Median blood loss was 800 ml ( range 300 to 1,600 ) in 55 of 163 patients ( 34 % ) with pelvic venous pressure less than 5 mm Hg and 1,200 ml ( range 400 to 3,000 ) in 108 of 163 ( 66 % ) with pelvic venous pressure 5 mm Hg or greater ( p < 0.0001 ) .