In patients undergoing gynecologic laparoscopic surgery with trendelenburg position, the disturbance of pulmonary gas exchange frequently occurs due to high intra-abdominal pressure. The investigators tried to evaluate the effect of various inspiratory to expiratory ratio on pulmonary gas exchange by randomized controlled trial.

In patients undergoing gynecologic laparoscopic surgery with trendelenburg position, the disturbance of pulmonary gas exchange frequently occurs due to high intra-abdominal pressure. During the laparoscopic surgery with abdominal gas insufflation, gas exchange disturbance such as CO2 retention, hypoxemia occurs in addition to high plateau airway pressure. The usual strategy against these kinds of problem is pressure-controlled ventilation. However, the gas exchange problem especially CO2 retention can not be solved in some cases. The inverse-ratio ventilation (IRV), which prolongs the inspiratory time greater than expiratory time, can be applied for adult respiratory distress syndrome. The efficacy of IRV is to improve gas-exchange status by increasing mean airway pressure and alveolar recruitment. There have been several clinical investigations which applied IRV during general anesthesia. However, there have been debates about the effect of IRV during general anesthesia. Therefore, we tried to apply the IRV for subjects undergoing laparoscopic surgery, and evaluate the effect of different I:E ratio on the pulmonary gas exchange and respiratory mechanics.

Inclusion Criteria:

• patients undergoing elective gynecologic laparoscopic surgery
• the duration of pneumoperitoneum during laparoscopic surgery is more than 40 minutes

Exclusion Criteria:

• ASA (American society of anesthesiologists) classification of the subjects more than III.
• Age under 20, or more than 65 years.
• Past history of pneumothorax, COPD, asthma.
• Patients with ischemic heart disease, valvular heart disease.