The most common causes of bleeding are inadequate surgical hemostasis and reduced platelet number or function. Inadequate reversal of heparin and dilutional coagulopathy are less common, and heparin rebound is rare. Definitive diagnosis is difficult because of the limitations of coagulation investigations and because treatment may have to begin before test results are available if bleeding is brisk.

Inadequate hemostasis should be suspected when chest drain losses are excessive (> 300 ml/h) or prolonged and the coagulation profile is normal. Re-exploration should be considered early to prevent the problems of massive transfusion and circulatory instability due to hypovolemia and/or low oxygen-carrying capacity when blood loss is replaced with crystalloid and non-blood colloid.

Initial investigations include complete blood count, activated partial thromboplastin time, and prothrombin time. The activated clotting time may indicate inadequate reversal of heparin. Thromboelastography can also be used to guide therapy. Results of investigations should guide blood component treatment wherever possible and investigations should be repeated at intervals. Intravascular volume must be maintained while investigation and treatment of bleeding is instituted.

Many measures may be taken to conserve blood and reduce the coagulopathy associated with cardiopulmonary bypass. Apart from meticulous surgical hemostasis, hemologous blood use may be reduced by preoperative donation, intraoperative normovolemic hemodilution, and perioperative blood salvage. Coagulopathy is reduced by antifibrinolytics, biocompatible oxygenators and circuits, and accurate heparin reversal. It is possible to identify and, in some cases, treat preoperatively some patients who are at increased risk of bleeding. These include patients with bleeding diatheses, either congenital (hemophilia, von Willebrand's disease) or acquired (uremia, cirrhosis), those on anticoagulants such as warfarin, heparin, or aspirin, those receiving thrombolytics such as streptokinase up to the time of surgery, and those undergoing complex or prolonged surgery (reoperation, combined graft and valve surgery, surgery for aortic dissection). Although no coagulation test can predict which patients will bleed excessively postoperatively, hematological advice is valuable in the management of these complex cases.

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