Hearing loss in graduates of a tertiary intensive care nursery

A study to evaluate the burden of hearing loss and its correlation with risk factors among high-risk infants at a teaching institution, Jaipur

Introduction

Hearing loss is a global issue of hearing disability and early detection and rehabilitation of hearing loss are important for the development of speech and language skills in hearing-impaired infants. There are multiple risk factors that aid in hearing loss but some are potential factors that contribute toward hearing loss in infants. The aim of this study was to assess the burden of hearing loss and its correlation with risk factors among high-risk infants at a teaching institution in Jaipur, Rajasthan.

Method

This study was carried out after approval of institutional ethics committee on a total of 320 high-risk infants at RUHS College of medical sciences and associated hospitals. Hearing loss was assessed by brainstem evoked response audiometry (BERA). Statistical analysis of data was done by cross-tabulation analysis with Pearson correlation and quantile regression.

Results

Out of 320 high-risk infants, 59.69% of infants had normal hearing, 9.09% Unilaterally hearing impaired, 20.31% were bilaterally mild-moderate hearing loss, and 10.94% had severe-profound deafness. The prevalence of important risk factors viz. hyperbilirubinemia, low birth weight, appearance, pulse, grimace, activity, and respiration score, meconium aspiration, respiratory distress, and ventilation greater than five days were 86%, 58.9%, 40%, 36%, 29%, and 22%, respectively.

Conclusion

In high-risk infants, hearing loss is a common hearing disorder. Because of this, early diagnosis of hearing loss gives them the best chance of developing functional speech. Brainstem evoked response audiometry is a simple, reliable, and effective technique for the assessment of auditory functions in infants.

Efficacy of auditory evoked potential follow-up in viral meningitis of infants

PURPOSE

To examine the rate of occurrence of hearing impairments among the infants who had recovered from viral meningitis under 1 year of age through auditory evoked potential (AEP) test and to investigate the efficacy of the follow-up AEP test in viral meningitis infants.

METHODS

Two hundred twenty infants (440 ears) were examined through AEP test once, and 47 (94 ears) of them went back for a second examination and were diagnosed with viral meningitis. The first AEP tests were compared with the second results in 47 infants. I latency, V latency, I-III interpeak latency (IPL), and III-V IPL were checked.

RESULTS

In the first AEP test conducted on 440 ears, the average values of I and V latency and I-III IPL were delayed as compared with normal values. The second AEP results were conducted on 47 infants 92.36 days after the first exam. I latency and V latency of second exam were improved significantly (p < 0.05), but I-III and III-V IPL showed no significant changes. Two hearing impaired patients (4 ears) were confirmed through chart reviews.

CONCLUSION

The AEP test is a helpful study for early detection of hearing problem. However, in this study, AEP test was too sensitive in acute period, and later, the incidence rate of hearing impairment was relatively low. Therefore, age of onset, severity of neurologic symptom, and clinical examination must be considered before the AEP test.

Neurodevelopment and asymmetry of auditory-related responses to repetitive syllabic stimuli in preterm neonates based on frequency-domain analysis

Sensory development of the human brain begins prenatally, allowing cortical auditory responses to be recorded at an early age in preterm infants. Despite several studies focusing on the temporal characteristics of preterm infants' cortical responses, few have been conducted on frequency analysis of these responses. In this study, we performed frequency and coherence analysis of preterm infants' auditory responses to series of syllables and also investigated the functional brain asymmetry of preterm infants for the detection of the regularity of auditory stimuli. Cortical auditory evoked potentials (CAEPs) were recorded in 16 preterm infants with a mean recording age of 31.48 weeks gestational age (29.57-34.14 wGA) in response to a repetitive syllabic stimulus. Peak amplitudes of the frequency response at the target frequency and the first harmonic, as well as the phase coherence (PC) at the target frequency were extracted as age-dependent variables. A functional asymmetry coefficient was defined as a lateralization index for the amplitude of the target frequency at each electrode site. While the findings revealed a significant positive correlation between the mean amplitude at the target frequency vs. age (R2 = 0.263, p = 0.042), no significant correlation was observed for age-related changes of the mean amplitude at the first harmonic. A significant correlation was also observed between the mean PC and age (R2 = 0.318, p = 0.023). A right hemisphere lateralization over many channels was also generally observed. The results demonstrate that rightward lateralization for slow rate modulation, previously observed in adults, children and newborns, appears to be in place at a very young age, even in preterm infants.

