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 safety. 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 ETCO₂ 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. This N₂O pollution should be prevented.