This study was approved by The Ethics Committee of Second Affiliated Hospital of Zhejiang University (IRB: 2016-049) and written informed consent was obtained from all subjects participating in the trial. Study protocol was presented as supporting information and the trial was registered prior to patient enrollment at clinicaltrials.gov. A double-blind, randomized, and controlled prospective trial was conducted from February 11, 2017 to May 05, 2017. Inclusion criteria were patients undergoing elective valvular cardiac surgery with CPB, an age greater than 18 years and normal preoperative haemoglobin level (hemoglobin > 120 g/dl for men and > 110 g/dl for women). Exclusion criteria were a history of cerebral infarction, the presence of arterial or venous thrombosis, a history of myocardial infarction in the previous 7 days, preoperative chronic kidney disease [CKD] (serum creatinine (Cr) by 1.6 mg/dL for men and > 1.4 mg/dL for women or needing for renal replacement therapy), preoperative chronic liver disease (grade B or C of the Child-Pugh classification), a previous history of endocarditis, anemia(< 120 g/dl for men and < 110 g/dl for women), hyperlipidemia, heart failure, preoperative shock, treatment with preoperative coagulation medication within 5 days of surgery (warfarin, aspirin, antifibrinolytic or thrombolytic treatment), preoperative coagulopathy (international normalized ratio (INR) > 1.5, platelet count < 100 × 103/mm3, fibrinogen < 1 g/L), previous sternotomy, emergency procedures, endocarditis, complex surgeries (combined with coronary artery bypass graft surgery, aortic surgery, carotid surgery, other nonvalvular surgery, experienced deep hypothermic circulatory arrest), allergy or contraindication to tranexamic acid, pregnancy, and participation in another study.
Thirty patients were identified and randomly divided into a placebo group, low-dose TXA group and high-dose TXA group by 1:1:1 using numbered sealed envelopes. Patients, surgical team, and data investigators were unaware of the group assignments. Intra-operative TXA (Conba Bio-Pharm.Co.,Ltd., Jin-hua Zhe-jiang, 0.5 g/100 ml) was injected into the central vein until the wound dressings were placed by the anesthesiologist. The low-dose scheme was adapted from Horrow et al[7]. and the high-dose method was based on the dosing regimenn reported by Dowd et al[8]. In the low-dose TXA group, patients received a loading dose of 10 mg/kg 15 min after intubation, followed by a 1 mg*kg− 1*h− 1 infusion. In the high-dose TXA group, a 30 mg/kg bolus was administered, followed by continuous infusion of 16 mg*kg− 1*h− 1. Additional TXA doses of 1 mg/kg and 2 mg/kg were added to the venous reservoir of the low-dose and high-dose groups, respectively, during CPB. An independent investigator generated the random allocation sequence and informed another independent nurse who prepared the study drug with a 100 ml isotonic solution for bolus administration (TXA concentration: low dose = 0.1 mg*kg− 1*h− 1; high dose = 0.3 mg*kg− 1*h− 1) 10 min before administration of TXA. A 50 ml isotonic solution a was continuously infused at a rate of 5 ml/h during the operation (TXA concentration: low dose = 0.2 mg*kg− 1*h− 1; high dose = 3.2 mg*kg− 1*h− 1) and a 20 ml syringe contained the priming solution in the venous reservoir (TXA concentration: low dose = 0.05 mg*kg− 1*h− 1; high dose = 0.1 mg*kg− 1*h− 1). Other perioperative anesthesia management, blood transfusions strategy and post-operative management strategy was consistent with our previous published study[13].
Blood samples were collected into tubes containing 3.8% sodium citrate from the internal jugular vein at the following sample points: (i) preoperatively before TXA injection (baseline), (ii) 5 min after the administration of the TXA bolus (bolus), (iii) 5 min after the onset of CPB (CPB), (iv) 5 min before the end of CPB (end of CPB) and (v) 5 min after the protamine injection (protamine). The tube was immediately placed in a 4 °C refrigerator, centrifuged for 20 min at 3000 rpm at 4 °C within 1 h, and then stored at -80 °C until further testing.
Primary outcome
Intraoperative plasma levels of the following coagulation proteins were measured: plasminogen activator inhibitor-1 (PAI-1), thrombin activatable fibrinolysis inhibitor (TAFI),plasmin-antiplasmin complex (PAP), tissue plasminogen activator (tPA), and thrombomodulin (TM). An independent investigator assayed the plasma concentrations of those coagulation proteins with enzyme immunoassays according to the manufacturer’s instructions (ELISA; Shanghai Jianglai Biotech, Shanghai, China). The details of those coagulation proteins are presented in supplemental Table 1. The changes in the concentrations of coagulation proteins caused by hemodilution were corrected using the following formula: corrected concentration = (sample blood concentration × baseline blood hematocrit)/sample blood hematocrit [14].
Secondary outcome: Intra-operative standard coagulation test and TEG tests were performed. Postoperative laboratory data was collected when arriving at ICU and in the first post-operative morning. Demographic and surgical data was also collected.
Statistical Methods
Given that there are no published studies to guide a power calculation, which investigate in-vivo effect of two tranexamic acid doses on fibrinolysis parameters in adults undergoing cardiac surgery. One-way analysis of variance (ANOVA) was applied and the type I error was assumed by 0.05, we estimated that 7 patients were required for each group to provide 95% power to detect an effect of different doses of TXA on successively changing 33% of the activity of the fibrinolytic system when the standard deviation of coagulation proteins concentration was limited to within 20%. A target sample size of 30 was chosen based in this pilot investigation.
The variables with a normal distribution are reported as means ± standard deviations (SD), and continuous variables with a non-normal distribution are reported as medians (interquartile ranges). ANOVA followed by the Bonferroni test were used to compare continuous variables with a normal distribution, and Welch’s test was adopted when variance existed between the groups and the different time points. The homogeneity of variance was analyzed using Mauchly’s test of sphericity and corrected with the Greenhouse-Geisser test if variance existed. Differences in the concentrations of coagulation proteins between the groups measured at the same time points were analyzed using two-way ANOVA followed by the Bonferroni test. The Kruskal-Wallis H test was applied to continuous variables with a non-normal distribution. The Chi-squared or Fisher’s exact test followed by the Bonferroni test was used to analyze categorical data. All reported P values were two sided, and P values less than 0.05 were considered significant. Missing data was less than 10% and was not replaced. Intention to treat analysis was used and analysis was performed with SPSS version 18 (IBM, Armonk, NY) and G-Power (version 3.1; Informer Technologies, Inc.).