BACKGROUND: Introduction of a pneumoperitoneum using CO2 is accompanied by significant alterations in respiratory function and pulmonary gas exchange during laparoscopic cholecystectomy. Previous studies have shown differing results concerning pulmonary gas exchange: a significant decrease of PaO2 was induced with isoflurane. In contrast, no significant changes were observed with propofol. The purpose of the present study was to compare the effects of propofol vs isoflurane on pulmonary gas exchange during general anesthesia for laparoscopic cholecystectomy. METHODS: Forty patients were divided randomly between isoflurane and propofol groups. After induction of anesthesia, ventilation was controlled and intra-abdominal pressure was maintained automatically at 12 mmHg by a CO2 insufflator. After the measuring of baseline values of blood pressure, heart rate, PaO2, PaCO2 and PetCO2 before CO2 insufflation, measurements were also made immediately, 30min after CO2 insufflation and 5 min after CO2 exsufflation. RESULTS: In the isoflurane group, PaCO2, PetCO2, PaO2, and P(a-et)CO2 changed significantly 30 min after CO2 insufflation and 5 min after CO2 exsufflation (P < 0.05). In the propofol group, PaCO2 and PetCO2 increased significantly 30 min after CO2 insufflation and 5 min after CO2 exsufflation (P < 0.05), but PaO2 and P(a-et)CO2 remained constant. When the two groups were compared, there were significant differences in PaO2, PaCO2, PetCO2 and P(a-et)CO2 at 30min after CO2 insufflation and 5 min after CO2 exsufflation (P < 0.05). CONCLUSIONS: These results indicate that during laparoscopic cholecystectomy the PaO2 was significantly lower and PaCO2 and P(a-et)CO2 were significantly higher in the isoflurane group compared with the propofol group.