Oncological effects of insufflation with different gases and a gasless procedure in rats

Background: The validity of using carbon dioxide (CO₂) pneumoperitoneum in laparoscopic tumor surgery has not been investigated thoroughly. The oncologic effects of a gasless procedure and insufflation with different gases were compared in rats. Methods: In all the experiments, Donryu rats were randomized to receive a gasless procedure; to receive insufflation with CO₂, helium, or air at 10 mmHg for 30 min, or to serve as control subjects without insufflation. In experiment 1, involving 60 rats, ascites hepatoma AH130 cells were inoculated intraperitoneally just before the procedures. The S-phase fraction of the intraperitoneal tumor cells was determined using a flow cytometry on day 7. In experiment 2, 60 rats injected intraperitoneally with latex particles received one of the procedures. At the end of the procedure, peritoneal macrophages were harvested to determine the number of phagocytosed particles. In experiment 3, 75 rats inoculated intraperitoneally with AH130 cells received one of the procedures for 5 consecutive days and were followed for survival analysis. Results: Experiment 1: The S-phase fraction was lower after insufflation with air or helium (p < 0.01) than with the anesthesia control condition. Insufflation with CO₂ showed a higher S-phase fraction than the gasless procedure or insufflation with air or helium ( p < 0.01). Experiment 2: The phagocytotic activity of peritoneal macrophages was increased by insufflation with helium and air, as compared with the control condition ( p < 0.01). Insufflation with CO₂ deteriorated the phagocytotic activity more than the gasless procedure ( p < 0.05) or insufflation with air or helium ( p < 0.001). Experiment 3: Insufflation with gases demonstrated shorter survival than the anesthesia control condition or the gasless procedure regardless of the gases used (p < 0.01). Conclusions: These results suggest that the choice of gases may affect the proliferation of tumor cells and the phagocytotic activity of peritoneal macrophages, insufflation itself may promote tumor spread regardless of the gases used, and the gasless procedure may be oncologically advantageous in this animal model.