Annexin V Positive Microvesicles Are Elevated and Correlate with Flow Rate in Patients Receiving Veno-Arterial Extracorporeal Membrane Oxygenation

OBJECTIVES: Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is used in critically ill patients requiring haemodynamic support. Microvesicles (MV) are released by activated blood cells acting as mediators of intercellular communication. We aimed to determine MV count and composition over time in patients with VA-ECMO and explore what drives MV formation. METHODS: VA-ECMO patients and healthy controls were recruited prospectively, and blood was taken at different time points (day 0, 1, 3 after ECMO placement and after explantation) for MV analysis. RESULTS: Annexin V positive MV were increased in patients (n = 14, mean age = 61.4 +/- 9.0 years, 11 males, 3 females) compared to healthy controls (n = 6, Annexin V positive MV count per millilitre day 1 versus healthy controls: 2.3 x 10(6) vs 1.3 x 10(5), P < 0.001). Furthermore, patients had higher proportions of endothelial and leukocyte MV [leukocyte MV day 1 versus healthy controls (%): 32.8 vs 17.5, P = 0.001; endothelial MV day 1 versus healthy controls (%): 10.5 vs 5.5, P = 0.01]. Annexin V positive and leucocyte MV correlated with the flow rate (r = 0.46, P = 0.01). CONCLUSIONS: Patients on VA-ECMO have increased levels of circulating MV and a changed MV composition. Our data support the hypothesis that MV release may be driven by higher flow rate and cellular activation in the extracorporeal circuit leading to poor outcomes in these patients.