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J Am Acad Audiol 2 : 18-23 (1991) Pediatric ABR Screening: Pass-Fail Rates in Awake versus Asleep Neonates Stephan McCall' John A. Ferraro' Abstract The auditory brainstem response (ABR) is commonly used as a neonatal hearing screening tool . The degree to which myogenic and/or movement artifact can confound the ABR in neonates, and the effect this has on screening pass-fail rates, although widely recognized, have not been reported . This study addressed these aspects in a clinical setting . Fifty-two high-risk neonates were screened in various states of activity (asleep, awake-calm, awakeactive) . Pass-fail rates between asleep and awake babies were significantly different (p < 0.5), with the awake group displaying a much higher failure rate . There was no significant difference between the awake-calm and awake-active groups . Results indicate that activity state should be noted and considered along with the other factors that are generally blamed for false-positive results in neonatal ABR screenings . Key Words : Auditory brainstem response (ABR), pediatric, screening, pass-fail rate, asleep, awake-calm, awake-active ecording of the auditory brainstem response (ABR) is the most common R electrophysiologic technique used in the screening of neonates and infants for hearing loss (Schulman-Galambos and Galambos, 1979 ; Hyde et al, 1984 ; Shannon et al, 1984; Durieux-Smith et al, 1985 ; Fria, 1985 ; Ruth et al, 1985 ; Richmond et al, 1986 ; Jacobson and Jacobson, 1987 ; Hall et al, 1988 ; Gorga et al, 1989) . Despite its widespread use, the ABR, like all screening tools, is not infallible . There are several technical, procedural, and subject-related variables which, working together or separately, may produce false or misleading results (Fria, 1980 ; Moore, 1983 ; Weber, 1983 ; Jacobson, 1985 ; Swigart, 1986 ; Gorga et al, 1989) . Middle ear disorders, maturation of the brainstem response during the first 2 years of life, collapsing ear canals, and ambient acoustical and/or electrical noise in the testing environment are examples of factors that may lead to a false-positive 'Doctoral Student, Hearing and Speech Department, University of Kansas Medical Center tProfessor and Chairman, Hearing and Speech Department, Associate Dean, School of Allied Health, University of Kansas Medical Center Reprint requests : Stephan McCall, Hearing and Speech Department, University of Kansas Medical Center, 39th and Rainbow Blvd ., Kansas City, KS 66103 18 finding in an ABR screening test (Weber, 1983 ; Levette, 1984 ; Jacobson, 1985) . Certainly one of the more important factors in the successful completion of an examination, however, is the degree of "cooperation" provided by the patient . In the case of infant screening, the highest or ultimate degree is generally achieved when the child is asleep . Several investigations (e .g ., Amadeo and Shagass,1973 ; Goff et a1,1977 ; Sohmer et a1,1978 ; Sanders et al, 1979) have indicated that the ABR parameters show no significant differences in awake versus asleep adults and that one is justified in using this procedure in either state . Although activity state may not affect the brainstem response per se, it certainly influences the amount of myogenic and/or movement artifact present during the test, and this is well recognized . By definition, myogenic artifact is due to muscle action potentials, whereas movement artifact is induced by movement of the head, trunk, and extremities, which weakens or disrupts the electrode contacts (Jacobson, 1985) . Although the ABR is highly repeatable and easily recognized in high quality recording situations, it can be very illusive if tracings are contaminated with myogenic and/or movement artifact due to a fussy or restless patient (Weber, 1983 p . 179) . This, in turn, Pediatric ABR Screening/McCall and Ferraro generally necessitates the administration of sedation when measuring the ABR in infants and toddlers . In newborns, however, sedation is generally not given for a screening examination because of the inherent risks this poses, and also because the activity state of the neonate is usually subdued in comparison to an older child . However, the degree to which movement/myogenic activity can confound the tracings taken from a comparatively quiet neonate may be underestimated . If this is the case, the likelihood of a child failing an ABR screening examination may be greater if the exam is performed when the child is awake versus when he/she is asleep . The present study examined this hypothesis in a clinical setting . METHOD ifty-two medically stable neonates (30 males, F 22 females) served as subjects . The babies were outpatients referred from the University of Kansas Medical Center Neonatal Intensive Care Unit who were considered to be at risk for hearing loss in accordance with the specific risk factors advocated by the Joint Committee on Infant Screening (1982) . The mean postgestational age at the time of testing was 47 .8 weeks (range 37-65) . Testing was done in an examining room where ambient noise levels were within those recommended for neonatal auditory screening (Richmond et al, 1986). ABRs were recorded with a Nicolet "Audit V" evoked potential system . Stimuli were broad band clicks (100 psec electrical pulses) delivered directly to the ear canal using a modified impedance tip adapter coupled to a miniature transducer standard to the Audit V system . Clicks were presented in alternating polarity at a repetition rate of 33 .3 per second . Electroeneephalographic responses were recorded as the potential difference between the forehead and ipsilateral earlobe, with ground at the contralateral