In 1,759 evaluated total hip - and knee-replacement surgery patients , the mean erythrocyte use was 0.19 ( SD , 0.9 ) erythrocyte units/patient in the autologous group ( n = 1,061 ) and 0.22 ( 0.9 ) erythrocyte units/patient in the control group ( n = 698 ) ( P = 0.64 ) .