RESUMO
INTRODUCTION: Heparin resistance during cardiopulmonary bypass poses a significant intraoperative dilemma. Antithrombin deficiency related heparin resistance is well described, but less common causes are still poorly understood and inadequately managed. CASE REPORT: We present a case of heparin resistance during cardiopulmonary bypass in a gentleman with no previous haematological history or thrombotic risk factors. The patient required three times the regular dose of unfractionated heparin to achieve acceptable conditions to initiate and maintain bypass. The patient was found to have elevated serum immunoglobulin M (IgM) kappa paraprotein on post-operative investigation. DISCUSSION: Paraproteins may exhibit non-specific binding to long polymeric chains of unfractionated heparin and inhibits the interaction between heparin and antithrombin. As a result, excessive doses of heparin are required to overcome this, which increases the risk of perioperative bleeding and other complications. CONCLUSION: Elevated serum paraprotein levels should be recognised as a cause of heparin resistance during cardiopulmonary bypass.