Nitrous oxide fraction in the carbon dioxide pneumoperitoneum during laparoscopy under general inhaled anesthesia in pigs

During prolonged laparoscopy, the diffusion of other gases in the carbon dioxide (CO2) pneumoperitoneum may lessen its safely. Nitrous oxide (N2O)/CO2 gas mixtures may become hazardous with regard to gas embolization and fire risk. We therefore evaluated the kinetics of pneumoperitoneal intrusion of N2O. In five anesthetized domestic pigs, controlled ventilation, with an initial fraction of inspired oxygen = 1.0, was adjusted to keep ETco(2) pressure between 35 and 45 mm Hg. The peritoneum was insufflated with CO2 to a pressure of 12 mm Hg, which was maintained throughout the procedure. T0 was defined as the time when N2O was introduced in the breathing circuit (N2O end-tidal fraction = 66%). Gas samples (10 mL) from the pneumoperitoneum were analyzed every 10 min after T0. The N2O concentration was measured by using capillary gas chromatography coupled with mass spectrometry. Percentages of N2O in the CO2 increased with time (t) according to the ideal equation: N2O(t) = 66 (1 - exp(-0.005t)). In the peritoneal cavity, <2 h were required for the N2O to reach the concentration of 29%, which can support combustion. Eight hours to 10 h after T0, the intraperitoneal N2O fraction approaches the level of the N2O end-tidal fraction. Options to prevent accumulation of N2O are suggested. Implications: Pig models were used to evaluate the time course of nitrous oxide (N2O) diffusion in the pneumoperitoneum during nitrous oxide/oxygen anesthesia. Although peritoneal N2O concentration approaches the end-expiratory value after 8-10 h, it reaches 29% within 2 h. At this level, N2O is known to support combustion. Tnis N2O pollution should be prevented.