Inert gas exchange of subcutaneous and intraperitoneal gas pockets in piglets

Subcutaneous and peritoneal tissue conductances for inert gases were measured in anesthetized Yorkshire piglets. Conductance spanned at least a 50-fold range in both subcutaneous and peritoneal tissues and showed the order: sulfur hexafluoride less than helium, neon less than ethylene less than nitrous oxide. Determination of conductance by measurement of composition changes within the gas space rather than the rate of pocket disappearance was particularly advantageous for the study of rapidly absorbed gases. Also, the simultaneous breathing of several inert gases substantially reduced interindividual variation by use of a reference gas. This study contains the first description of peritoneal gas exchange, including an estimate of effective peritoneal blood flow under conditions similar to laparoscopy. The critical role of diffusivity for discrimination between film and penetration models is discussed. More definitive modeling requires in vitro determination of tissue gas solubility and diffusivity.