Brain-stem auditory evoked responses to hypercarbia in preterm infants

To determine the effect of acute hypercarbia on brain-stem function in preterm neonates, we compared brain-stem auditory evoked responses (BAERs) during 8% CO₂ breathing to those elicited during room air breathing in 12 healthy preterm infants during the first week of life. End-tidal CO₂ (ETpCO₂), respiratory rate and depth were monitored throughout the protocol. Absolute wave latencies and interpeak intervals of the BAERs were ana;yzed from duplicate trials. During 8% CO₂ breathing, ETpCO₂, respiratory rate depth of respiration increased significantly (p < 0.05). The absolute latency of wave V was prolonged (P < 0.025). Values of absolute peak latencies I and III were unaffected by the hypercarbic state. These data demonstrate that elevations in pCO₂ which elicit ventilatory responses also effect the BAER. The specific effects on ventilatory pattern, peak V latency and interpeak interval III-V indicate brain-stem responsiveness and alterations in the more central components of the auditory pathway. These findings raise important considerations regarding the influence of hypercarbia on brain-stem function preterm infants and the clinical management of such infants with abnormalities of gas exchange.