AM25-SN-29-L - Cold Truths: The Potential Hidden Impact of “Clinically Insignificant” Antibodies in Hypothermic Cardiac Surgery

Proposed Session Description: Cold RBC autoantibodies are a common laboratory finding that can interfere with routine ABO/RhD typing and RBC alloantibody detection. While they can cause hemolytic anemia, such cold RBC autoantibodies can also be clinically insignificant in part because humans do not spend time at such low body temperatures.

Hypothermic cardiac surgical procedures, though, can expose patients to prolonged temperatures far below those of normal daily living. Cardiopulmonary bypass as a surgery has shifted from large, open circuits to refined heparin-bonded systems that support more targeted interventions, however the basics remain the same. Cold cardioplegia solutions used to arrest the heart intraoperatively have evolved from only 4°C solutions that are mixed directly with patient blood prior to instillation to include warmer formulations. Systemic patient hypothermia can reach temperatures as low as 16°C in procedures requiring complete circulatory arrest. Under such conditions, a patient’s cold RBC autoantibody, while usually asymptomatic, can trigger massive hemagglutination, myocardial infarction, and renal failure.

Standard RBC antibody screening is not routinely performed at such lower temperatures and hence potentially harmful cold RBC autoantibodies can go undetected preoperatively. Each cold RBC autoantibody also has a variable temperature range for its activity that can only be elucidated with formal thermal amplitude testing. Furthermore, strength of cold RBC autoantibody reactivity and potential intraoperative effect do not clearly correlate making definitive prediction of any potential harm challenging to both surgeons and laboratorians alike.

In this session, we will explore some unique surgical techniques and key thermic features of cardiovascular surgery and the rare catastrophic effect that a cold RBC autoantibody may have. We will explain the thermal amplitude testing process and present laboratory data showing the wide variety of thermal amplitude patterns amongst cold RBC autoantibodies and their correlation (or lack thereof) with 4°C cold agglutinin titers. Finally, we will walk through cold RBC autoantibody thermal amplitude results and describe potential intraoperative mitigation strategies that would be considered.