Lupus Anticoagulant and Cardiopulmonary Bypass

Patients with lupus anticoagulant (LA), with or without antiphospholipid syndrome (APS) requiring cardiopulmonary bypass (CPB), present a unique set of clinical challenges. These include LA interference with unfractionated heparin (UFH) monitoring by the activated clotting time (ACT) as well as the risk of both circuit and systemic thrombosis. LA is one of the heterogeneous group of antiphospholipid antibodies.[1] Although LA causes prolongation of activated partial thromboplastin time (aPTT) and ACT in vitro assays, persistently positive LA is associated with increased risk of thrombosis.[1] The ACT is a point-of-care test used to assess the adequacy of heparinization and is monitored every 30 to 40 minutes during bypass by the anesthetic team. It is known that the ACT poorly correlates with the plasma heparin level and does not accurately predict the protamine sulfate dose needed for reversal of UFH following termination of CPB.[2] Previously we have demonstrated that patients without LA undergoing CPB have a poor correlation between ACT and heparin anti-Xa levels.[3] Although monitoring the inhibition of factor Xa by heparin is the gold standard for measuring the anticoagulant effect of UFH, it is not widely available in many hospital laboratories and providing heparin anti-Xa levels to assess the heparin levels in a timely manner for patients undergoing CPB is not always practical. Therefore, the ACT remains the main measure for monitoring the anticoagulant effect of UFH during CPB. Inaccurate assessment of anticoagulant effect of UFH with ACT[3] is further complicated by the presence of LA that may independently prolong the ACT and may be present in up to 5% of otherwise healthy patients.[4]