Infant Hearing Screening - Essay Example

 Otoacoustic Emissions and Auditory Brainstem Response in Relation to Newborn Hearing Screening Test Article: A Model of Two-stage Newborn Hearing Screening with Automated Auditory Brainstem Response by Satoshi Iwasakia, Yasuhiro Hayashi, Atsurou Seki, Mituyoshi Nagura, Yasuyuki Hashimoto, Goro Oshima, Tomoyuki Hoshino Summary Previously, hearing loss in infants used to be detected between 18 and 24 months. And then it usually took over 48 months to detect mild or moderate hearing loss in child. Obviously, intervention at the late age did not bring any favourable desired results. In 1993, the National Institute of Health recommended for hearing test in the infants within 3 months of birth. As such, there are many procedures that are employed for hearing test but two commonly used tests are: Auditory Brainstem Response and Otoacoustic Emissions (OAE). Earlier, the proportion of reported false-positive cases in hearing screening were found to be at 2.5-8% of all screened cases and such a large proportion of false cases were causing not only emotional distress to the parents but also a lot of inconvenience too. Overtime, it became necessary to have a more reliable newborn hearing screening programme. In a two stage screening program, OAE method is employed as a first stage followed by AABR. Alternatively, infants from first-stage AABR are subjected to another AABR screening to eliminate the levels of false-positive cases and detect true cases where of hearing loss at early age in infants. To find the reliability and efficiency of a two-stage AABR screening test, researchers conducted a study that involved 4085 newborn infants. During January 2000 to December 2001, two hospitals namely Seirei-Hamamatsu General Hospital and Seirei-Mikatahara General Hospital in Hamamatsu city were chosen for the study. Hearing screening was performed by trained people using an ALGO 2e AABR screener. The screener could screen the left and right ears at the same time. Infants were tested during their sleeping state after obtaining their mothers' consent. First screening test was done with AABR within 2-3 days of infants' birth. Again, for the referred cases, re-screening test was performed after 5-6 days of birth. Further diagnostic work-up such as ABR, OAE, and a conditioned orientation reflex (COR) audiometry was done within the age of 3-6 months at Hamamatsu University Hospital and Seirei-Hamamatsu General Hospitals. Clinical data so collected were analyzed to ascertain the findings. In all, 4085 infants were tested using AABR and 49 infants were referred after the initial AABR screening and they all were performed re-screening test using AABR. Of the 49 infants referred, twenty-nine were re-referred in the screening test. And hearing loss was detected in 15 of the infants. Out of these 15 infants, eight were detected with bilateral failure; five of these had moderate haring loss and three had severe hearing loss. Seven of the infants had unilateral failure. The false-positive cases were reported in 34 infants out of the total 4085 infants who had undergone initial hearing screening. In percentage terms, this was estimated as 0.83 percent; however, this got reduced to 0.34% in the two-stage infant hearing screening. OAE and AABR, both are the methods that are used for infant hearing screening. The OAE method rests on measuring sound waves that are generated in the cochlea by placing miniature microphones in the external ear canals. Though OAE screening is easier and quicker to perform compared to ABR, it is influenced by ear wax or fluid. AABR is not affected by fluid or ear wax and much lesser referral rate (3-4%), relative to OAE, is noticed with AABR screening using the ALGO 2e screener. It is worth noting that referral rate with OAE screening alone is as high as 21-43%. At some centers, to increase effectiveness of screening process, first OAE test is performed at the maternity ward and OAE retest is performed after 3 weeks. In these cases, the referral rates from first and second OAE screening tests were found to be 1.4% and 0.3% respectively. Authors argue that in one of the recently published study, two-stage AABR screening test reported much lower false-positive rate of 0.8%. Moreover, first AABR and the subsequent retest had referral rates of 4.17 and 1.01% respectively. In contrast, the study under discussion, the false-positive rate with two-stage screening protocol was found to be only 0.34%. Not only false-positive rates but also referral rates were found to be low when compared with other reported data. If on one hand, false-positive test leads to discomfort to the parents then at the same time, false-negative test too creates a false-sense of security. It becomes essential that more reliable methods are employed for new-born hearing screening so that undue anxiety on parts of parents is lessened due to false-positive reporting. Cytomegalovirus (CMV) infection to the infant is one of the causes of early onset of hearing loss and ABR screening protocol is better equipped to detect it; however, late onset of hearing loss due to CMV infection is an issue for new-born. To address the issue, the National Institute on Deafness and Other Communication Disorders (NIDCD) recommended conducting CMV Screening along with hearing screening in infants. It can be concluded that two-stage screening test employing ABR leads to a lower false-positive and referral rate; however, other factors such as nursery room, trained worker, the time gap between the two-stages in screening and the conditions of the infants are equally important in correct diagnosis. Researchers concluded that two-stage screening of AABR is not only time efficient but effective too due to considerable decrease in the false-positive cases as well as referral rate. Article: Screening for Hearing