The study was approved by the institutional ethics committee of the University Hospital of the Canary Islands (La Laguna, Spain) and was conducted according to the Declaration of Helsinki. The study consisted of two parts.
Part 1: Assessment of postoperative incidence and protective/risk factors for inflammatory response after cardiopulmonary bypass
After obtaining informed written consent, we prospectively enrolled 191 consecutive Caucasian adult patients scheduled for cardiac surgery with CPB between January 2002 and February 2003. To avoid the effect of confounding factors on the IR, patients with endocarditis and those admitted with cardiogenic shock or with intra-aortic counterpulsation balloon were excluded (n = 26). Finally, a total of 165 patients were included. No patients received perioperative anti-inflammatory agents such as corticosteroids or nonsteroidal anti-inflammatory drugs.
IR was clinically defined as a core body temperature of greater than 38°C (100.4°F) in the first 4 hours after intervention, a systemic vascular resistance index of less than 1,600 dyn-seconds/cm5 per square meter, and a cardiac index of greater than 3.5 L/minute per square meter. VS was defined as persistent hypotension (mean arterial pressure of less than 70 mm Hg) requiring norepinephrine for at least 4 hours after failure to respond to appropriate volume expansion (pulmonary capillary wedge pressure of greater than 15 mm Hg). Serum concentrations of interleukin-6 (IL-6) were measured at 4 hours after CPB (Materials and methods, part 2). Risk factors associated with IR after CPB, including demographic variables, comorbid conditions, preoperative medication, duration of CPB, aortic crossclamp time, and the use of antifibrinolytic drugs, were investigated. Perioperative management of the groups was similar in the two studies (Materials and methods, part 2), except for the study medication. In this study, the surgeon decided when to use TA.
Part 2: Prospective double-blind trial of tranexamic acid effect on inflammatory response after cardiopulmonary bypass
We performed a randomized, double-blind, placebo-controlled study with consecutive Caucasian adult patients undergoing elective CPB surgery from February to May 2004. Postoperative care of the patients was performed in a 24-bed intensive care unit (ICU) at a university hospital. We excluded emergency interventions, patients with a history of chronic coagulopathy (prothrombin time [PT] of less than 50% or international normalized ratio of greater than 2 and platelets of less than 50,000/mm3 or aggregation dysfunction), renal failure (creatinine of greater than 2 mg/dL), chronic hepatopathy (Child B or higher degree), use of immunosuppressant drugs, endocarditis, sepsis in the first 24 hours after intervention, or unwillingness to enroll. Before CPB, participants had normal bleeding time, platelet collagen/epinephrine and collagen/ADP closure time, PT, activated partial thromboplastin time, and thrombin time. None of the patients received anti-inflammatory agents such as corticosteroids or nonsteroidal anti-inflammatory agents, including acetyl salicylate acid or clopidogrel or immunosuppressants, on the previous 5 days and the first 24 hours following intervention.
After informed written consent was obtained, patients were randomly assigned by independent pharmacists using a list of pseudorandomized numbers to receive coded infusions of either TA or placebo (0.9% saline) with doses of 2 g pre-CPB and post-CPB after protamine administration (using the same protocol as in the previous part of the study). The code was revealed once recruitment, data collection, and laboratory analyses were completed. The primary endpoint was to test the effect of TA on the incidence of IR and VS in patients undergoing elective CPB. Secondary endpoints were biological parameters related to inflammation, coagulation, and fibrinolysis systems.
Demographic variables, comorbid conditions, perioperative clinical data, and postoperative outcomes (IR, VS, duration of mechanical ventilation, postsurgical ICU stay and hospital stay, and mortality) were recorded. Core body temperature, biochemical determinations (hematology, inflammation, coagulation, and fibrinolysis), and hemodynamic parameters were recorded before intervention (baseline), on admission to the ICU after surgery (0 hours), and at 4 hours and 24 hours after intervention. In addition, blood loss measured by tube chest drainage and the amount of hemoderivatives used, as well as its frequency, were collected after intervention at the above time points and when chest tubes were removed (defined as total bleeding). Surgical risk was calculated by Parsonnet score.