Neurodevelopmental Hypothesis about the Etiology of Autism Spectrum Disorders

Previous models or hypotheses of autism spectral disorder (ASD) failed to take into full consideration the chronological and causal developmental trajectory, leading to the emergence of diverse phenotypes through a complex interaction between individual etiologies and environmental factors. Those phenotypes include persistent deficits in social communication and social interaction (criteria A in DSM-5), and restricted, repetitive patterns of behavior, interests, or activities (criteria B in DSM-5). In this article, we proposed a domain-general model that can explain criteria in DSM-5 based on the assumption that the same etiological mechanism would trigger the various phenotypes observed in different individuals with ASD. In the model, we assumed the following joint causes as the etiology of autism: (1) Hypoplasia of the pons in the brainstem, occurring immediately following neural tube closure; and (2) Deficiency in the GABA (γ-aminobutyric acid) developmental switch during the perinatal period. Microstructural abnormalities of the pons directly affect both the structural and functional development of the brain areas strongly connected to it, especially amygdala. The impairment of GABA switch could not only lead to the deterioration of inhibitory processing in the neural network, but could also cause abnormal cytoarchitecture. We introduced a perspective that atypical development in both brain structure and function can give full explanation of diverse phenotypes and pathogenetic mechanism of ASD. Finally, we discussed about neural mechanisms underlying the phenotypic characteristics of ASD that are not described in DSM-5 but should be considered as important foundation: sleep, global precedence, categorical perception, intelligence, interoception and motor control.

A neurobiological model for the effects of early brainstem functioning on the development of behavior and emotion regulation in infants: implications for prenatal and perinatal risk

Neurobiological models propose an evolutionary, vertical-integrative perspective on emotion and behavior regulation, which postulates that regulatory functions are processed along three core brain systems: the brainstem, limbic, and cortical systems. To date, few developmental studies applied these models to research on prenatal and perinatal risk. We propose a conceptual model that incorporates three integrated levels of observations for the study of early risk: (a) brainstem-related physiological regulation of cyclic processes and sensory integration, e.g., vagal regulation, circadian rhythms; (b) emotion and attention regulation capacities that draw on the integration of brainstem and limbic systems; and (c) higher-level outcomes that draw on the intactness of brainstem and limbic networks, including socio-emotional self-regulation, inhibitory control, and cognitive processing. We discuss implications of the model for the development of regulatory capacities during the prenatal and early postnatal stages in infants born with specific perinatal risk. We underscore the importance of assessing sub-cortical and brainstem systems and the longitudinal effects of transitory brainstem dysfunction on physiological homeostasis, motivation, arousal-modulated attention, stress reactivity, and mother-infant co-regulation. The assessment of brainstem dysfunction can be conducted during hospitalization and may help detect infants at risk for the development of self-regulatory deficits at the first weeks of life.

Initial Audiologic Assessment of Infants Referred From Well Baby, Special Care, and Neonatal Intensive Care Unit Nurseries

Purpose

The purpose of the study was to evaluate the effectiveness of a 2-hr initial audiologic assessment appointment for infants referred from area universal newborn hearing screening (UNHS) programs to a clinical audiology department in an urban hospital.

Method

A prospective auditory brainstem response (ABR)-based protocol, including clicks, frequency-specific tone bursts, and bone-conducted stimuli, was administered by 10 audiologists to 375 infants. Depending on the ABR findings, additional test options included distortion product otoacoustic emissions (DPOAEs), high-frequency tympanometry, and/or otologic examination.

Results

In 88% of the 2-hr test sessions, at least 4 ABR threshold estimates were obtained (i.e., bilateral clicks and either a 500- or 1000-Hz tone burst and a 4000-Hz frequency tone burst for the better ear). The incidence of hearing loss was significantly different across nursery levels: 18% for Level I (well baby), 29% for Level II (special care), and 52% for Level III (neonatal intensive care unit). Hearing loss type was defined at the initial assessment for 35 of the 51 infants with bilateral hearing loss based on bone-conduction ABR, latency measures, DPOAEs, high-frequency tympanometry, and/or otologic examination.

