The effects of cardiopulmonary bypass on fibrin formation and lysis: is a normal fibrinolytic response essential?

PAI-1 and t-PA/PAI-1 complex potential markers of fibrinolytic bleeding after cardiac surgery employing cardiopulmonary bypass

Background

Enhanced bleeding remains a serious problem after cardiac surgery, and fibrinolysis is often involved. We speculate that lower plasma concentrations of plasminogen activator inhibitor – 1 (PAI-1) preoperatively and tissue plasminogen activator/PAI-1 (t-PA/PAI-1) complex postoperatively might predispose for enhanced fibrinolysis and increased postoperative bleeding.

Methods

Totally 88 adult patients (mean age 66 ± 10 years) scheduled for cardiac surgery, were enrolled into a prospective study. Blood samples were collected pre-operatively, on admission to the recovery and at 6 and 24 hours postoperatively. Patients with a surgical bleeding that was diagnosed during reoperation were discarded from the study. The patients were allocated to two groups depending on the 24-hour postoperative chest tube drainage (CTD): Group I > 500ml, Group II ≤ 500ml. Associations between CTD, PAI-1, t-PA/PAI-1 complex and D-dimer were analyzed with SPSS.

Results

Nine patients were excluded because of surgical bleeding. Of the 79 remaining patients, 38 were allocated to Group I and 41 to Group II. The CTD volumes correlated with the preoperative plasma levels of PAI-1 (r = − 0.3, P = 0.009). Plasma concentrations of preoperative PAI-1 and postoperative t-PA/PAI-1 complex differed significantly between the groups (P < 0.001 and P = 0.012, respectively). Group I displayed significantly lower plasma concentrations of fibrinogen and higher levels of D-dimer from immediately after the operation and throughout the first 24 hours postoperatively.

Conclusions

Lower plasma concentrations of PAI-1 preoperatively and t-PA/PAI-1 complex postoperatively leads to higher plasma levels of D-dimer in association with more postoperative bleeding after cardiac surgery.

Systematic elucidation of effects of tranexamic acid on fibrinolysis and bleeding during and after cardiopulmonary bypass surgery

The aim of this study was to systematically elucidate the effects of tranexamic acid on fibrinolysis and bleeding during and after cardiopulmonary bypass (CPB) surgery. Twenty-two patients undergoing CPB surgery were randomized to receive 100 mg/kg tranexamic acid or an equal volume of saline after anesthesia induction and prior to skin incision. Plasma levels of tissue plasminogen activator (t-PA) antigen and activity, crosslinked fibrin degradation products (D-dimer), alpha2-antiplasmin-plasmin complex, and plasminogen activator inhibitor-1 (PAI-1) antigen were measured. Blood samples were obtained after induction of anesthesia, before, during, and after CPB, at the end of surgery, and the next morning after surgery. Intraoperative and postoperative blood loss during 24 h after surgery was recorded. Patients' demographics were similar between the two groups. No patients suffered from thrombotic complications after surgery. In the tranexamic acid group, fibrinolytic activity and secondary fibrinolysis as measured by t-PA activity and D-dimer were markedly suppressed during CPB surgery (P=.042 and P=.015, respectively). Decreased fibrinolytic activity and fibrinolysis were accompanied by reduction of perioperative bleeding in the tranexamic acid group. We could also find a good positive correlation between the peak levels of t-PA activity and D-dimer (r(2)=.4203, P=.0011). No differences in the t-PA antigen, PAI-1 antigen release, and plasmin inhibition by alpha2-antiplasmin were apparent between the two groups. In a randomized, prospective trial of patients undergoing CPB surgery, we demonstrated that the synthetic antifibrinolytic drug tranexamic acid effectively suppresses fibrinolysis by inhibiting t-PA and plasmin activity with clear reduction of perioperative blood loss. While tranexamic acid had no effects on the other important fibrinolytic inhibitors like PAI-1 and alpha2-antiplasmin.

Leucodepletion during cardiopulmonary bypass reduces blood transfusion and crystalloid requirements

Cardiopulmonary bypass (CPB) is associated with the production of inflammatory responses, which can have significant influence on prognosis. We studied the effects of leucocyte-depletion filters on inflammatory parameters and early postoperative prognosis during coronary revascularization. Twenty patients undergoing elective coronary revascularization were randomly divided into two groups. Ten patients had leucocyte-depletion filters added to the CPB circuit (treatment group) and 10 were used as control cases (control group). Expression of CD11b on neutrophils, and production of myeloperoxidase and lactoferrin, were measured in arterial samples between induction and 3 h postbypass. In addition, clinical parameters were measured during inpatient recovery. CD11b neutrophil expression, and myeloperoxidase and lactoferrin production, were found to be upregulated during CPB and then to decline to preoperative levels by the third postoperative hour. Blood transfusion requirements were reduced in the treatment group, equalling 1.5 +/- 1.2 units, compared to 2.7 +/- 1.1 units for the control group (p value = 0.034) and so were the volumes of crystalloid infused during the first 24 h postoperatively, equalling 3.9 +/- 1.21 in the treatment group and 3.3 +/- 0.71 in the control group (p value = 0.021). Overall, the application of leucocyte depletion produced an early clinical advantage, underlining the need for an improved understanding and manipulation of the inflammatory response to CPB.

