Effect of hypothermia upon the electrocochleogram and auditory evoked brainstem response

The effects of hypothermia upon electrocochleogram (ECochG) and auditory evoked brainstem response (ABR) were studied in 10 children who underwent the open heart surgery under hypothermic anesthesia. The latencies of N1, waves III and V in response to click of 115 dB p.e. SPL were prolonged at the rate of 0.12 +/- 0.02, 0.25 +/- 0.04 and 0.43 +/- 0.05 msec/degree C, respectively. The N1 amplitude was initially increased, returned to the precooling value at about 26 degrees C and decreased thereafter. SP was increased in amplitude by hypothermia and never disappeared throughout the observation. At the time of rewarming, SP appeared first, followed by N1 and finally by waves III and V. The results obtained in the present study were discussed in the light of the sensitivity of the sensory hair cells, peripheral nerves and CNS to the hypothermic condition.