Maximum Length Sequence Brainstem Auditory Evoked Responses in Term Neonates Who Have Perinatal Hypoxia-Ischemia

Abstract

Maximum length sequence brainstem auditory evoked response (BAER) was studied within the first week after birth in 28 term neonates who had perinatal hypoxia-ischemia, or asphyxia. In the BAER recorded using conventional averaging techniques (click rate 21/s), the only abnormality was a slight increase in III-V interval, in addition to an increase in wave latencies when including those who had an elevated threshold (t test, all p Ͻ 0.05). In the maximum length sequence BAER, however, both the III-V and I-V intervals in the asphyxiated infants were significantly increased at all the 91/s, 227/s, 455/s, and particularly 910/s click rates (p Ͻ 0.05-0.001). The I-III interval was also increased significantly at 455/s and 910/s click rates (both p Ͻ 0.05). Wave V amplitude was significantly reduced at all the click rates used (ANOVA, p Ͻ 0.05-0.001), particularly at 910/s, which sometimes was the only abnormality indicative of brain damage. Both the amplitude ratios V/I and V/III were significantly decreased at 455/s and 910/s click rates (p Ͻ 0.01 or 0.001). A general trend was that BAER abnormalities after hypoxia-ischemia became more prominent as click rate was increased. Significant abnormalities occurred mainly at very high click rates (455/s and 910/s), which can be achieved using the maximum length sequence technique but not by using conventional averaging techniques. Thus, this technique, which can be used at the cribside, appears to be a better method for the early detection of brain damage after hypoxia-ischemia than using conventional averaging techniques, enhancing the diagnostic value of the BAER. Abbreviations BAER, brainstem auditory evoked response nHL, normal hearing level HI, hypoxia-ischemia MLS, maximum length sequence HI, or asphyxia, remains an important cause of perinatally acquired brain damage in term babies with subsequent lifelong sequelae (1). About half of term babies who have major symptoms of HI after asphyxia will die or sustain severe disability (2). Early intervention with neuroprotective and therapeutic measures is important for improving their outcome. This largely relies on early detection of neuropathology after HI. One of the currently available tests is BAER (3-7). Information derived from the BAER can predict cranial ultrasonographic abnormalities in neonates at risk for brain injury (6). However, the BAER has only modest association with neurologic status, and false-negative results are common (7). Babies with neurologic deficits often do not show any apparent abnormalities in the BAER. Thus, for babies with a normal BAER, we cannot rule out the possibility of early or subtle brain damage.The method of increasing stimulus rate while recording the BAER has been suggested by some investigators to be a stimulus challenge test or stress test for detecting certain neuropathology that cannot be demonstrated by the BAER elicited with conventional stimulus rates (usually 11/s or 21/s; (3, 8 -14). Our previous studies of the BAER in babies with various clinical conditions that may aff...

Brainstem Auditory Function at Term in Preterm Babies With and Without Perinatal Complications

“…These MLS BAER abnormalities indicate brainstem auditory impairment and/or developmental delay in the preterm babies with perinatal complications, which becomes more apparent following very stressful stimulation. In addition, the increased rate-dependent change in the III-V interval suggests that the efficacy of synaptic transmission in the central auditory system is impaired (15,16).…”

“…More recently, we have used MLS BAER to study functional integrity and maturation of the brainstem and central auditory system (15,16). The major advantage of this technique is that it can present acoustic stimuli up to 1000/s or even higher.…”

“…This technique can present acoustic stimuli much higher than possible with a conventional averaging technique (13)(14)(15)(16) …”

“…As reported previously (15,16), the acoustic stimuli we used were rarefaction clicks of 100 s, delivered monaurally through a TDH 39 earphone. Before recording MLS BAER, conventional BAER was recorded with clicks at 21/s for comparison and determining BAER threshold.…”

“…60 dB nHL for thresholds Յ20 dB nHL, 70 dB nHL for thresholds Ͼ20 -30 dB nHL, or 80 dB nHL for thresholds Ͼ30 dB nHL (15,16). However, to minimize the effect of peripheral auditory impairment on MLS BAER central components, babies with a significantly elevated BAER threshold (Ͼ35 dB nHL), suggesting peripheral auditory disorders, were excluded.…”