Electrocochleogram and Auditory Brainstem Response During Hypothermia

Abstract

The effect of hypothermic condition upon ECochG and ABR was examined in 10 children with congenital heart anomalies. The age of children was ranged 11 months to 9 years old, and they underwent open heart surgeries under hypothermic anesthesia. The entire body was cooled to about 21°C over a period of 1 hour by the surface cooling method. After completion of their open heart surgeries, the patients were rewarmed to normothermia. The responses to click of 115dB SPL were recorded one day before the surgery and during the period of cooling and rewarming. As the temperature was going down, the latencies of N₁ (wave I), wave III and V were linearly increased, and the increase rates in average were 0.11, 0.25 and 0.43msec/°C in wave I. II and V, respectively. The wave III and V were no longer present around 24°C but N₁ disappeared at the lower temperature by 1 to 2°C. The SP was the most resistant to hypothermic condition and was recorded throughout the observation. The most interesting phenomenon in this study was the temporary increase in N₁ amplitude which reached the peak value at 30°C and was reduced thereafter. At the time of rewarming, SP reappeared first and was followed by N₁, and finally the wave III and V reappeared. The results obtained in the present study indicate that the brainstem in the most sensitive to hypothermia, followed by the cochlear nerve and the sensory hair cells are the most resistant to hypothermic condition.