Conclusions

Our findings indicate that a 2-hr test appointment is appropriate for all nursery levels to diagnose severity and type of hearing loss in the majority of infants referred from UNHS. Examination by an otolaryngologist within 24–48 hr further defines the hearing loss and facilitates treatment plans.

Evaluation of hearing loss in infants and young children

The identification, assessment, and management of hearing impairment in the pediatric population can be a challenging endeavor. Nevertheless, newer technology, improved techniques, and the cooperative efforts of various professional organizations and their constituencies have made significant strides toward achieving this goal. As more precise objective technologies are introduced, there will be a tendency to rely more heavily on their application. Both IA and OAEs have already made significant impact in pediatric practices because of their ease and simplicity. Within a short period of time, trained technical staff can become proficient in their usage and test interpretation. Their application in conjunction with basic audiometry can provide a global picture of auditory status (Table 2). However, it is critical to recall that the basic building block of auditory assessment is the audiogram, a true measure of behavioral threshold sensitivity. Therefore, when test results suggest hearing impairment, appropriate audiological referral to the will ensure continuity of services and provision of rehabilitative measures. It is equally essential for primary care providers to understand the therapeutic needs of their patients and to manage and coordinate the medical aspects of the infant or child when hearing loss is suspected.

[Hypoacusis-deafness related to perinatal adverse conditions. According to the register available in a specialized unit of Ciudad de Mexico. Analysis according to birth weight]

OBJECTIVE

To analyse perinatal adverse conditions related with birth weight in 160 children with hearing impairment-deafness (prelingual sensorineural hearing loss) according to medical data of a specialized medical unit in Mexico City.

RESULTS

The average age of children was 4 years old +/- 1.7; 61% were male. 47.5% of the cases had a birthweight between 1,500 and 2,900 g. 90 cases (56%) had an abnormal delivery and 68 (42.5%) were first pregnancy cases. A high number of cases had delayed breathing, cyanosis, jaundice or respiratory failure. 104 cases (65%) had deafness and 56 (35%) presented. hearing loss. Only 11% of the children had a birth-weight under 1,500 g. 58% of all cases had a birth weight lower than 3,000 g.

CONCLUSION

The quality of medical assistance provided during the perinatal period has a very important role in origin of hearing impairment--deafness in this group of children. It is important to increase our knowledge about the perinatal adverse conditions in order to establish preventive programs.

Automated auditory brainstem response testing for universal newborn hearing screening

The goal of universal newborn hearing screening is to identify infants with hearing loss by 3 months of age and to provide appropriate intervention by 6 months of age. Automated auditory brainstem response helps accomplish this goal by providing a test that is easy to use, fast, cost-effective, and accurate. Universal newborn hearing screening with automated auditory brainstem response ensures that children with hearing loss are given the opportunity for early intervention and an improved quality of life.

A cost-effectiveness analysis of the high risk register and auditory brainstem response

OBJECTIVE

To evaluate an infant hearing screening program utilizing the high risk register (HRR) and auditory brainstem response (ABR).

DESIGN

A cost-effectiveness analysis of the screening program employing a retrospective cohort identified by chart review. The analysis was performed on a hypothetical cohort of 100,000 births and the results compared with a base model derived from literature review.

SETTING

Mount Sinai Hospital, New York City, an urban, tertiary care institution.

PATIENTS

All infants born between November 1990 and October 1993, approximately 16,500. Cost-effectiveness analysis focused on test results of 420 infants failing the HRR and 381 who subsequently received ABR.

RESULTS

Analysis of the Mount Sinai Hospital (MSH) protocol showed it to be less cost-effective than other similar programs. The cost per hearing loss was far more at MSH than that found elsewhere. Further, the MSH program was ineffective in detecting infants with congenital hearing loss--identifying only one case between 1990 and 1993. Analysis of high risk criteria finds a low incidence of family history of hearing loss in the Mount Sinai cohort while other studies find a very high incidence.

