During the first years of life, children depend on their senses to obtain experiences which will be important for their social and psychical development. In relation to hearing sensitiveness, the physiological-anatomy integrity of the hearing system is fundamental to normal oral language acquisition and development. According to Carvalho (1994), hearing loss, even being light, can alter oral communication development (1).
Previous identification of hearing alterations can interfere on "critical" and ideal period of language and audition stimulation. Maturity process of central hearing system occurs during the first years of life. Hearing experience during larger cerebral plasticity period, when new neural connections are settled, is essential to guarantee language and audition development. (1,2).
In physiological terms, hearing receiver structure is composed by supporting cells and ciliated cells - Corti organ. External ciliated cells do not work as cochlear receiver, so they do no codify sonorous message. They are capable for two types of contraction, quick and slow, and are active cochlear effectors due to electromotility, i.e. biomechanical properties (3).
External ciliated cells composed cochlear amplifier. They are important for the stimulus amplification mechanism in order to determine the functioning of the internal ciliated cells, what would be the cochlear receiving and codifying units and would work as an important role on frequency selection of the cochlea (4).
Such cells are responsible for otoacoustic emissions due to mechanical energy released on quick contraction. Otoacoustic emissions are energy responses from audio frequency of cochlea arising from external ciliated cells, which can be received by a sensitive miniature microphone when acoustic stimuli are applied as clicks on external auditory canal. This energy that is released on cochlea is transmitted by ossicular chain and tympanum membrane to external acoustic meatus, where it can be registered. These responses are due to an active biomechanism from external ciliated cells. Electric-induced quick contractions occur in the absence of ATP (Adenosine triphosphate) and presence of low level of calcium, disproving a role of contractile protein (5).
Otoacoustic Emissions (OAE) are sonorous energy of weak intensity which are amplified by contractions of external ciliated cells in the cochlea and can be received on external acoustic meatus. They were found by professor David T Kemp from University College - London in 1998. They can be classified as: spontaneous, if in external acoustic meatus in the absence of acoustic stimulation; evoked, when there is energy liberation in external acoustic meatus in response to an acoustic stimulus. Evoked OAE are classified as: transitory - evoked by brief acoustic stimulus of ample spectrum that cover a range of frequencies - click or tune burst; distortion product - evoked by two clear tunes (F1 and F2) that produce as response a distortion product by intermodulation (2F1 - F2); stimulus-frequency - evoked by a continuous sound of weak intensity in frequency of the presented stimulus; are less used in clinical terms (4).
OAE method is simple, of quick accomplishment, can be applied during sleeping time, it does not require sedation or placement of electrodes to do the exam. OAE, though, presents larger number of false-positive when compared to Auditory Evoked Potential (BERA), specially in the first 48 hours of life (6,7,8).
Auditory Potential (BERA) is a high sensibility test which does not require voluntary response. Electrodes are placed on the child scalp, requiring sedation most of times, and should be meticulously recommended on neonatal period. Therefore, false-positive results have been recorded in newborns with normal hearing (9).
For all that, the National Institute of Health (NIH) establishes that newborn hearing screening should be done with OAE and the negative cases should be submitted to a second confirmatory screening with BERA. The recommended universal newborn hearing screening starts with OAE and conclusions are: all newborns with positive results are released from hospital; all of those with negative results undergo to another screening on BERA; non-confirmed cases on BERA are submitted to new exams during the first six months, and the confirmed cases will come for another visit to assure the presence of deafness, type and degree of hearing implication (9).
OAE can be recorded not matter sex or age, in most of individuals who present normal hearing. PROBST (1990) mentions prevalence of OAE in 98% of adults with normal hearing. KEMP et al. (1991), JOHNSEN et al. (1988) and BONFILS et al. (1988) support that OAE is detected in newborns in the same percentage.
When Newborn Hearing Screening makes use of OAE device, it presents neither any risk nor damages to physical, mental and social health of the child and its parents/responsible people. The benefits include the possibility of a precocious diagnosis and treatment, providing better prognosis to patient, because it reduces the possibility of damages on language acquisition by the NB. This is good for the population, as it improves social insertion of the child.
This study aims to measure the prevalence of hearing impairment in NB from Bárbara Heliodora Maternity Hospital using DPOAE (distortion product otoacustic emissions), from November 2004 to January 2005, considering that in the state of Acre and the North of the country there are no records of Newborn Hearing Screening. MATERIAL AND METHODS
This study was done at Bárbara Heliodora Maternity hospital Rio Branco - Acre, after parents and/or responsible people having authorized by signing a free and clear consent and approval term from Comitê de Ética em Pesquisa of FUNDHACRE (Research Ethics Committee).
Such maternity was chosen for being a reference one, though public, for pregnant women from Rio Branco.
