The refrigerated supernatant was sent the next day to Hema-Quebec for a second centrifugation at 5000 xg for 7 min and the measurement of free haemoglobin(Hb_f)using a HemoCue Plasma/Low HB photometer(HemoCue, Angelholm, Sweden).The percentage of haemolysis was calculated using the standard formula:(1-Hct)*(Hb_f/Hb_t).The potassium level of each sample was measured using a blood gas analyser(GEM3000, Instrumentation Laboratory, Bedford, MA, USA).From previous studies conducted in 2013[10, 25], we expected the average haemolysis rate in the packed RBCs to be approximately 0.25%.Setting the power of our study to 80%, at least 16 measurements for the same flow rate were required to detect an increase in the level of haemolysis above 0.8%, assuming a hypothetical standard deviation of 0.55.However, to detect a statistically significant(P