CONCLUSIONS

It appears that the poor performance of the MSH protocol is due to low specificity and sensitivity of the HRR. This generates a costly and ineffective program as follow-up exams focus on ruling-out false-positives rather than correctly identifying true hearing losses. Further evaluation is needed to determine whether changes in the application of the HRR or utilization of newer, low-cost tests such as otoacoustic emissions (OAE) may be effective in universal infant hearing screening.

Auditory brainstem response screening for hearing loss in high risk neonates

The present paper reports the findings of a 7 year study evaluating the use of the auditory brainstem response (ABR) as the basis of a hearing screening procedure in a group of newborns at increased risk of hearing impairment. A Special Care Baby Unit (SCBU) population of 417 infants with diverse clinical backgrounds and treatment histories was tested for hearing impairment at birth using ABR audiometry. Some 332 passed the original screen at 30 dBnHL test level in both ears. Of the failure group, 18 did not survive and 32 had some degree of hearing impairment confirmed, nine of which were sensorineural in origin. An increased incidence of persistent middle ear disease was also noted in the failure group. A detailed operational analysis demonstrates that provided appropriate pass/fail criteria are adopted, the ABR technique offers excellent sensitivity and specificity for the detection of significant hearing loss in the test population. Furthermore, the study establishes that implementation of an ABR-based screening programme could reduce the average age at detection of permanent hearing loss by 7 months. A cost assessment shows that the introduction of such a targetted screening procedure could be done at a reasonable outlay.

Type of initial brainstem auditory evoked potentials (BAEP) impairment and risk factors in premature infants

Brainstem auditory evoked potentials (BAEPs) were recorded in 89 premature infants aged between 34 and 52 weeks. 47.2% had normal and 52.8% abnormal BAEPs in at least one ear. Seven risk factors were taken into account: birth weight lower than 1500 g, hypoxia, neurological damage, fetal pathology, associated malformation, the use of ototoxic drugs, and exchange transfusion. The type of BAEP impairment was defined as either endocochlear, transmission or retrocochlear damage. Percentage BAEP impairment was higher in case of hypoxia (63.3%) but remained similar whether the other risk factors were present or absent. Transmission impairment was more frequent in case of birth weight lower than 1500 g, hypoxia or ototoxic drug administration; Endocochlear damage occurred more frequently when ototoxic drugs had been used or exchange transfusion performed. When birth weight was lower than 1500 g, transmission damage was more frequent than when birth weight was higher than 1500 g. In contrast, endocochlear damage was more frequent when birth weight was higher than compared with lower than 1500 g. In male infants, BAEP impairment was more frequent and more often of retrocochlear type than in female infants. BAEP impairment was more frequently of endocochlear type in female compared to male infants. Among the 89 premature infants recorded, 11.2% has endocochlear damage corresponding to potentially handicapping hearing loss. These results are discussed with reference to the literature.

Maturation of the auditory brainstem in low risk-preterm infants: a comparison with age-matched full term infants up to 6 years

Whether preterm birth has a significant effect on the maturation of the human brain remains an equivocal issue. Since experience plays a crucial role in the development of the brain, it is conceivable that extra-uterine preterm exposure could exert some effects on the maturation of the developing human brain. The present study compared the post-term maturation of the central components of brainstem auditory evoked response (BAER) in low risk preterm infants with that of age-matched full term infants up to 6 years. The preterm infants demonstrated similar maturational profiles to those of the term infants in both interpeak intervals and amplitude measures. No systematic, statistically significant differences were found between the preterm and term infants in any of the BAER variables although the I-V interval tended to be slightly shortened in the prematurely born infants. These results suggest that preterm birth or earlier exposure to sound environment extra utero is unlikely to lead to significant neurophysiological consequence in the developing auditory brainstem of low risk infants.

