Effects of hypoxic-ischemic encephalopathy and whole-body hypothermia on neonatal auditory function: a pilot study

Abstract

We assessed the effects of hypoxic-ischemic encephalopathy (HIE) and whole-body hypothermia therapy on auditory brain stem evoked responses (ABRs) and distortion product otoacoustic emissions (DPOAEs). We performed serial assessments of ABRs and DPOAEs in newborns with moderate or severe HIE, randomized to hypothermia ( N = 4) or usual care ( N = 5). Participants were five boys and four girls with mean gestational age (standard deviation) of 38.9 (1.8) weeks. During the first week of life, peripheral auditory function, as measured by the DPOAEs, was disrupted in all nine subjects. ABRs were delayed but central transmission was intact, suggesting a peripheral rather than a central neural insult. By 3 weeks of age, peripheral auditory function normalized. Hypothermia temporarily prolonged the ABR, more so for waves generated higher in the brain stem but the effects reversed quickly on rewarming. Neonatal audiometric testing is feasible, noninvasive, and capable of enhancing our understanding of the effects of HIE and hypothermia on auditory function.

Figure 1

Distortion product otoacoustic emission (DPOAE) waveforms in three study newborns (cases 4, 6, and 8) tested within the first week and repeated more than 3 weeks after birth. Despite failing to produce DPOAEs shortly after birth, all three study newborns tested after 3 weeks had reliable DPOAEs. All cases demonstrated high amplitudes at the lowest and highest frequency ranges. The emissions in the midrange of the assessed frequencies for cases 6 and 8 were of relatively low amplitude.

Figure 2

Serial brain stem evoked response (ABR) recordings from a subject (case 6) during and following hypothermia therapy. The dashed vertical lines indicate the latencies of the three prominent waves (I, III, and V) from the first recording 2 hours after the onset of hypothermia therapy. Following 26 hours of hypothermia, the latencies increased slightly. Immediately following complete rewarming, there was a reduction in waves III and V latencies as compared with the first recording. The ABR latencies 3 weeks later suggest a further decrement in wave III and V latencies with little additional change in wave I latency.