The Effect of Prolonged Inspiratory Time on Gas Exchange During Robot-assisted Laparoscopic Surgery With Steep Trendelenburg Position : A Crossover Randomized Clinical Trial

Gas exchange disturbance frequently occurs in steep Trendelenburg position during robot-assisted laparoscopic prostatectomy or cystectomy. Due to increased intrathoracic pressure and absorbed CO2 gas insufflated into abdominal cavity, hypercapnia as well as hypoxia may occur. Inverse ratio ventilation or prolonged inspiratory time during mechanical ventilation has been reported to be improve gas exchange in adult respiratory distress syndrome. The investigators attempt to test the hypothesis that prolonged inspiratory time (I:E ratio = 1:1) may improve the gas exchange during robot-assisted laparoscopic urologic surgery.

Inclusion criteria

• American Society of Anesthesiologists physical status class I-II and scheduled for an elective robot-assisted laparoscopic radical prostatectomy or robot-assisted laparoscopic radical cystectomy
• Patients who voluntarily decides to participate in the trial and has agreed in written informed consent

Exclusion criteria

• Patients with the anatomical abnormalities of respiratory system(abnormal airway anatomy, severe scoliosis, post-pneumonectomy state), severe chronic respiratory diseases, chronic obstructive pulmonary disease (COPD), asthma, heart failure, obesity ( Body Mass Index [BMI] > 30kg/m2), severe hepatic failure or renal failure