The epidemiology of childhood hearing impairment: factor relevant to planning of services

In the Nottingham District Health Authority we found that one in 943 babies born between 1983-1986 have a sensorineural or mixed hearing impairment (at 50 dB HL or greater in the better ear averaged over the frequencies 0.5, 1, 2, 4 kHz) that is either congenital or progressive in nature. If this figure is broken down between non-neonatal intensive care unit babies and neonatal intensive care unit (NICU) graduates, we find that one in 174 NICU graduates have a hearing impairment compared with one in 1278 non-NICU babies. Excluding from the non-NICU baby population those with a known family history of hearing impairment, and those with a known relevant syndrome at birth, there is a 10.2 to 1 odds ratio for babies in NICU to have such hearing impairments compared to this restricted 'normal' baby population. In addition NICU babies with a hearing impairment were considerably more likely to have another disability (odds ratio 8.7 to 1). Acquired sensorineural or mixed impairments comprised about 9% of the children with impairments by 3 years of age. Twenty per cent of the patients seen at the Children's Hearing Assessment Centre (CHAC) with better-ear impairment of 95 dB HL or greater had acquired hearing impairments. The mean age of referral for congenital hearing impairments was found to be a function of severity and NICU status. For children with better-ear hearing impairments of 80 dB HL or greater, the mean and median ages of referral were both 8 months (s.d. 4 months).

Comparison of female to male and male to female transmission of HIV in 563 stable couples. European Study Group on Heterosexual Transmission of HIV

OBJECTIVE

To identify risk factors for heterosexual transmission of HIV and to compare the efficiency of male to female and female to male transmission.

DESIGN

Cohort study of heterosexual couples. Regular partners of HIV infected subjects were tested and both members of the couples interviewed every six months. HIV prevalence in partners was analysed according to the characteristics of the couples.

SETTING

Nine European countries.

SUBJECTS

563 couples comprising 156 female index patients with their 159 male partners and 400 male index patients with their 404 female partners. Partners reporting risk factors other than sexual contacts with the index patient were excluded.

MAIN OUTCOME MEASURES

HIV infection in partners and high risk sexual behaviour.

RESULTS

Overall, 19 (12%) male partners and 82 (20%) female partners were infected with HIV, suggesting that male to female transmission is 1.9 (95% confidence interval 1.1 to 3.3) times more effective than female to male transmission. An advanced stage of HIV infection in the index patient (odds ratio 17.6; 4.9 to 62.7) and sexual contacts during menses (3.4; 1.0 to 11.1) increased the risk of female to male transmission and stage of infection (2.7; 1.5 to 4.9), anal sex (5.1; 2.9 to 8.9), and age of the female partner (3.9; 1.2 to 13.0 for age > 45 years) increased the risk of male to female transmission. None of the 24 partners who had used condoms systematically since the first sexual contact was infected.

CONCLUSIONS

Several factors which potentiate the risk of transmission through unprotected vaginal intercourse have been identified. Knowledge of these factors could be helpful for counselling patients infected with HIV and their sexual partners.

Reliability and effectiveness of screening for hearing loss in high risk neonates

OBJECTIVE

To establish the reliability and effectiveness of screening for hearing loss by brainstem auditory evoked potential testing in high risk neonates.

DESIGN

Seven year investigation of newborn babies admitted to a special care baby unit and monitored through a regional children's audiology unit.

SETTING

Special care baby unit and children's audiology department, Belfast.

SUBJECTS

405 neonates admitted to the baby unit, during 1 October 1982 to 31 March 1987.

MAIN OUTCOME MEASURES

Presence of hearing impairment, type and severity of hearing impairment, mortality.

RESULTS

85 children failed the screening test, 62 of whom were followed up. Five children had severe bilateral sensorineural impairment and 12 had conductive impairment requiring surgical intervention. A further 18 had severe neurological disorder detected. The sensitivity of screening was 100% and specificity was 88%. If the procedure was introduced into routine clinical practice the mean age at diagnosis for all children with severe perinatal hearing impairment would be 11 (median 1) months. The mean age at diagnosis with the health visitor screening service was 23 (19) months (difference 10 months, 95% confidence interval 6 to 16 months; p < 0.0001).

CONCLUSION

Screening for hearing loss in high risk neonates is highly reliable and cost effective. It also provides valuable neurophysiological information. Routine testing of these infants would result in over half of all children with severe bilateral perinatal sensorineural hearing impairment being identified by 2 months of age. This would make an important contribution to the habilitation of this socially, emotionally, and educationally vulnerable group.

