• Masakazu Hayashida, Hiroshi Sekiyama, Ryo Orii, Mieko Chinzei, Makoto Ogawa, Hideko Arita, Kazuo Hanaoka, and Shin-Ichi Takamoto.
• Department of Anesthesiology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan. hayashida-todai@umin.ac.jp
• J. Cardiothorac. Vasc. Anesth. 2007 Feb 1;21(1):61-7.

ObjectiveNo systematic study has been conducted to investigate effects of deep hypothermic circulatory arrest (DHCA) on electroencephalographic bispectral index (BIS) and suppression ratio (SR). Thus, the effects of DHCA were evaluated on BIS and SR.DesignA prospective clinical study.SettingUniversity hospital (single institute).ParticipantsTwenty consecutive patients undergoing thoracic aortic surgery using DHCA under narcotics-sevoflurane anesthesia.InterventionsBIS and SR were monitored during cardiopulmonary bypass, simultaneously with nasopharyngeal temperature (NPT).Measurements And Main ResultsBIS decreased to 0 with induction of deep hypothermia and rose again with rewarming, although rates of BIS changes in response to cooling and rewarming varied widely among patients. Typically, BIS decreased slowly until NPT reached 26 degrees C during cooling and then it began to decrease rapidly and reached 0 at 17 degrees C, in inverse proportion to SR, which increased rapidly with deep hypothermia and reached 100% at 17 degrees C. When SR was 50% or more, BIS was determined by SR according to the expression: BIS = 50-SR/2. With rewarming, BIS rose again and returned to precooling baseline levels. Time to the beginning of the BIS recovery significantly correlated with duration of DHCA.ConclusionsWith induction of deep hypothermia, BIS decreased in a biphasic manner to 0 at rates varying among patients. With rewarming, BIS rose again at rates extremely widely varying among patients. The rate of BIS recovery was related to duration of DHCA. BIS may be capable of conveniently tracing suppression and recovery of a part of cerebral electrical activity before, during, and after DHCA.

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