earlobe . Voltages were band pass filtered with frequency cutoffs of 100 and 3000 Hz (12 dB per octave) . One thousand five hundred and thirty-four sweeps were electronically averaged to provide a representation of the first 15 msec of electrophysiologic activity (filtered EEG) following stimulus onset . The signal averager incorporated an "artifact rejection" system that automatically discarded trials with amplitudes (peak to peak voltages) exceeding 90 percent full scale deflection . The subject's state of activity during the exam was monitored and recorded in three categories . These included "awake-active" (sucking behavior and mild movement of the extremities), "awakecalm" (very quiet, relatively motionless), and "asleep ." Classification into a particular activity state was based on the consensus of the examiner, a graduate student assistant experienced in pediatric ABR evaluations and the baby's parent/ caregiver . In addition, background electrophysiologic activity was visually monitored for gross differences between asleep and awake states . On occasion, a baby judged to be asleep would begin to move and/or display heightened activity as reflected in the filtered EEG . In these instances, testing would be halted until the EEG stabilized back into the sleeping pattern . Babies classified as asleep had to remain asleep throughout the test to qualify as subjects in this category . Classification as either awake-calm or -active was inherently more subjective . If, for example, a baby initially classified as awake-calm became and stayed active for the majority of runs, classification was changed to awake-active . If a baby's activity changed during the course of the examination and failed to remain stable for the majority of runs, the results were excluded from the study . In addition and regardless of activity state, any trial wherein over 30 percent of the responses were rejected by the computer was excluded . This value was based on experience in our clinic . Accepting responses with higher artifact rejection would most likely lead to higher failure rates . III LATENCY (MS) Figure 1 Normal ABR tracings recorded from an asleep infant . Waves I, III, and V are present at normal absolute and interwave latencies at 60 and 30 dB HL . Journal of the American Academy of Audiology/Volume 2, Number 1, January 1991 Screening protocol called for measurements at Hearing Levels of 60 dB and 30 dB per ear with one replication at each level . Figure 1 shows an example of a normal response recorded from a subject who was asleep when tested. The baby was considered to have passed the screening if a repeatable wave V was observed at normal and symmetrical latency values at 30 dB HL in both ears (based on age-dependent laboratory norms) . Final judgments of pass or fail were determined from hard copy recordings of the tracings by an examiner who was unaware of the subject's activity state . Table 1 Summary of Referral Criteria and Pass/Fail Results for All Subjects Category Craniofacial abnormality Family history Referred Fail Pass 2 0 0 0 2 0 2 1 Low birthweight 22 8 14 Ototoxic medication 14 4 10 Hyperbillrubinemia Viral infection Breathing difficulty Multiple Total 0 3 9 52 1 0 0 0 3 6 3 19 (37%) 33 (63%) RESULTS esults were obtained from 30 male and 22 R female neonates . Table 1 summarizes referral criteria and the pass-fail results of all subjects . The activity state of each baby was recorded as either "awake-active," "awake-calm," or "asleep ." Eleven additional babies (17%) were excluded because activity state fluctuated during the ABR examination and exclusive placement into one of the three defined categories was not possible . Examples of tracings recorded in each of the three activity states are illustrated in Figures 2 and 3 . A visual comparison indicates the possible effects of increased myogenic/movement artifact on the clarity of the ABR tracing. Figure 2 shows recordings taken from a baby tested while awake and calm and then again when asleep . The "awake-calm" recording produced observable components at both intensity levels but morphology was poorly defined . However, when the same baby was tested when asleep, the waveforms became well defined and repeatable . The disparity between awake versus asleep states was even more A B LATENCY (MS) 20 apparent when recordings were taken in the "awake-active" state as shown in Figure 3 . Identifiable components were observed at 60 dB HL, but at 30 dB HL the waveform was distorted and the components were difficult to define resulting in an evaluation of "Fail ." When this same baby was tested in the "asleep" state (Fig . 3), recordings were well defined and normal (Pass) . Of the 52 neonates included in this study, 28 were screened while asleep . Twenty-five passed and 3 failed . Twenty-four babies were screened in the awake state . Eight passed and 16 failed . Table 2 indicates Chi-Square analysis for awake-asleep and pass-fail conditions . Results of these data indicated a significant difference (p < 0 .05) in passfail rates between babies who were screened in awake versus asleep states . This suggests that an awake baby will be more likely to fail an ABR screening than one who is asleep . In the awake state, babies were classified as either "awake-active" or "awake-calm ." This was done to determine if seemingly subtle changes in Figure 2 ABR tracings recorded from the same infant first in the "awakecalm" state (A) and then in the "asleep" state (B). Comparison shows the asleep tracings to be more clearly defined and repeatable . Pediatric ABR Screening/McCall and Ferraro A Figure 3 ABR tracings recorded from the same infant first in the "awake-active" state (A) and then