Intraoperative local fibrinolysis as emergency therapy after early coronary artery bypass thrombosis

OBJECTIVE

Acute graft occlusion early postoperatively after coronary artery bypass grafting (CABG) is a rare but dramatic complication, frequently making resuscitation necessary. Emergency reoperation with reanastomosing of the concerning grafts is the normal procedure to restrict the otherwise unavoidable myocardial damage. Mortality in these cases is up to 50%. Due to this unsatisfying situation, we perform since 1995 in such cases an adjuvant intraoperative intracoronary installed fibrinolysis with recombinant tissue type plasminogen activator (rt-PA; alteplase).

METHODS

Between 1/1994 and 8/1998, 4231 patients underwent CABG. In 18 of these patients, emergency reoperation within the first 12 h after CABG due to clinical signs of acute myocardial infarction was necessary. In nine of the patients (group II) additionally intraoperative rt-PA lysis of the involved vessel/s has been performed. When the peripheral anastomosis was reopened and the thrombotic material was removed, we inserted for this a left atrial-catheter (LA-catheter) of 1.2 mm in diameter, into the coronary artery. Then we administered within 3-5 min, up to 100 mg rt-PA (t1/2: 5-9 min.) locally into the vessel. All patients were treated postoperatively with acetylsalicyl acid (ASA) and heparine.

RESULTS

In group I (n = 9; seven males, two females) without thrombolytic therapy, 78% of the patients (n = 7) could not have been prevented from large myocardial infarction despite emergency reoperation. Three of these patients died during or early after reintervention. In group II with fibrinolytic therapy (n = 9) three of the patients developed Q-wave myocardial infarction following reoperation. None of the patients died. Creatinkinase maximum were in group I significantly higher than in group II (group I: CK = 1254 units/I, CK-MB = 197 units/l; group II: CK = 502 units/l, CK-MB = 61 units/l; P < 0.01). Postoperative bleeding was considerable elevated in both groups. In group I, 832 ml/24 h (375-1420 ml), in group II 1164 ml/24 h (520-1560 ml). Lysis-associated complications were not observed.

CONCLUSIONS

Reoperation of patients with acute thrombotic bypass occlusion after CABG is characterized by a high mortality and morbidity. If additionally fibrinolysis is performed, a sufficient myocardial perfusion seems to be restored. A short half-life in combination with the presented non-systemic application technique of rt-PA seem to prevent unpredictable bleeding. Rt-PA lysis apparently contributes very effectively to the restoration of the macro- and microcirculation within the infarct-related area. Thrombolytic therapy during cardiac surgery with rt-PA is feasible, its application easy and harmful complications are not seen.

Endothelial Cell-Blood Interface Actions and the Procoagulant Response

Anesthesiologists and surgeons have focused on the problems of hypocoagulability and resulting hemorrhage after cardiopulmonary bypass. Recent work in endothelial cell biology has demonstrated that the interaction of inflammatory processes and coagulation dysfunction with the endothelium may contribute to either hypocoagulability (bleeding) or hypercoagulability (thrombosis). New work with endothelial cell function and intracellular signaling of procoagulant responses may allow for unique therapeutic interventions in the future.

Endothelial cell injury in cardiovascular surgery

In the last decade the endothelium has been shown to play a major role in regulating membrane permeability, lipid transport, vasomotor tone, coagulation, inflammation, and vascular wall structure. These critical endothelial cell functions are extremely sensitive to injury in the form of hypoxia, exposure to cytokines, endotoxin, cholesterol, nicotine, surgical manipulation, or hemodynamic shear stress. In response to injury endothelial cells become activated, tipping the balance of endothelial-derived factors to disrupt barrier function, and enhance vasoconstriction, coagulation, leukocyte adhesion, and smooth muscle cell proliferation. Although these responses likely exist as protective mechanisms, if the stimuli are severe the responses may become excessive, resulting in damaged tissue, impaired organ function, and an abnormal fibroproliferative response. Recent discoveries in the field of vascular biology have led to an expanded understanding of many of the complications of cardiovascular operations. Because of the wide impact endothelial cell dysfunction has on patients with cardiovascular disease, issues pertaining to endothelial biology are in the forefront of research that will affect the current and future practice of cardiothoracic surgery.