SIGNIFICANCE OF D-DIMER CONCENTRATIONS DURING AND AFTER CARDIOPULMONARY BYPASS

Objective: To determine whether D-dimer fragments predictably increase during cardiopulmonary bypass (CPB), and if so, whether increases cor relate with postoperative blood loss or predict postoperative coagulop athy. Design: Prospective observational study of 65 consecutive patien ts undergoing first-time coronary artery bypass graft (CABG) or first- time valve replacement. Setting: Single center University teaching hos pital. Participants: Male and female patients between the ages of 30 a nd 90 years undergoing first-time CABG or valve replacement surgery us ing CPB. Patients were excluded from study for prolonged preoperative bleeding time, preoperative warfarin therapy, perioperative intra-aort ic balloon pump support, thrombolytic therapy in the week preceding op eration, reoperation, and emergency operation. Interventions: None. Me asurements and Main Results: Blood sampling for platelet count, prothr ombin time, partial thromboplastin time, thrombin time, fibrinogen, ac tivated coagulation time (ACT) and D-dimer concentrations was obtained at four times during each case: (1) preoperatively, after insertion o f the internal jugular introducer, before insertion of pulmonary arter y catheter; (2) during CPB at 28 degrees C, immediately before rewarmi ng; (3) after heparin neutralization (20 minutes after initial protami ne dose); (4) 12 to 24 hours postoperatively. Blood loss in the intens ive care unit was calculated by measuring total mediastinal drainage o utput at 1 and 4 hours after arrival from the operating room. An initi al 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 l evels. However, this is when six patients developed significant (>2.0 ug/mL) D-dimer formation. Results suggest appropriate physiologic resp onse-normalization of fibrinogen with new synthesis and remodeling of clot in the operative site causing D-dimer formation. Patients with hi ghest D-dimer levels at 12 to 24 hours postoperatively had the highest blood loss at 4 hours postoperatively, suggesting that early postoper ative excess bleeding predisposed to increased clot formation and subs equent clot remodeling causing elevated D-dimer concentrations. Conclu sions: D-dimer concentration is not usually elevated in patients under going CPB when adequately anticoagulated as monitored using the ACT. W hen mild elevation of D-dimer occurs, it is most often after heparin n eutralization and/or in the postoperative period and is not predictive of increased postoperative blood loss. Elevations of D-dimer concentr ations in the postoperative period without corresponding decreases in fibrinogen concentrations may occur and do not signify coagulopathy. C opyright (C) 1996 by W.B. Saunders Company