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Background: Intraoperative cell salvage (ICS) is an autologous blood conservation technique that allows the collection and reinfusion of a patient's blood that is lost during surgery. ICS can reduce the need for allogenic blood and has advantages including: (i) reduced risk of transfusion reactions, (ii) improved immune competence, and (iii) reduced post-operative infection risk. However, ICS is not a passive process and blood undergoes processing, centrifugation and filtration. Extracellular vesicles (EVs) are small, lipid bound particles that are released by cells and are present in biological fluids including blood. The number, cellular origin and function of EVs have been characterised in allogenic blood components, but our understanding of the changes in EVs during the ICS process remains limited. Methods: Nineteen elective orthopaedic patients, with the potential for significant blood loss, were recruited and consented to receive ICS (ethics: RBWH [HREC/17/QRBW/685). Thirteen of these patients received autologous ICS blood. ICS blood was sampled following initial collection and processing (pre-filtration) and before reinfusion into the patient (post-filtration). For characterization of EVs, samples of ICS blood were centrifuged twice (3000 g, 15 min) to obtain the supernatant which was stored at −80°C. Samples of thawed ICS supernatant were diluted in phosphate buffered saline, then analyzed using the Nanosight NS300 to determine the concentration and size distribution of EVs(). EV concentration was determined, and pre- and post- filtration compared using Wilcoxon matched pairs test. Mean and mode of particle size were determined, and pre- and post- filtration results compared using paired T-test. n = 10/13 patients analyzed. Results: ICS blood contained a median of 7.37 × 109 EVs/mL (IQR 5.51 × 109–9.89 × 109) in the pre-filtered product and 5.90 × 109 EVs/mL (IQR 4.34 × 109–1.19 × 1010) in the filtered product for reinfusion into the patient. Overall, there was no difference in EV concentration before and after filtration, although considerable differences in the EV concentration were observed between individuals. The mean particle size and distribution was also similar before and after filtration of the ICS blood (prefiltration size 149 nm [SD 11] and post-filtration size 148 nm [SD 10]; mode size distribution 129 nm [SD 11] for pre-filtered ICS blood and 127nm [SD 14]). EVs were present in ICS blood. Our preliminary results indicate standard filtration of the ICS blood prior to reinfusion did not result in significantly altered EV size, distribution nor concentration, although considerable inter-individual differences were evident. In the next phase of the project, the cellular origin of the EVs will be determined by flow cytometry and the profile of EVs in ICS will be compared to allogenic blood during routine storage.