standard deviations from the mean †two outliers were censored |
|||
Discussion
Key results
In this study involving infants aged 3-6 months who had undergone ABR tests, we established normative value ranges for the Interacoustics Eclipse EP15 apparatus with a RadioEar IP30 Insert Earphone transducer. The ranges for absolute and interpeak latency waves were computed by subtracting and adding 2 SD from the mean values to determine the lower and upper limits.
Strengths and limitations
This study has provided a set of ABR normative values applicable for better audiologic diagnosis at the Department of ORL-HNS clinic of SPMC. However, there are limitations in this study: the normative values may only apply to infants aged 3 to 6 months due to the age range of our sample. Additionally, we lacked data on preterm birth status, which could significantly influence interpeak latency values.9 Our study also utilized a stimulus intensity range of 60-90 dBnHL and a stimulus rate of 45.1 clicks/sec, which may differ from other studies and affect normative values. Despite our efforts, the sample size in our study remains limited,6 impacting the rigor of our findings.
Interpretation
Various factors, including participant characteristics, stimulus variations, and differences in recording techniques, can significantly influence and distort ABR waveforms.10 Different devices and examiners may yield different results.11 Because these factors have the potential to alter the ABR outcomes, relying solely on generalized ABR norms from textbooks could lead to inaccurate evaluations. Therefore, it is recommended that each audiology facility develop standardized norms tailored to their specific testing equipment and patient demographics.
Among the measurements used in ABR analysis, our study focused on absolute and interpeak latencies. Absolute latencies of waves are generally consistent, with a variance of 0.1 msec in normal individuals, making them a highly accurate parameter for clinical interpretation of normal versus abnormal test results.7 12 These parameters are widely utilized by researchers investigating ABR.
The absolute and interpeak latencies, as well as the hearing threshold data from our study, were similar to findings from published studies.13 14 15 16 Interaural wave V differences ≤ 0.4 msec were observed across all subjects, consistent with findings in individuals with symmetrical hearing.15 17 Exceeding upper values of normal ranges in absolute and interpeak latencies suggests abnormality, potentially indicating retrocochlear hearing loss.18 These pathologies can impair the proper functioning of anatomical structures such as the proximal and distal portions of the auditory nerve, cochlear nucleus, superior olivary complex, lateral lemniscus, and inferior colliculus, allowing for diagnosis through these values.19
Generalizability
The results of the study are applicable to infants who may have potential hearing loss. However, it is important to note that infants born preterm may exhibit higher interpeak latencies due to abnormal brainstem maturation. Consequently, infants with lower gestational age have greater delays in auditory conduction.9 Additionally, some ABR audiology equipment may feature more or less advanced capabilities or stimuli compared to the apparatus used in our study, potentially resulting in longer latencies with lower stimulus intensities and faster repetition rates.20
Conclusion
In this descriptive study of infants undergoing ABR tests, we have established normative values for absolute and interpeak latency waves using the Interacoustics Eclipse EP15 apparatus with a RadioEar IP30 Insert Earphone transducer, employing a stimulus intensity of 60-90 dBnHL and a rate of 45.1 clicks/sec.
Contributors
ELLC and CRDL had substantial contributions to the study design, and to the acquisition, analysis and interpretation of data. ELLC wrote the original draft and subsequent revisions. All authors reviewed, edited, and approved the final version of the manuscript. All authors agreed to be accountable for all aspects of the work.
Ethics approval
This study was reviewed and approved by the Davao Center for Health Development Joint Research Ethics Committee (JREC-2022147).
Reporting guideline used
Article source
Submitted
Peer review
External
Funding
Supported by personal funds of the authors
Competing interests
None declared
Access and license
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Copyright © 2024 ELL Camarillo, et al.
Published
June 25, 2024
Issue
Volume 10 Issue 1 (2024)
Section
Research
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