Loss in Childhood: Issues, Evidence and Current Approaches in the UK by John Bamford, Kai Uus, Adrian Davis Summary The article speaks about newborn hearing screening programme (NHSP) and the childhood hearing issue in the UK. At least until 2000, screening for childhood hearing loss in the UK was conducted only at eight months or at age four or five when child usually entered school. Authors argue that bilateral hearing loss in the UK is found to be about 1.1 per thousand births and major factors behind this debility are craniofacial anomalies, a family history of permanent childhood hearing loss and a neonatal intensive care lasting more than 48 hours. At least 60 percent of cases will have one of the risk factors as mentioned above. The hearing disability impacts severely on child's development, communication ability, academic achievement or literacy, emotional and social well-being and on employment opportunities. Hearing disability can be improved dramatically, if medical intervention is done within six months of birth of a newborn. It was soon recognised that detecting permanent hearing loss at age five or beyond cannot help much in restoring or bringing back lost hearing of the child. The distraction test screen done at this age is not effective as it used to refer large case, as high as 10% on national level. Meanwhile, technological advances have developed equipments that could be deployed to measure electrophysiological activity through auditory pathways. The procedure known as the auditory brainstem response (ABR) is based on automated pass/fail decision criteria; that has made it possible to screen newborns to identify bilateral permanent hearing loss. Based on the recommendation of National Screening Committee, the NHSP programme began in England in 2001. The screening consists of two tests: The first test is Automatic Otoacoustic Emissions (AOAE) and the second one is called automated Auditory Brainstem Response (AABR). If both ears give satisfactory AOAE responses then baby is said to have passed the test and no further test is then necessary. Further, babies from neonatal intensive care units for more than 48 hours are done with both tests. The effectiveness of NHSP programme was evaluated in 2004 in reference to screen performance, maternal anxiety and satisfaction, experiences of parents, follow-up of screen referrals by audiology department, impact of the NHSP on services, and cost-effectiveness. The babies failed to give bilateral responses to hearing screen were referred for audiological assessment. Babies were tested for ABR and middle ear function testing to detect middle ear pathology. Bilateral hearing loss was measured at 1.0 per 1000 babies screened with 95 percent confidence interval, which matched with the expected rates of hearing issues. Screen protocol aimed at referring babies with hearing defects in single as well as both the ears. Because of this, a significant number of babies were identified with hearing loss. Unilateral hearing defect cases were found to be 0.64 per 1000 at 95 percent confidence interval. On implementing NHSP, the median age of detecting bilateral hearing loss got reduced to 10 weeks and most of the cases were detected within 6 months of birth. Early identification of hearing defects in newborn facilitated medical intervention for corrective action. Appropriateness of OAE and ABR in Relation to Newborn Hearing Screening Ever since newborn hearing screening programme (NHSP) has been implemented in the UK, it has been a most important question of discussion as to which technique is the most appropriate one for newborn hearing screening. The health visitor distraction test (HVDT) screening programme that was employed in the UK during 1990s had major disadvantage in that it could not be done until 6 months of infant life. Moreover, it was also endowed with high false positive rate. Subsequently, with the emergence of automated auditory brainstem response (AABR) and the OAE technique, increasing number of hospitals are now opting for these techniques or some combination to thereof. It is worthwhile to note that none of the device measures hearing directly. Both the devices are associated with measuring different physiological mechanisms. Algo 2 machine employs 35 dB nHL click; that means children with mild sensory hearing loss in the region of 25-30 dB would perhaps be missed by this device. Contrary to this, OAEs will detect hearing at 25dB. Algo 2 is a device that cannot give frequency specific information; it just confirms hearing loss and its characteristics (Owens et al 2000). OAE has been the most commonly used method to measure hearing defects in newborn before discharge. It has been found that health vendors (HVs) can perform neonatal hearing screening with high coverage rates in the given time frame. HVs also agree that the procedure save them a lot of time. Due to availability of new hand held OAE devices such as Echosensor or Echocheck, the feasibility of community based screening has increased. The major disadvantage with OAE is that it may give false positive result during first 24 hours of birth, therefore ideal age is to conduct OAE test only after at least one day of life but the difficulty lies in the sense that usually babies are discharged within first 24 hours of birth. For example, the rate of discharge at North London maternity unit in the first 24 hours is as high as 48 percent and at Royal Hospital maternity unit at Gloucestershire the discharge rate is 28 percent. While looking at advantages with the OAE, the technique is relatively easy to grasp and machines work based on pass/fail criteria so that observer error is largely avoided. Moreover, OAE does not need any specific qualification on part of the technician (Owens et al 2000). OAE based hearing screening programme detects congenital hearing