[Blood gas changes during laparoscopic cholecystectomy--comparative study of N2O pneumoperitoneum and CO2...

During laparoscopic cholecystectomy by alternative insufflation of nitrous oxide and carbon dioxide, the changes of blood gas tensions were measured and analyzed in 12 patients. During N2O insufflation, PaO2 decreased by about 25 mmHg and PaCO2 was unaltered compared with the values before pneumoperitoneum. While during CO2 insufflation, PaO2 decreased by about 13 mmHg and PaCO2 increased by about 6 mmHg. We considered that decrease in PaO2 during N2O insufflation was associated with not only uneven ventilation/blood flow ratios but also with the reduction in the alveolar O2 tension caused by the diffusion of N2O absorbed from the peritoneum. PaCO2 increases during CO2 insufflation because CO2 is absorbed from the peritoneum, and is not excreted entirely through the lungs.