[Macroscopic infrared analysis of inhaled nitrous oxide diffusion to abdominal cavity in rats submitted to pneumoperitoneum.].

Background And Objectives: Nitrous oxide (N2O), for its tri-atomic asymmetric structure, has high energy emission and absorption characteristics within the infrared spectrum, with maximum absorption at 4.5 microm, what makes it visible at short infrared, when contrasted with a heat emission source (hot support). Many authors have described N2O diffusion to closed cavities by chromatography methods and gas analyzers, which do not allow a detailed macroscopic study of the gas. This study aimed at macroscopically filming in the infrared spectrum inhaled N2O diffusion to the peritoneal cavity of rats submitted to 20 mmHg room air pneumoperitoneum.

Methods: Animals where divided in three groups according to the anesthetic drug: I - Intravenous control: intraperitoneal thiopental; II - inhaled control: 1.2% isoflurane in 100% O2; III - nitrous oxide: 66% N2O in oxygen and 0.6% isoflurane. Thermal images of abdominal decompression where captured by an AGEMA 550 radiometer filmed at 7 frames per second.

Results: N2O was visible to infrared. At abdominal decompression, groups I and II have not shown visible gas traces at infrared thermographs, while group III had visible infrared traces.

Conclusions: Our conclusion was that 66% inhaled nitrous oxide has diffused to peritoneal cavity of rats submitted to 20 mmHg room air pneumoperitoneum, with no intra-abdominal pressure increase.