Auditory brainstem evoked responses and temperature monitoring during pediatric cardiopulmonary bypass

Purpose: To examine the effects of temperature on auditory brainstem respon ses (ABRs) in infants during hypothermic cardiopulmonary bypass for total c irculatory arrest (TCA). The relationship between ABRs (as a surrogate meas ure of core-brain temperature) and body temperature as measured at several temperature monitoring sites was determined. Methods: In a prospective, observational study ABRs were recorded non-invas ively at normothermia and at every 1 or 2 degrees C change in ear-canal tem perature during cooling and rewarming in 15 infants (ages: 2 days to 14 mon ths) that required TCA. The ABR latencies and amplitudes and the lowest tem peratures at which an ABR was identified (the threshold) were measured duri ng both cooling and rewarming, Temperatures from four standard temperature monitoring sites were simultaneously recorded. Results: The latencies of ABRs increased and amplitudes decreased with cool ing (P < 0.01), but rewarming reversed these effects. The ABR threshold tem perature as related to each monitoring site tear-canal, nasopharynx, esopha gus and bladder was respectively determined as 23 +/- 2.2 degrees C, 20.8 /- 1.7 degrees C, 14.6 +/- 3.4 degrees C, and 21.5 +/- 3.8 degrees C during cooling and 21.8 +/- 1.6 degrees C, 22.4 +/- 2.0 degrees C, 27.6 +/- 3.6 d egrees C, and 23.0 +/- 2.4 degrees C during rewarming, The rewarming latenc ies were shorter and Q(10) latencies smaller than the corresponding cooling values (P < 0.01). Esophageal and bladder sites were more susceptible to t emperature variations as compared with the ear-canal and nasopharynx. Conclusion: No temperature site reliably predicted an electrophysiological threshold. A faster latency recovery during rewarming suggests that body te mperature monitoring underestimates the effects of rewarming in the core-br ain. ABRs may be helpful to monitor the effects of cooling and rewarming on the core-brain during pediatric cardiopulmonary bypass.