Prolongation of total permissible circulatory arrest duration by deep hypothermic intermittent circulatory arrest

Objective: We determined whether the duration of permissible circulatory arrest could be prolonged by deep hypothermic intermittent circulatory arrest. Methods: Twenty-five beagles were cooled on bypass to 18 degrees C to initiate deep hypothermia that was maintained for 3 hours. Five protocols were then studied: group 1, uninterrupted bypass during hypothermia; group 2, arrest for 40 minutes during hypothermia; group 3, arrest for 60 minutes during hypothermia; group 4, arrest for 80 minutes during hypothermia; and group 5, intermittent circulatory arrest, consisting of six cycles of 20 minutes of arrest followed by 10 minutes of systemic recirculation during hypothermia (total, 120 minutes of arrest). The oxyhemoglobin concentration in the brain was measured with near infrared spectrophotometry, Results: In groups 2, 3, and 4, the oxyhemoglobin concentration in the brain decreased continuously after arrest, finally reaching a plateau after 24.9 +/- 1.2 minutes. This finding suggested that the available cerebral oxyhemoglobin was depleted. In contrast, the available cerebral oxyhemoglobin was not depleted during hypothermic intermittent arrest in group 5, The mitochondrial respiratory control index was significantly lower in group 4 than in the other groups (p < 0.05). However, there were no significant differences in the respiratory control index for groups 1, 2, 3, and 5, Moreover, the formation of brain edema was significantly lower in group 5 than in the other groups (p < 0.05), Conclusions: These results indicate that deep hypothermic intermittent arrest can increase the duration of total permissible circulatory arrest and will be a useful modality when prolonged arrest is anticipated.