Significant differences were reported in mean hemoglobin loss ( -1.03 and -2.18 g/dL ) , mean operative time ( 86.16 and 111.7 minutes ) , and mean hospital stay ( 49.88 and 81.2 hours ) in the supine and prone positions , respectively , and anesthesiological parameters ( the mean blood pressure decreased by 2 and 14.06 mm Hg , the mean heart rate changed by -0.82 and +13.28 beat/minute , and the peak air way pressure changed by +1.08 cm H2O and +7.56 cm H2O in the supine and prone positions , respectively ) .