There is no general agreement about the ideal gas for pneumoperitoneum. CO2, now in common use, has not compared to N2O sufficiently to disclose which one has minimal "physiological" invasiveness characters. Assigned randomly to carbon dioxide or nitrous oxide group, the hemodynamic and respiratory parameters (heart rate, mean arterial blood pressure, end-tidal CO2, minute ventilation, and O2 saturation) before pneumoperitoneum and during it were recorded. Pain, as perceived by patients, is measured 2, 4 and 24 hours after the procedure by visual analogue scale. Vomiting and use of analgesics and antiemetics were recorded and compared.

Inclusion Criteria:

• developed gallstones
• candidates for laparoscopic cholecystectomy
• written informed consent
• ASA Score = 1&2

Exclusion Criteria:

• signs and complications of gallstones in admission include acute cholecystitis and suppurative cholangitis
• complete Inability to move
• severe physical or mental disorders leading to inability to communicate -Pregnancy and
• cancer