Perioperative outcome
The average operative times was 249 minutes for the low-, mid- and high-volume groups, at 270 minutes, 260 minutes and 227 minutes, respectively (P < 0·001). Although there was no significant difference in operative time between the low- and mid-volume groups, that of the high-volume group was significantly shorter than that of the low-and mid-volume groups (P < 0·001). Among the 1405 patients, the average intraoperative blood loss was 196 ml; the values were 218 ml, 197 ml and 179 ml in the low-, mid- and high-groups, respectively (P = 0·005). There was no significant difference between the mid-volume group and the low- and high-volume groups, but blood loss in the high-volume group was significantly less than that in the low-volume group (P = 0·001).