The median lifespan of the first study circuit in each patient was 39.2 hours ( 95 % CI , 32.1-48 .0 hr ) in the citrate and calcium group versus 22.8 hours ( 95 % CI , 13.3-34 .0 hr ) in the heparin and protamine group ( log rank p = 0.0037 , 204 circuits ) .