QEEG in a public health system

For the past decade the Cuban Neuroscience Center has organized on behalf of the Ministry of Public Health of the Republic, a nationwide Program for the introduction of quantitative EEG (qEEG). This Program has involved a) development of standardized equipment for "paperless" EEG, qEEG and brain topography; b) establishment of a network of 21 laboratories of clinical neurophysiology; c) creation of the specialty of clinical neurophysiology which trains physicians from all provinces in both traditional and quantitative electrophysiological methods; d) introduction of standardized protocols for the collection of clinical and electrophysiological information; e) organization of a national normative and neuropsychiatric database; f) establishment of normative regression equations. Among the special issues discussed are: 1) relationship between traditional and quantitative methods; 2) evaluation of the effectiveness of the technology introduced; 3) use of qEEG in the early detection of brain dysfunction.

Evaluation of risk factors for hearing impairment in at risk neonates by brainstem evoked response audiometry (BERA)

Thirteen (19.2%) of 68 at risk neonates in an intensive care nursery with one or more adverse perinatal clinical factors viz; prematurity (less than 37 wks), low birth weight (less than 2000 gm), hyperbilirubinemia requiring active intervention, birth anoxia, neonatal seizures, infections, aminoglycoside administration, and craniofacial malformations; were diagnosed to have hearing impairment (elevated auditory threshold) by BERA testing performed within the first six weeks of life at a mean conceptional (gestational age + age after birth) age of 40.2 +/- 0.6 wks. As against this, 20 healthy term neonates who were examined at a mean conceptional age of 40.4 +/- 0.8 weeks had a normal hearing threshold of 30 db nHL. Elevated auditory threshold was found more frequently in neonates with multiple clinical adverse factors than in those having single risk factor (6/13 Vs 7/55, p less than 0.001). On multiple logistic regression analysis, however, only 2 factors viz; hyperbilirubinemia at level exceeding indication for exchange transfusion and birth weight less than 1500 gm, were found to be significantly correlated with the hearing impairment in the affected neonates and in that order of importance. Prematurity, birth asphyxia, neonatal seizures, infections and aminoglycoside administration had no significant correlation with hearing impairment. Since most of the neonates admitted to the neonatal ICU have one or more identified adverse risk factors, their hearing screening by BERA at the time of discharge seems justified.

Comparison of reflex modification procedures and auditory brainstem response in high-risk neonates

This study compared the results of reflex modification (RM)--an objective technique for assessing brainstem sensorineural processing--with those of auditory brainstem response (ABR) for a group of high-risk infants at comparable postconceptional ages. For the RM procedure, an eyeblink-eliciting tap to the glabella was presented either alone or accompanied by a brief 90dB SPL tone. 37 high-risk infants were tested with both RM and ABR at a mean postconceptional age of 37.3 weeks. Seven had an increased brainstem conduction time ('failed ABR') and eight did not exhibit significant reflex augmentation ('failed RM'), seven of whom also failed the ABR. These data provide evidence that sensory stimuli which affect the neural mechanisms responsible for the organization of the startle response and auditory processing share essential neural components.

Epidemiologic patterns in childhood hearing loss: a review

In an attempt to clarify international epidemiologic trends, a review of the published literature pertaining to childhood hearing loss is presented. Inconsistencies of methodology and classification, which complicate the interpretation of data and make difficult the quantification of the influence of genuine population differences, are discussed. Selective review of the literature allows certain crude statements to be made regarding childhood hearing loss. In developed countries, serous otitis media is the most common cause of hearing loss in children, affecting up to two thirds of preschool children. In addition, 1.0-2.0/1000 children have bilateral SNHL of at least 50 dB. In underdeveloped countries, suppurative middle ear disease is common and is still frequently associated with either an intratemporal or intracranial complication. SNHL appears to occur almost twice as often as in developed countries, with a greater proportion being of infectious etiology. In specific populations, the Inuits, Amerindians and Aboriginals, acute and chronic suppurative otitis media are almost endemic, yet both cholesteatoma and serous otitis media are uncommon.

