Choreoathetosis after deep hypothermia without circulatory arrest In 8 of 758 patients undergoing an intracardiac operation under cardiopulmonary bypass and hypothermia, choreoathetosis developed 3 to 7 days postoperatively. Before the onset of choreoathetosis, varying degrees of neurological dysfunction were noted. Electroencephalography and neuroimaging failed to detect any responsible functional or structural changes. Six patients are alive 1 to 3 years postoperatively, and their condition is improving. Two patients died of aspiration or sepsis. All patients were grouped based on factors identified as being possibly causative: depth of hypothermia, cooling time, flow rate, and repeated hypothermia. The incidence of choreoathetosis was significantly different in group A (rectal temperature greater than 25 degrees C) compared with group B (rectal temperature less than or equal to 25 degrees C) (0/295 versus 8/463; p = 0.02). Based on cooling time, the incidence of choreoathetosis was significantly different in group B1 (cooling time less than 1 hour) compared with group B2 (cooling time greater than or equal to 1 hour) (1/220 versus 7/243; p = 0.05). Based on flow rate during cooling, group B2 was further divided into the low-flow group (less than 1,500 mL.min-1.m-2) and the high-flow group (greater than or equal to 1,500 mL.min-1.m-2). Although not significant, the incidence of choreoathetosis was higher in the high-flow group (6/153 versus 1/90; p = 0.22). In group B patients having reoperation, the incidence of choreoathetosis was higher than in patients operated on for the first time (5/54 versus 3/409; p less than or equal to 0.0001). 