The inclusion criteria were:
- NB aging from 0 to 28 days;
- born at Bárbara Heliodora Maternity;
- both boys and girls;
- permission from responsible people after signing a free and clear consent and approval term.
Patients not included:
- Infants aging over 28 days of life;
- Not born at Bárbara Heliodora Maternity;
- Born out of the established period for the study;
- Having not agreed signing the term.
The sample is composed of 200 children, 50 males and 50 females. Six of them had family history of hearing impairment. From those one case had more than one relative with it. Only one child presented congenital malformation.
The responsible people for the NB had to answer a questionnaire done by the author of the study and the interview was done a speech doctor, the author and medical students involved in the Project. After that all NB were submitted to otoscopy with HEINE device.
The distortion product otoacustic emissions test was done with Maico®
and printer (1). A probe is placed on external acoustic meatus, which is the critical point to otoemissions, followed by a result record in the same device. In order to better protect the probe, an olive (sealing device) is placed in its extremity, helping sealing external acoustic meatus. Correct placement of the probe is essential in order to a uniform stimulation of the cochlea and consequently to OAE achievement. If probe presents leaking, it is caused noise entrance (NB or environment) and things darkening OAE.
Picture l - Otoacoustic emission device and printer.
This device was chosen because of its easy handling and trust on results. It is a type of probe using four batteries AA, printer with batteries, external feeding via cable, phone, monitor and olive set "replacement probe tips" (1), with otoacoustic emissions by distortion product and transient in 6 frenquencies.
NB was tested after been fed, and preferably being sleeping, considering that any movement can displace the probe on acoustic meatus, causing goods interference. The test took place in calm and quiet place, whenever possible, though not always in common area.
The exam result was analyzed and given to Bárbara Heliodora Maternity in order to be attached to the form the day after the test done. A copy of the exam was given to parents/responsible people.
When NB failed DPOAE test (possible deafness), another screening with Auditory Brainstem Response (ABR) was appointed, done at Fundação Hospital do Acre (FUNDHACRE) - Otorhinolaryngology Service in 90 days, under the responsibility of the author of the study.
All children with audiological deficit assured by Auditory Brainstem Response should be followed in the ambulatory at Serviço de Otorrinolaringologia da FUNDHACRE (Otorhinolaryngology Service) during the first months of life, with the purpose of solution or improvement of their hearing problem through prosthesis use (Devices of Individual Sonorous Amplification) or through being led to more advanced centers to cochlear implantation. Both treatments are financially supported by SUS - Sistema Único de Saúde (Public Health System).
In relation to variables, hearing acuteness presented as a dependent variable, before Newborn Hearing Screening. Result: failed (hearing impairment), succeeded (lack of impairment) and not clear or not conclusive. As independent variables, relatives with hearing disorder, preterm labor and low-weigh NB (< 2500g).
The data gathered from epidemiological forms were transferred into spreadsheets and statistical analysis was done using SPSS "for WindowsÒ" 12.0. It was used descriptive analysis with simple and relative frequencies displayed in tables and in the text itself to results description. RESULTS
From the 200 NBs examined, only one (0.5%) presented altered Evoked Otoacoustic Emissions (DPOAE). Non-conclusive or non-trustful results did not occur. The child was 20 days of life when the exam was performed, weighing 1.515g, born by transvaginal preterm delivery and any congenital malformation had not been diagnosed up to the moment of the exam. These and other information from this NB with alteration on DPOAE is displayed in Table 1.
In 33 cases (16.5%) there was a record of perinatal hospitalization. The main reasons were: hemorrhage (n=8; 24.2%); pain in prelabor stage (n=5; 15.1%), malaria (n=3; 9%) and urine infection (n=3.9%). Only 19 mothers (9.5%) referred disease during pregnancy. Mother´s average age was 23.34 ± 6.26 years and father´s was 27.87 ± 8.72 (Table 2 and 3).
Only 37% of them (n=74) reported more than six prenatal consultation, while 14 mothers (7.0%) did not before labor. Nearly half (48%) of the labors were caesareans. Children aging from 0 to 20 days of life were examined. Their average age was 1.13 ± 2.05 (medium = 1 day). NB average weight, in the moment of the evaluation, was 3122.31 ± 588.4g, raging from 1.085 to 4.900g (Table 3). Half of the cases (50%; n=100) were male.
From the cases (n=66) in which Apgar evaluation in the 1st minute was performed, 4 of them (6.1%) scored lower or equal 5. And among the ones evaluated in the 5th minute (n=66) one of them (1.5%) presented Apgar lower than 7 (Table 4). Only one child (0.5%) presented congenital malformation. DISCUSSION
The prevalence of hearing deficit in NB, observed at Bárbara Heliodora Maternity, was 1/200 similar to the ones found in the literature.
