[Reference range of the auditory brainstem response for the patients in the NICU]

Since the auditory brainstem response (ABR) test is a test for the brainstem capacity and hearing function, it is recorded at the discharge from the neonatal intensive care unit (NICU) in our hospital. Although the reference range for the normal full-term newborn infants is well documented, that for the pre-term newborn and/or low birth weight infants is yet to be determined. The latency between wave-I peak and wave-V peak (I-V inter peak latency) on the ABR test was measured on the 254 infants (124 males and 130 females) of 36 to 45 corrected weeks old which was defined as the sum of the gestational weeks and weeks after birth at the test. The reference range for each corrected age group is set as mean +/- standard deviation. The mean value tends to be short as the corrected age increases, while it is not affected by the gestational weeks, body weight on birth, blood bilirubin level, neonatal asphyxia (defined as Apgar score at 1 minute after birth is less than 5), or intrauterine growth retardation. Eight out of 254 patients showed the abnormal values; among the 8 patients, 3 had brain diseases (intraventricular hemorrhage, intracranial hemorrhage, and microcephaly) and 1 with Down's syndrome. Thus the brain stem function testing at a discharge from NICU is important for the neurophysiological prognosis of the patients and the ABR test with the reference range defined here can be a useful tool.