PERINATAL ASPHYXIA, HYPOXIA, ISCHEMIA AND HEARING-LOSS - AN OVERVIEW

Birth hypoxia, asphyxia and ischemia have often been thought to be maj or causes of early hearing loss or deafness. The purpose of the presen t review is to focus on the role of these particular factors for perin atal auditory disorders. On the whole, only a small proportion of neon atal hearing loss is caused by perinatal factors. The exact etiology o f neonatal hearing loss in children with complicated deliveries is dif ficult to evaluate due to the large number of causative factors that m ight be involved. After reviewing the literature covering the past 15- 20 years, it is not possible to say that we understand the relative im portance of different factors and their interactions. However, in the majority of studies, birth asphyxia is not correlated with hearing los s in babies with complicated deliveries. Prolonged artificial ventilat ion, the presence of severe hypoxic ischemic encephalopathy or persist ent pulmonary hypertension are important factors. The brain is more su sceptible to anoxia than the ear and both are more likely to be damage d after prolonged pre-, peri- and postnatal hypoxia-ischemia than pure hypoxia during delivery. Perinatal hypoxia is more likely to cause a temporary hearing loss than a permanent one. Preterm babies are more v ulnerable than term babies. The total number of risk factors, e.g. ind icated by total length of stay in the neonatal intensive care unit and length of artificial ventilation, is the best predictor of risk for h earing loss of perinatal origin. The similarities between hearing loss and cerebral palsy are pointed out; only 8% of the cases of cerebral palsy are considered to be caused by conditions during delivery.