The occurrence of deafness in babies is greater than other pathologies evaluated as screening. Comparing to other universal screening diseases, such as phenylketonuria (0.07/1.000), congenital hypothyroidism (0.17/1.000) and falciform anaemia (0.20/1.000), we have justifiable excuses for a settling of a hearing screening program.
It is said that in Brazil from 3 to 5 in 1000 children are deaf since birth. This number can raise from 2 to 4 in 100 NB when proceeding from ICU (14,15). About 50 to 75% of hearing impairment can be detected in the nursery ward through hearing screening (Otoacoustic emissions). From 7 to 12% in all NB has at least one risk factor to hearing impairment. Risk NB, which is 2.5 to 5% are moderate or severe hearing impairment carrier (SBORL, 2005).
In this study, from the 200 NB examined, only one presented altered OAE. It was premature, gestational age between 31 to 35 weeks, low weight (1.515g), few hospital visits from mother during prenatal period, no previous serology record, proceeding from ICU.
Mother of the studied children presented a figure of 37% from 6 or more consultation during prenatal period. Quality was precarious due to lack of serology and vaccine and also because of a high number of neonatal hospitalization. The current author had some difficulties such as sending mothers from one hospital to another and lack of APGAR records in NB forms (no APGAR in 67% of the forms).
There was neonatal intercurrence in 15.5% of the NB. This can be understood by the patients´ profile with an unsuitable perinatal assistance and/or by the fact that Bárbara Heliodora Maternity is a high risk one. This is the higher rate in Brazil.
The profile of the studied subjects does not differ from most people of the North part of the country. This shows once again the need of preventive procedures and assistance to mother-child.
It is necessary to do a diagnosis in failed cases after hearing screening, even if it performed in the maternity. It is indispensable that the other exams such as brainstem audiometry, impedance tests and behavior watching, are joined to otoacoustic emission test so that hearing impairment diagnosis is concluded (16).
Otoacoustic emission exam shows only external ciliated cells of cochlea and does not eliminate the chances of retrocochlear disease in normal-resulted patient (17). Thus, despite the prevalence of hearing loss found in the studied subjects is similar to the literature, it might be underestimated.
Screening together with otoacoustic emissions shows lower number of false-positive (children who failed screening, but hearing loss is not reported) and false-negative (children who succeeded screening and but hearing loss is reported later). When a test shows a high number of false-positive, the possibility of a hearing loss can cause discomfort to parents and even worse, a bad interaction between parents and child. In the same way, the false-negative can delay the diagnosis and present opposite result from the expectation with the purpose of a neonatal hearing screening. Both cases can cause an unfavorable shock for the cost-benefit relation from a program of precocious identification of impairments (18).
The methods used in order to evaluate hearing are the ones recommended by American Academy of Pediatric (AAP) and they are also used as tracking in neonatal ICU. AAP recommends first assistance to risky NB to deafness, when universal screening is not possible, and gradually the exam application to the others, even knowing that if only risk patients are tracked, 50% of the cases will not be diagnosed (19,17).
Neonatal hearing impairment should not be taken as definite, though as some alterations diagnosed in this period can improve along years others can arise (20). CONCLUSION
1. Prevalence of hearing deficit in the studied subjects was 0.5% estimating 5/1.000 born-alive babies.
2. Studied subjects had improper prenatal in quality and quantity terms;
3. Low record of exam in the labor room;
4. Implementation need of protocol of neonatal hearing screening. BIBLIOGRAPHY
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1. Master in Medicine and Health by Universidade Federal da Bahia (Federal University) - ENT doctor
2. PhD in Neonatology of Faculdade de Medicina da Bahia - Universidade Federal da Bahia (Medical School - Federal University) - Titled Professor - Doctor of Neonatology of Faculdade de Medicina da Bahia (Universidade Federal da Bahia)
3. Phaudiologist from Clínica Santa Lúcia LTDA (Santa Lucia Clinic)
4. Graduation Student from Faculdade de Medicina da Universidade Federal - Acre (Medical School of Federal University)
5. Graduation Student from Faculdade de Medicina da Universidade Nilton Lins (Medical School from Nilton Lins University)
6. Graduation Student from Faculdade de Medicina da Universidade Nilton Lins (Medical School from Nilton Lins University)
Universidade Federal da Bahia (Federal University - Bahia)
Carlos Augusto Beyruth Borges
Address: Rua Pêssego número 25 Bairro Morada do Sol Rio Branco - Acre Cep: 69910220.
This article was submitted to SGP - Sistema de Gestão de Publicações (Publication Management System) from RAIO on January 9, 2006 and was approved on February 4, 2006 22:30:22.