defects in the babies at the cochlear level; however, a small number of babies may have hearing defects due to brain stem, auditory nerve or cortex defect. These are associated with other issues such as low birth weight, extensive neonatal intensive care, premature birth, neonatal infections, perinatal asphyxia, convulsions, and high levels of bilirubin. Usually they are small in percentage and need to be referred for further screening through automated auditory brain stem responses (AABR). OAE testing has high false positive rate of 15.6 percent during first 24 hours that goes down to almost 4 percent in 72 hours. Mostly, these are associated to debris in the external ear canal and middle ear effusion issues. Neurological immaturity is also another reason. The first test pass rate is found to be as high as 95.7 percent for unilateral hearing and 92.7 percent for bilateral passing that goes up to 97.7 percent after the second test; however, factors such as fluid, debris or wax in the middle or external ear do cause sustained inhibition to the OAE response (Owens et al 2000). Johnson et al (2004) argue that 2-stage OAE/ABR is a better solution because referral rates at time of discharge is much lower from such protocols when compared with only OAE screening. At some quarters, concerns are raised about infants who do not pass OAE but eventually clear ABR test; it is quite likely that such infants may have some mild loss of hearing that is not detected by ABR. To address the issue, the study was designed to find those cases of infants where they failed OAE test but passed the ABR in 2-stage hearing screening test and then, subsequently, they were found with permanent hearing loss (PHL) at age 9 months. The study revealed that a significant proportion of infants found to have permanent hearing loss (PHL) at age 9 months were not detected by a 2-stage OAE/ABR hearing screening protocol. It was found that around 23 percent of infants with PHL >25 DB passed the ABR though they had mild hearing defects. Researchers argue that many factors can be responsible in detecting the infants with PHL by 9 months of their age. To counter this lacuna, it is required that a stimulus for testing in a 2-stage OAE/ABR screening protocol is set at 25dB instead of 35 dB. This will result into higher level of referral with lesser number of infants passing the ABR screening. It is important to note here that OAE screening test measures the sound pressure level in the ear canal and therefore, the intensity level of the signal will remain constant for each infant regardless of ear canal size. In case of ABR, the actual sound pressure level at the eardrum differs considerably from infant to infant. Perhaps, this could be the reason why screening fails on OAE but passes with ABR with some infants. Moreover, currently, no standard methods are available for calibrating ABR and OAE test devices, hence difficult to describe its impact (Johnson et al (2004). A woman who has acquired CMV infection any time in the past may transmit the infection to fetus and can result into sensorineural hearing loss (SNHL). This is important in the sense that congenital CMV infection in the UK account for about 15% of SNHL. Antenatal screening to detect women infected with CMV is a good way to check its transmission to the infants. Moreover, 5-10% of infected infants who do not show any symptoms in the neonatal period have been found to have CMV related issues on follow up and hearing loss is the most unfavourable and progressive outcome of CMV infection. Primary maternal infection is the major reason for fetus infection hence it becomes essential to know about maternal infection so that further screening for fetus infection could be carried out. A newborn with IgM antibodies will indicate about congenital CMV infection. It should be noted that negative blood results do not necessarily negate CMV infection as virus could be in very low numbers. For the cases of congenital CMV infection in the infants, audiological assessment is required every three months to know about the changes in hearing status of the infant and to take necessary corrective action (Ross & Fowler, 2008). Above studies establish that appropriateness of OAE and ABR methods for hearing screening needs to be evaluated very carefully based on infant age and several other factors under given circumstances. References Bamford, J., Uus, K., Davis, A. (2005). Screening for Hearing Loss in Childhood: Issues, Evidence and Current Approaches in the UK. Journal of Medical Screening. Volume 12, Number 3, 119–124 Iwasakia, S.; Hayashib, Y.; Sekic, A.; Naguraa, M.; Hashimotoa, Y.; Oshimaa, G.; Hoshinoa, T. (2003). A model of two-stage newborn hearing screening with automated auditory brainstem response. International Journal of Pediatric Otorhinolaryngology, 1099-1104. Johnson, J.L.; White, K.R.; Widen, J.E., Gravel, J.S.; James, M.J.; Kennalley, T.; Maxon, A. B.; Spivak, L.; Sullivan-Mahoney, M.; Vohr, B. R.; Weirather, Y.; and Holstrum, J. (2004). A Multicenter Evaluation of How Many Infants with Permanent Hearing Loss Pass a Two-stage Otoacoustic Emissions/Automated Auditory Brainstem Response Newborn Hearing Screening Protocol. American Academy of Pediatrics. [Online] Available from http://www.infanthearing.org/ncham/publications/Pediatrics%20Article.pdf [accessed 10 January, 2013] Owen, M. Webb, M. Evans, K. (2000). Community based universal neonatal hearing screening by health visitors using otoacoustic emissions. ADC Fetal & Neonatal. [Online] Available from http://fn.bmj.com/content/84/3/F157.full.html#ref-list-1[accessed 10 January, 2013] Ross, D. S. & Fowler, K. B. (2008). Cytomegalovirus: A Major Cause of Hearing Loss in Children. The Asha Leader. [Online] Available from http://www.asha.org/Publications/leader/2008/080506/f080506b/ [accessed 12 January, 2013] Read More