OBJECTIVES: The relationship between cooling status during aortic surgery with hypothermic circulatory arrest and postoperative neurologic dysfunction remains unknown. In the present study, we evaluated the effect of cooling status on transient neurologic dysfunction after total arch replacement. METHODS: We studied patients who underwent elective total arch replacement with hypothermic circulatory arrest and antegrade selective cerebral perfusion from December 2011 to January 2021. Changes in tympanic temperature trends recorded during surgery were plotted. Several parameters, including the nadir temperature, cooling speed, and degree of cooling (cooling area, or the area under the curve of inverted temperature trends from cooling to rewarming as calculated by the integral method), were analyzed. The relationships between these variables and transient neurologic dysfunction were evaluated. RESULTS: Transient neurologic dysfunction was observed in 33 (14.5%) of the 228 included patients. In the transient neurologic dysfunction group, the cooling area was larger (2417.3 vs. 1920.8 °C min
P <
0.001) and the cooling speed was higher (0.68 vs. 0.51 °C/min
P <
0.001) than in the non-transient neurologic dysfunction group. A multivariate logistic model revealed that both the cooling area (odds ratio = 1.13 per 100 °C min
P <
0.001) and cooling speed (odds ratio = 3.69 per °C/min
P = 0.041) were independent risk factors for transient neurologic dysfunction. CONCLUSIONS: Both the cooling area, which indicates the degree of cooling, and cooling speed had significant relationships with transient neurologic dysfunction after total arch replacement. Together, these findings indicate that overcooling and rapid cooling may contribute to brain injury.