Methods Patients are randomized into two groups. Group A: after induction of general anesthesia, in supine position a pneumoperitoneum is induced with carbon dioxide insufflation through a surgical inserted trocar into the abdominal cavity, then patients are positioned in steep trendelenburg at 25 degrees head down. Group B: after induction of general anesthesia, patients are positioned in steep trendelenburg position at 25 degrees head down, then a pneumoperitoneum is induced with carbon dioxide insufflation through a surgical inserted trocar into the abdominal cavity.