Consistency and changes in the development of extremely low birthweight infants

Thirty infants who weighed less than 1,000 g were evaluated as to neurological functioning and mental ability at 1 year and, again, at 3 years of age. The results of the examinations showed the high correlation in the neurological status between infancy and the preschool period, particularly, for children who were diagnosed as being clearly normal or abnormal at 1 year. There was a high percentage of psychomotor delays in those with ophthalmic complications.

Electrophysiologic assessment of auditory pathways in high risk infants

This study evaluated auditory processing in a group of 59 infants at risk for subsequent hearing and language disorders due to low birthweight and/or perinatal asphyxia. Auditory system integrity was evaluated electrophysiologically by recording the auditory brainstem response (ABR), middle latency response (MLR) and the cortical auditory evoked potential (CAEP). 63% of the babies had normal peripheral function or slight unilateral impairment; 84% had normal brainstem auditory system function; 82% showed normal MLRs; and 81% showed normal CAEPs. Fifty-three percent of the babies were normal on all tests and only 3% were deviant on all tests. The remaining infants showed diverse patterns of peripheral, brainstem and cortical abnormalities.

Brainstem electric-response audiometry in infants of a neonatal intensive care unit

Brainstem electric-response audiometry was used to assess the auditory function of 600 infants from a neonatal intensive care unit. Two groups of children were tested, one group as inpatients prior to discharge with a mean age at test of 39.4 weeks and one group as outpatients with a mean age at test of 55.4 weeks. Our results indicate that testing infants when they are older will reduce the incidence of failure on the initial evaluation and will reduce the identification of transient hearing losses which resolve spontaneously. Our results also indicate that a threshold of 30 dB nHL or less is probably normal and that some infants with a threshold of 40 dB nHL at first test require otological or audiological management.

Screening for auditory dysfunction in high risk neonates

Brainstem auditory evoked responses were recorded in 117 pre-term and 71 full-term infants from the general population of infants born at a referral obstetric unit. The threshold intensity required to evoke a reliable BAER was determined at different post-menstrual ages (PMAs) and in many cases at follow-up clinics. The BAER thresholds for 12 infants born and tested at less than 31 wk PMA were all greater than or equal to 50 dBHL. Sixty-two low-gestational-age infants who were tested between 31 and 36 wk PMA had BAER thresholds between less than or equal to 30 dBHL and greater than or equal to 80 dBHL. The majority of pre-term and term infants tested at term equivalent age had BAER thresholds less than or equal to 30 dBHL. Longitudinal studies also indicated that BAER thresholds can decline rapidly during the pre-term period. Follow-up studies showed that those pre-term and term infants with BAER thresholds less than or equal to 30 dBHL had normal auditory thresholds as determined using conventional behavioural testing at 4 or more months of age. Of those infants with BAER thresholds greater than or equal to 40 dBHL at the time of discharge or at term equivalent age, 67% (n = 16) were confirmed later as having a moderate to profound hearing deficit. The remaining 8 infants in this group had had BAER thresholds at term of 40 or 50 dBHL and had normal BAER and behavioural thresholds at follow-up. The cross-sectional and longitudinal data indicate that the majority of low-gestational-age infants who are at risk of hearing deficit achieve BAER thresholds less than or equal to 30 dBHL by term equivalent age. We recommend that auditory screening of infants in this group is best performed at the time of discharge from hospital or at term equivalent age, whichever is the later. Those infants with thresholds greater than or equal to 40 dBHL at that time should be encouraged to attend follow-up testing and, if high thresholds persist, they should then be referred on for behavioural testing and assessment for habilitative support.

Maturation of the brain-stem auditory evoked potential in premature infants

Patterns of development and extent of variability of the brain-stem auditory evoked potential (BAEP) are described in 52 healthy premature infants and 50 normal term newborns with reliable conceptional ages. Binaural and monaural stimulation are compared. Serial studies of individual prematures are emphasized and demonstrate that the most consistent and least variable measures are the monaurally derived interpeak intervals. All the BAEP parameters studied mature including wave form, relative amplitude, peak and interpeak intervals, but there is far more variability in preterms than in term infants or adults, even when infants are carefully matched for conceptional age. As term is approached, BAEP variability decreases substantially, suggesting that near term the BAEP becomes a more reliable indicator of neurologic function. The variability of the BAEP in the normal preterm limits its usefulness in determining neurologic dysfunction in individual high risk infants. Nevertheless, the BAEP may still prove useful for defining group differences among infants and could provide an objective measure of those factors influencing neurologic development. Serial change in the BAEP is a specific parameter which we believe merits further study in premature infants as an index of neurologic maturation.

