Auditory brainstem response in neonates with hypoxic-ischemic-encephalopathy following perinatal asphyxia

The technique of auditory brainstem evoked responses testing (ABR) was applied to twenty four new born infants with asphyxia complicated by hypoxic-ischemic-encephalopathy (HIE) in an attempt to study potential influence of HIE on hearing impairment. Twenty normal term neonates with no apparent neurological disorder, were also examined for comparison. Twenty two per cent (n = 5) of the patients with HIE showed some abnormality in the ABR pattern, the major one being a transient elevation in threshold of wave V (n = 4; 16.6%). ABR abnormalities, however, were found with greater frequency in neonates with Stage II HIE (75% vs 10%, p less than 0.001). Further ABR abnormalities were found in Stage II HIE only when duration of neurological abnormalities was greater than 5 days. There was no difference, however, between the ABR latencies of the asphyxiated and non-asphyxiated newborn infants (p greater than 0.05). One neonate (4%) with severe HIE, however, had persistent ABR abnormality in the form of bilateral absence of all waves in the later part of the ABR with preservation of wave I. This implied only cochlear functions and absence of any brainstem conduction. These results indicate that birth asphyxia complicated by HIE is a significant high risk factor for hearing impairment in the affected neonates. This justifies ABR testing of neonates with HIE (particularly Stage III), at the time of their discharge, as a screening procedure for early detection of permanent hearing loss.