Shear Forces Induced Platelet Clearance Is a New Mechanism of Thrombocytopenia

Background: Thrombocytopenia has been consistently described in patients with extracorporeal membrane oxygenation (ECMO) and associated with poor outcome. However, the prevalence and underlying mechanisms remain largely unknown, and a device-related role of ECMO in thrombocytopenia has been hypothesized. This study aims to investigate the mechanisms underlying thrombocytopenia in ECMO patients.Methods: In a prospective cohort of 107 ECMO patients, we investigated platelet count, functions, and glycoprotein shedding. In an ex vivo mock circulatory ECMO loop, we assessed platelet responses and VWF (von Willebrand factor)-GP Ib alpha (glycoprotein Ib alpha) interactions at low- and high-flow rates, in the presence or absence of red blood cells. The clearance of human platelets subjected or not to ex vivo perfusion was studied using an in vivo transfusion model in NOD/SCID (nonobese diabetic/severe combined Immunodeficient) mice.Results: In ECMO patients, we observed a time-dependent decrease in platelet count starting 1 hour after device onset, with a mean drop of 7%, 35%, and 41% at 1, 24, and 48 hours post-ECMO initiation (P=0.00013, P<0.0001, and P<0.0001, respectively), regardless of the type of ECMO. This drop in platelet count was associated with a decrease in platelet GP Ib alpha expression (before: 47.8 +/- 9.1 versus 24 hours post-ECMO: 42.3 +/- 8.9 mean fluorescence intensity; P=0.002) and an increase in soluble GP Ib alpha plasma levels (before: 5.6 +/- 3.3 versus 24 hours post-ECMO: 10.8 +/- 4.1 mu g/mL; P<0.0001). GP Ib alpha shedding was also observed ex vivo and was unaffected by (1) red blood cells, (2) the coagulation potential, (3) an antibody blocking VWF-GP Ib alpha interaction, (4) an antibody limiting VWF degradation, and (5) supraphysiological VWF plasma concentrations. In contrast, GP Ib alpha shedding was dependent on rheological conditions, with a 2.8-fold increase at high- versus low-flow rates. Platelets perfused at high-flow rates before being transfused to immunodeficient mice were eliminated faster in vivo with an accelerated clearance of GP Ib alpha-negative versus GP Ib alpha-positive platelets.Conclusions: ECMO-associated shear forces induce GP Ib alpha shedding and thrombocytopenia due to faster clearance of GP Ib alpha-negative platelets. Inhibiting GP Ib alpha shedding could represent an approach to reduce thrombocytopenia during ECMO.