Objectives: Prolonged mechanical ventilation (PMV) after surgical repair of acute type-A aortic dissection (ATAAD) is associated with an increased risk for mortality and morbidity. The goal of this study was to evaluate the influence of PMV on early and late outcomes and to identify the risk factors for PMV after ATAAD repair. Design, Setting, and Participants: This study was a retrospective analysis of prospectively collected data, which resulted from a prior clinical trial. Clinical outcomes were analyzed in 121 patients with ATAAD (mean age 46.6 +/- 10.4; 93 men) who underwent total arch replacement combined with a frozen elephant trunk implantation at a mean of 3.6 days from onset. Multivariate analysis was used to identify risk factors for PMV after surgery. Measurements and Main Results: The primary endpoint of this study was the occurrence of PMV after ATAAD surgery. The secondary endpoints were risk factors for PMV, in-hospital mortality, and 1-year survival. Thirty-five (28.9%) patients required PMV. The PMV group demonstrated a longer ventilation time and length of intensive care unit stay (129 +/- 79 h and 167 +/- 119 h v 19 +/- 10 h and 32 +/- 23 h, respectively, p < 0.001). Postoperative mortality was 6.6% (8 of 121), including 6 (17.2%) in the PMV and 2 (2.3%) in the non-PMV groups (p = 0.003). PMV was associated with increased in-hospital mortality (odds ratio 6.4; 95% confidence interval 1.1-36.0; p = 0.036). Follow-up was complete in 88.6% (98 of 113) of patients at a mean of 26 months (1-39 mo). Survival at 1 year was significantly lower in the PMV group compared with the non-PMV group (77.1% v 95.3%, p = 0.002). Risk factors for PMV were the level of serum lactate (mmol/L) at the end of surgery (odds ratio 1.189; 95% confidence interval 1.026-1.377; p = 0.021) and a lower preoperative platelet count (10(9)/L) (odds ratio 0.918; 95% confidence interval 0.847-0.994; p = 0.034). Conclusion: In this study, the occurrence of PMV was 28.9% in patients with ATAAD. A lower preoperative platelet count and a higher serum lactate level after ATAAD surgery were risk factors for PMV. Identification of risk factors may be helpful for preventing PMV and improving outcomes after surgical repair of ATAAD. (C) 2017 Elsevier Inc. All rights reserved.