Anesthetic procedures were standardized and consisted of an opioid-based anesthetic supplemented with volatile anesthetic and muscle relaxants. All interventions were performed by the same surgical team with wide experience in these surgical interventions. All patients were preoperatively monitored with a pulmonary artery continuous thermodilution catheter (Edwards Lifesciences LLC, Irvine, CA, USA). Neither heparin-coated circuits nor leukocyte filters were used. The extracorporeal circuit consisted of a hardshell membrane oxygenator (Optima XP; Cobe, Denver, CO, USA, or Quantum Lifestream International, Inc., Woodlands, TX, USA), a Tygon™ (Dideco s.r.l., Mirandola, Italy) extracorporeal circuit, and a Medtronic™ Biopump (Medtronic, Inc., Minneapolis, MN, USA) centrifugal pump. Below hypothermic temperatures of 28°C to 30°C, the pump flow was adjusted to maintain a mean arterial pressure of greater than 60 mm Hg and a flow index of 2.2 L/minute per square meter. Myocardial protection was achieved using antegrade, cold, St. Thomas 4:1 sanguineous cardioplegia. The circuit was primed with 30 mg of heparin followed by an initial dose of 3 mg/kg and further doses when necessary to achieve and maintain an activated clotting time of 480 seconds. To reverse the effect of heparin, protamine was used based on blood heparin levels measured by Hepcon® (Medtronic, Inc.). A blood salvage device was used in all patients. The transfusion trigger was a hemoglobin threshold of less than 8 g/dL, PT of less than 50%, and platelets of less than 50,000/mm3. Fluid management was carried out to achieve 8 to 12 mm Hg of central venous pressure or 12 to 15 mm Hg of pulmonary artery occlusion pressure at zero positive end-expiratory pressure by infusions of crystalloids and colloids. Catecholamine support, when necessary, was used as follows: Norepinephrine was titrated to achieve a mean arterial pressure of greater or equal to 70 mm Hg, and dobutamine was titrated to achieve a cardiac index of greater or equal to2.5 L/minute per square meter. Amines were tapered off in steps of 0.02 and 1 μg/kg per minute, respectively.
Soluble tumor necrosis factor receptor (STNFR)-1 and IL-6 (normal range: less than 5.9 pg/mL; intra-assay variation: 4.5%) were measured using an automatic immunoenzyme assay system (IMMULITE ONE™; Diagnostic Products Corporation, now part of Siemens AG, Munich, Germany). STNFR-1 EASIA (normal range: 3.4 to 10.8 ng/mL; intra-assay variation: 1.7%) are solid phase enzyme-amplified sensitivity immunoassays performed on a microtiter plate (, Biosource Technologies, Inc., Fleunes, Belgium).
Coagulation and fibrinolysis determination
Quantitative plasminogen activator inhibitor 1 (PAI-1) antigen (normal range: 2 to 47 ng/mL; intra-assay variation: 3.7%) and tissue plasminogen activator antigen levels (normal range: less than 9.0 ng/mL; intra-assay variation: 4.2%) were measured using an enzyme-linked immunosorbent assay (IMUBIND®; American Diagnostica Inc., Stamford, CT, USA). D-dimer (normal range: less than 300 ng/mL; intra-assay variation: 3%) was measured using an immunoturbidimetric test (D-dimer PLUS; Dade Behring, now part of Siemens AG).
Comparisons between groups (patients with and without IR or the TA group versus placebo group) were performed using the Pearson χ2 test or Fisher exact test for categorical variables and the Student t test or the Mann-Whitney U test for continuous variables, as appropriate. Logistic regression analysis (forward stepwise conditional) was used to identify independent risk factors associated with IR. Initially, only variables with a P value of less than 0.15 (TA, clamping time, and mixed cardiac surgery) in the univariate analysis were incorporated. To perform the controlled study, a sample size of 100 patients was required to detect a statistically significant reduction of at least 20% in IR by TA. Assuming an incidence of 30% in the placebo group, a study population of 100 patients was expected to have 80% power to detect a 20% reduction in IR. For primary endpoint outcomes, all differences in preoperative variables with a P value of less than 0.15 in the univariate analysis of the controlled study were entered into a logistic regression analysis. Results for qualitative variables are expressed as frequency and percentage. Quantitative variables are expressed as mean ± standard deviation or as median and interquartile range in the case control study and as mean and 95% CI in the controlled study. A P value of less than 0.05 was considered statistically significant. For primary endpoint outcomes of the controlled study, exact P values are reported. SPSS version 12.2 (SPSS Inc., Chicago, IL, USA) was used.