Objective: To determine whether D-dimer fragments predictably increase during cardiopulmonary bypass (CPB), and if so, whether increases correlate with postoperative blood loss or predict postoperative coagulopathy. Design: Prospective observational study of 65 consecutive patients undergoing first-time coronary artery bypass graft (CABG) or first-time valve replacement. Setting: Single center University teaching hospital. Participants: Male and female patients between the ages of 30 and 90 years undergoing first-time CABG or valve replacement surgery using CPB. Patients were excluded from study for prolonged preoperative bleeding time, preoperative warfarin therapy, perioperative intra-aortic balloon pump support, thrombolytic therapy in the week preceding operation, reoperation, and emergency operation. Interventions: None. Measurements and Main Results: Blood sampling for platelet count, prothrombin time, partial thromboplastin time, thrombin time, fibrinogen, activated coagulation time (ACT) and D-dimer concentrations was obtained at four times during each case: (1) preoperatively, after insertion of the internal jugular introducer, before insertion of pulmonary artery catheter; (2) during CPB at 28 degrees C, immediately before rewarming; (3) after heparin neutralization (20 minutes after initial protamine dose); (4) 12 to 24 hours postoperatively. Blood loss in the intensive care unit was calculated by measuring total mediastinal drainage output at 1 and 4 hours after arrival from the operating room. An initial decrease in fibrinogen was noted during bypass, but no increase in D-dimer was identified. A few patients developed a modest increase in D-dimer after heparin neutralization, but none greater than 2.0 ug/mL. Postoperatively, fibrinogen concentration increased toward baseline levels. However, this is when six patients developed significant (>2.0 ug/mL) D-dimer formation. Results suggest appropriate physiologic response-normalization of fibrinogen with new synthesis and remodeling of clot in the operative site causing D-dimer formation. Patients with highest D-dimer levels at 12 to 24 hours postoperatively had the highest blood loss at 4 hours postoperatively, suggesting that early postoperative excess bleeding predisposed to increased clot formation and subsequent clot remodeling causing elevated D-dimer concentrations. Conclusions: D-dimer concentration is not usually elevated in patients undergoing CPB when adequately anticoagulated as monitored using the ACT. When mild elevation of D-dimer occurs, it is most often after heparin neutralization and/or in the postoperative period and is not predictive of increased postoperative blood loss. Elevations of D-dimer concentrations in the postoperative period without corresponding decreases in fibrinogen concentrations may occur and do not signify coagulopathy. Copyright (C) 1996 by W.B. Saunders Company
