Mediation effect on cardiopulmonary bypass time between intraoperative ultrafiltration volume and 90 d postoperative mortality in patients with Stanford type A aortic dissection
Objective To explore the mediation effect on cardiopulmonary bypass(CPB)time(TCPB)between intraoperative ultrafiltration volume(UFV)and 90 d postoperative mortality in patients with Stanford type A aortic dissection(TAAD).Methods Retrospective analysis of clinical data of 176 patients with TAAD admitted to the Department of Cardiovascular Surgery,Nanfang Hospital.Southern Medical University from January 2018 to July 2022 who underwent surgery,and they were divided into the survival group(157 patients)and the death group(19 patients)based on 90 d postoperative survival.Baseline and perioperative clinical indicators were compared between the two groups.Mediation analyses were performed to analyse the mediation effect on TCPB between UFV and the outcome event(occurrence of death at 90 d postoperatively)using Mplus 8.0 software.As the ending event variables were dichotomous,the mediation analysis effect sizes were isoscaled using stdyx complete standardisation and tested using the bootstrap method corrected for non-parametric percentile bias with repeated self-sampling 10 000 times.Results The mortality rate within 90 d in the whole group of patients in this study was 10.79％.Comparison of TCPB,aortic block time,total fluid intake and total output in CPB,total ultrafiltration volume,UFV,postoperative ventilator time,awake time,incidence of cerebral complications,use of continuous renal replacement therapy(CRRT)and application of extracorporeal membrane pulmonary oxygenation,incidence of adverse events of wound healing,and postoperative hospital day metrics between the two groups,the differences were statistically significant(P＜0.05).The results of mediation analysis showed that TCPB played a partial mediating role(total effect,direct effect,and intermediate effect were all significant)between UFV and outcome events after standardization.The total effect was 0.334(95％CI:0.098-0.544,P=0.003),and the direct effect size was 0.225(95％CI:0.005-0.444,P=0.043),and the mediation effect was 0.109(95％CI:0.024-0.216.P=0.024).Conclusion TCPB plays a partial mediating role between UFV and the occurrence of death within 90 d postoperatively in patients with TAAD,and shortening TCPB should be prioritised over reducing UFV in order to improve the prognosis of patients with TAAD.Parameter estimation in small-sample simple mediation models with dichotomous dependent variables uses robust weighted least square mean and variance adjusted weighted least squares combined with the stdyx method affects the mediation effect results.
Ultrafiltration volumeCardiopulmonary bypass timeMortalityMediating effectStanford type A aortic dissectionCategorical variableDichotomous dependent variableCausal inference
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