Alteration of the hydrogen ion concentration according to the gas used forpneumoperitoneum (CO2, helium, air, xenon, N2O)

Background: According to the literature a possible reason for trocar metast ases after laparoscopy is the alteration of the subcutaneous hydrogen ion c oncentration (pH). The influence of the pH on the cell function (macrophage s, T-cells) has been described. Our aim was the objectivation and verificat ion of this thesis by measuring subcutaneous pH using different gases (CO2, helium, xenon, air, N2O) for the pneumoperitoneum. Methods: Subcutaneous pH was measured by tonometry and pH-metry in the subc utaneous fat tissue of male wistar rats (350 g, 5 per group). The intraabdo minal pressure was 0, 3, 6, 9 mmHg using 30 mins as equilibration time for each gas. Statistical analysis was performed by ANOVA and the student t-tes t. Results: In the ANOVA there were significant differences between the gases in relation to the intraabdominal pressure (p = 0.001). At 6 mmHg the subcu taneous pH was 7,29 for Xenon, 7,28 for N2O, 7,27 for air, 7,31 for helium and 7,03 for CO2. Comparing helium and CO2 the p-value was 0.0004 in the t- test. At 9 mmHg the results were even more significant. Conclusion: The alteration of the pH of the subcutaneous fat tissue differs depending on the kind of gas (CO2, N2O, helium, air, xenon) used for the p neumoperitoneum. Our results suggest a possible explanation for the frequen t subcutaneous metastases after laparoscopy with CO2.