Effect of bilirubin on brainstem auditory evoked potentials in the asphyxiated rat.

We measured brainstem auditory evoked responses (BAER) in four groups of paralyzed, ventilated, adult rats. Group A (n = 2) received intravenous albumin; group B (n = 5) received bilirubin in albumin; group C (n = 7) was asphyxiated and then received albumin; and group D (n = 19) was asphyxiated and received bilirubin in albumin. When compared with control values, no changes in BAER occurred in groups A or B and only slight changes were found in group C. In group D, seven rats died and seven suffered a marked secondary deterioration of the BAER following recovery, a phenomenon that did not occur in group C (p = 0.02). Bilirubin toxicity appears to be responsible for the changes in BAER but prior asphyxia was necessary for this effect to occur. Because the changes that occurred in group D involved all four major waves, it is not possible to separate out a toxic effect of bilirubin, localized to the auditory nerve and the auditory pathway, from a generalized systemic effect which could cause attenuation of the entire response. The BAER may be useful, however, as a noninvasive means of identifying bilirubin toxicity in the newborn.