Sivelestat Treatment for Postoperative Organ Protection in Type A Aortic Dissection

The goal of this multicenter, double-blind, randomized controlled trial is to learn if sivelestat sodium (Siv) can protect the organ function in patients suffered operation for acute type A aortic dissection. The main questions it aims to answer are: * Can the 3-day-treatment of Siv enlarge the Day-0-to-Day-5 drop in the organ-health score (SOFA score)? * Can this treatment significantly shrink the area under the SOFA curve from first dose to Day 5? * Can this treatment significantly improve the end of patients in 28 days (clinical outcomes)? Researchers will compare drug Siv to a placebo (a look-alike substance that contains no drug) to see if drug Siv works. Participants will: * Take drug Siv or the placebo through vein continuously for 72 hours * Receiving regular intensive care in ICU after the operation

Inclusion Criteria: 1. Age 18-75 years inclusive. 2. Written informed consent obtained before participation. 3. Confirmed acute Stanford type A aortic dissection scheduled for surgical repair. Exclusion Criteria: 1. Life expectancy ≤ 48 hours. 2. Pregnant or lactation. 3. Severe pre-operative liver dysfunction: Child-Turcotte-Pugh score 10-15. 4. Severe pre-operative renal dysfunction: acute or chronic kidney injury meeting criteria for renal-replacement therapy. 5. Confirmed COPD or asthma. 6. Immunosuppression: long-term or \> 2 weeks continuous systemic corticosteroids. 7. Concomitant or anticipated use of immunomodulators (Xue-Bi-Jing injection, thymosin, IVIG). 8. Medical or psychological condition that would interfere with study participation, assessment, or outcomes.