in the "asleep" state (B). Comparison shows the asleep tracings to be more clearly defined and repeatable (Pass) . Interpretation of the awake-active tracings resulted in an evaluation of "Fail." B 1 .5 L5 LATENCY (ms) activity state could vary enough in awake neonates to significantly affect interpretation and consequently determination of pass-fail . Of the 24 awake babies, 14 were screened in the "awake-active" state, 4 passed and 10 failed . Ten babies were screened in the "awake-calm" state, four passed and six failed . Table 3 indicates chi-square analysis for awake-active, awake-calm, and pass-fail conditions . Results of these data revealed no significant differences in pass-fail rate between awake-active and awake-calm babies (p > 0 .05) . This study was primarily concerned with neonates assessed in a clinical setting using conventional ABR screening procedures . Ideally, we would have preferred to test each baby in all three activity states . However, we were not at liberty to administer sedation at will because of the inherent risk factors associated with doing this, nor would it have been realistic to maintain all three activity states for a full recording session or during three separate sessions . Currently, we are in the process of collecting long-term follow-up data on each of these subjects . However, during the course of the study, a certain number of babies who were initially screened while awake and failed were seen again . Of the 16 awake-fails, eight were seen again 4 to 8 weeks later . Six were tested when asleep, five passed and only one failed . The other two were awake for the second screening and both again failed . This information suggests that five of six babies who were initially screened while awake might have been false-positives . Since a time period of 4 to 8 weeks elapsed between initial and follow-up screenings, the possibilities of fluctuating or resolved hearing loss and/or maturational effects are very real . Although six subjects represent a small sample size, the number of possible false-positives is large, again suggesting that Table 2 Chi-Square Analysis for Awake versus Asleep Pass/Fail Conditions Table 3 Chi-Square Analysis for Awake-Calm versus Awake-Active Pass/Fail Conditions ASLEEP PASS FAIL 25 AWAKE 8 17 .8 3 28 33 152 16 10,2 X2=172 AWAKE I I 8.8 24 19 52 p<005 CALM PASS FAIL 10 4 3 .3 i 6 .7 10 ACTIVE 4 .7 8 X2 = .45 14 9 .3 16 'I p > 0 .05 24 Journal of the American Academy of Audiology/Volume 2, Number 1, January 1991 myogenic/movement artifact from an awake baby may have contributed to poor definition of the ABR waveform . DISCUSSION AND CONCLUSIONS ased on the results of several studies, failure B rates in pediatric ABR screening programs generally range from 10 percent to 25 percent (Fria, 1985) . Some reports have indicated failure rates as low as 5 percent (Schulman-Galambos and Galambos, 1979), whereas others observed failure rates near 60 percent (Roberts et al, 1982) . Differences in testing apparati and protocol as well as pass/fail criteria certainly contributed to this disparate range . However, one aspect that is certainly well recognized but generally not reported is the effect(s) of subject activity state on the outcome of an examination . In the present study, the initial overall failure rate of the 52 neonates tested was approximately 37 percent (19/52), which is on the "high" side . Failure rate for those subjects tested awake was approximately 67 percent (16/24), which is extremely high . On the other hand, the failure rate for those babies tested when asleep was approximately 10 percent (3/28), which is low . The use of a 30 dB HL cut-off may have contributed to our high failure rate for awake babies . We chose this level to strengthen test sensitivity . Those studies utilizing a 40-dB criterion generally report lower failure rates . This has prompted us to conduct a comparative study regarding this issue, which is currently ongoing. In addition, certain features inherent to the Audit V's artifact rejection system may have contributed to poor waveform morphology in the active infants . Despite the above caveats, our findings suggest that increased muscle or movement activity of an awake neonate may contaminate the ABR enough to lead to a false-positive result in a screening examination . The effects of even subtle activity in a seemingly calm but awake baby should not be underestimated . In several cases, ABRs from babies who were screened in an awake but quiet state were as difficult to interpret as those recorded from a more active baby . On occasion, these same babies fell asleep and the once difficult to interpret waveforms became well defined and easily recognized . The above findings are certainly not surprising and, in many respects, the results of this study simply reaffirm something that is widely recognized . What is surprising, however, is that the ac- 22 tivity state of the neonate is rarely reported or acknowledged in the literature to be a cause for falsepositive findings in screening examinations . Ideally, the baby should be screened while in natural sleep ; however, this is not always practical or feasible . If a baby is awake and fails the screening, steps should be taken to facilitate sleep when the retest is performed and time allowed for this . These efforts may include instructing the parents to keep the baby awake for several hours prior to the exam, feeding the baby immediately before the exam and/or the administration of sedation . Acknowledgment . The authors would like to thank Judith E. Widen, Ph .D ., for her guidance and assistance in the preparation of this manuscript . 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