Design
Two prospective and observational cohorts were assessed in the Marienhospital Bottrop and the University Hospital Frankfurt between January 2015 and September 2017. Data were merged for publication.
Patients (>= 18 years) undergoing elective orthopedic or cardiac surgery with expected blood loss > 10% of body blood volume were included. Exclusion criterion was pregnancy.
Outcome
The primary outcomes were red cell separation performance and washout quality. Red cell separation performance was defined as sufficient if haematocrit (Hct) values of the autologous packed red cell (PRC) concentrate reached a target range between 55 and 75% according to the current German Guidelines [5]. Washout quality was defined as sufficient if the removal ratio (RR) reached target range between 80 and 100%. Washout quality was evaluated for potassium (K+), albumin (Alb), heparin (aXa), free hemoglobin (fHb), white blood cells (WBC), and platelets (Plt). Calculation of RRs was based on the following formula: RR [%] = [1-(VPRC x {Sub}PRC)/(VRES x {Sub}RES)] × 100 [%] (VPRC=PRC volume; VRES=Shed blood volume; {Sub}PRC = concentration of a substance in PRC volume; {Sub}RES = concentration of a substance in shed blood in reservoir).
Procedures
After collection of a minimum of 400 ml shed blood during surgery, shed blood was processed by a CE-certified autotransfusion device (CATSmart®, Fresenius Medical, Germany). The shed blood was collected in a sterile reservoir, was processed in a continuous running centrifuge for red cell separation and washed using the smart wash mode (standard wash program, packed red cells output rate 20-40 ml/min). The product was a sterile bag filled with washed packed red cells for reinfusion into the patient. During this process all plasmatic and non-erythrocyte cellular components of the collected blood, and thus activated coagulation factors, products of fibrinolysis and cell trauma as well as the anticoagulant were removed. The Hct of the incoming shed blood and outgoing washed PRC is measured and visualized on the device screen, for information. To characterize Hct values, blood samples were taken from the CATSmart reservoir and the PRC concentrate, according established procedures before and after the washing step and analyzed in the central laboratory (LAB). Blood reservoir was manually homogenized before blood sampling.
Statistical analysis
Data are provided as median, 25% quartile and 75% quartile when indicated, and a p-value of ≤0.05 was considered as statistically significant. RR of K+, Alb, aXa, fHb, WBC, and Plt were calculated for each patient. Correlation coefficient was determined by Spearman. Microsoft Excel 2010 was used for all statistical calculations. A minimum of 20 patients was defined as sufficient for this descriptive analysis.