Changes in brainstem auditory evoked response latency predict survival after CPR in a rat model of cardiac arrest and...

Brainstem auditory evoked responses (BAER) are routinely used to monitor brainstem function in hospitalized comatose patients. We used a rat model of cardiac arrest and resuscitation to explore the possibility that the BAER, monitored during and immediately after cardiopulmonary resuscitation (CPR), could be used to determine whether the CPR was effective in restoring brainstem blood flow. Long-Evans rats were subjected to 7 min of cardiac arrest, induced by chest compression under Ketamine anesthesia sufficient to mechanically prevent the heart from pumping blood and were then resuscitated using a standard CPR protocol. During CPR, click stimuli were applied to one ear at 11/s and BAER averages recorded every 15 s. In three rats the BAER did not return after CPR; none of these rats respired spontaneously and all died. In 33 rats the BAER did return; within 15 min after the start of CPR BAER peak latencies decreased rapidly, increased again and then decreased. If the increase in the latency of the N2 peak was less than 0.3 ms, then the rat survived. If it was greater than 0.35 ms the rat died. This signal was used as a cue for intervention in three rats; two survived. Thus, in this preparation, the BAER provided a useful measure of CPR effectiveness, in time to permit successful intervention.