EEG and prognosis of neurologic recovery of dogs under profound hypothermic circulatory arrest

Deep hypothermia (18-20°C) (DH) during prolonged circulatory arrest and cardiopulmonary bypass is used to repair complex intracardiac lesions and vascular neurosurgical lesions. DH diminishes the risk of ischemic damage and multiorgan failure after circulatory arrest. Profound hypothermia (PH) to 6-7°C has recently been reported to improve the neurological outcome of dogs after 2 h of circulatory arrest. There are no reports of the possible utility of EEG activity to predict the neurological outcome. As a part of a controlled study of cardiopulmonary bypass and 2 h of circulatory arrest we compared EEG recovery to the neurological outcome in 2 groups of dogs: 4 under DH and 4 under PH. All of the dogs under PH had a good outcome: mean neurodeficit score was 6.25 500 in PH and 139.25 500 in DH dogs (P < 0.03); mean histopathological score was 19.25 100 for DH and 47.75 100 in PH dogs (P < 0.03). EEG activity 2 h after reperfusion and starting of rewarming correlated with eventual neurological outcome. EEG variables associated with good outcome were: main final frequency and degree of rhythmicity of the activity. We conclude that PH exerted a protective effect for animals undergoing 2 h of circulatory arrest. EEG was a useful tool for predicting neurological outcome under the studied conditions.