Prognostic validity of auditory brainstem evoked response screening in newborn infants

The effectiveness of the auditory brainstem evoked response (ABR) test as a screening test for permanent hearing loss in neonates is examined in 32 published studies including 4,945 infants. Follow-up studies validating initial test failure were available for only 658 infants. Significant differences in methodology exist among these studies, and these differences may have affected their outcomes. Despite this problem, data from these studies were pooled, and they revealed that 16.5 per cent of neonates failed the initial ABR test. Of these, 5.1 per cent were later confirmed to be hearing-impaired or otherwise neurologically impaired. This implies that many of the false-positive results occurred in neonates who had transient disorders, such as conductive hearing loss or neurologic abnormalities, at the time of the screening test, or that the pass/fail criterion was too stringent. Lack of data on false-negative results or the rate of correct identification of normal infants makes it impossible to assess the sensitivity of the test accurately. Firm estimates of the prognostic validity of the neonatal ABR screening in identifying the impaired population can be achieved only when the actual impairment rate can be estimated, and when the distributions of ABR latencies and thresholds for both normal and impaired populations are known. These data could be obtained by following groups of high-risk infants longitudinally and by pooling raw ABR data from the normal and impaired populations that are collected using standardized procedures and similar equipment.

Auditory brainstem response in infant hydrocephalus

Fifteen infants with hydrocephalus ranging in age from 32 to 43 weeks from conception were studied. The auditory brainstem response (ABR) was measured 48 h prior to the placement of a CSF shunt and within 5 days following shunt insertion. Results of this study showed a general improvement in the ABR following placement of the shunt. No consistent patterns were observed that allowed a clear explanation of the cause and effect of the abnormal ABR. However, the changes seen in the ABR are caused by increased CSF pressure, which may compress the transmission fibers, and generators of the ABR producing a type of neuropraxis. Early shunting appears to have a better outcome on the ABR than later shunting.

Follow-up of infants screened by auditory brainstem response in the neonatal intensive care unit

Auditory brainstem response screening at 40 and 60 dB was conducted in 100 infants in the neonatal intensive care unit to determine initial failure rate and prevalence of abnormality on follow-up. Of our NICU population, 20% failed one or both of the screening levels: 9% failed at 60 dB in both ears, and 11% failed at 40 dB in one or both ears. On follow-up, half of the 60 dB failure group were found to have sensorineural or conductive impairment and represent the 2% to 4% prevalence of serious otologic-audiologic problems generally found in an NICU population. Subsequent improvement (reversal) of the retest ABR records of the remaining infants in the 60 dB failure group was thought to be related to neural changes in the brainstem associated with recovery from hypoxic episodes. A transient or reversible conductive deficit appeared to account for the majority of failures at 40 dB. We recommend the screening protocol be expanded to include threshold and latency measures in infants who fail the initial screening. The transient nature of many ABR abnormalities makes postdischarge ABR, otologic, audiologic, and neurologic examinations mandatory before any inferences are made about hearing loss or neurodevelopmental disorders.

A comparative study of measurements of SN-10 and the 40/sec middle latency responses in newborns

Auditory SN-10 responses and summed middle latency responses (40/sec MLR) were obtained from 36 full-term newborns. Wave V latencies from 20-70 dB nHL were in agreement with previous studies. Although the amplitudes of the SN-10 and the 40/sec MLR paradigms were not significantly different, we were able to detect the lowest thresholds with an SN-10 response for unfiltered clicks. The mean threshold for the click evoked SN-10 potential was 5 dB better than the mean threshold for the click evoked 40/sec MLR and 10 dB better than the mean threshold for the 500 Hz toneburst 40/sec MLR. We conclude that both the SN-10 and 40/sec MLR techniques can be useful in the assessment of the hearing of newborns, but that only the 40/sec MLR may be useful in obtaining responses to a 500 Hz toneburst.