Electroencephalographic observations were performed during hypothermic circulatory arrest at various temperature levels. Changes in cortico- and subcorticograms recorded from 28 ether-anesthetized mongrel dogs were divided into three stages. The termination of arrest within the 1st and the 2nd stages resulted in a complete recovery; whereas that at the 3rd stage resulted in no recovery. This criterion was satisfactorily applied to 20 patients operated on cardiotomy under hypothermic circulatory arrest. Though EEG(scalp) was used, a characteristic pattern appearing exclusively at the beginning period of the 1st and the 2nd stages led to a precise estimation of the length of the 2nd stage proportionally to the length of the 1st stage from the experimental experiences. The safety time limit of circulatory arrest, by the end of the 2nd stage, was 25 to 30 minutes at body temperature of 28°C.
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Fukukei et al. (1966) studied this question.