Effect of pressure and gas type on intraabdominal, subcutaneous, and bloodpH in laparoscopy

Background: According to the literature, the number of port-site metastases in laparoscopic surgery varies considerably depending on the type of gas u sed for the pneumoperitoneum. In order to investigate this observation we s tudied the changes in blood, subcutaneous, and intra-abdominal pH during la paroscopy with helium, CO2 and room air in a rat model. In addition, we loo ked at the influence of intraabdominal pressure and duration of pneumoperit oneum on the pH during the laparoscopy. Methods: pH was measured by tonometry, intra-abdominally and subcutaneously . A pH electrode was additionally placed into the subcutaneous tissue and t he results compared to those measured by tonometry. Blood samples were take n from a catheter in the carotid artery. The intraabdominal pressure was 0, 3, 6, 9 mmHg for 30 min in each case. We investigated the effect of pneumo peritoneum with CO2, helium and air in randomized groups of 5 rats. In an a dditional series the pressure was held constant at 3 mmHg and the pH was me asured every 30 min. Results: Due to the different absorption capacity of the peritoneum, laparo scopy with CO2 decreases the subcutaneous pH from 7.35 to 6.81. Blood pH is reduced from 7.37 to 7.17 and the intra-abdominal pH from 7.35 to 6.24. Ot her, less absorbable gases induce smaller changes of blood and subcutaneous pH (only 10% of CO2). In a variance analysis the p value is less than 0.00 1. The influence of duration of laparoscopy (30 min vs 90 min) on the subcu taneous pH is less compared to the influence of intra-abdominal pressure (0 , 3, 6, 9 mmHg). Conclusions: Depending on the type of gas (CO2, air, helium) used for lapar oscopy blood, subcutaneous and intraabdominal pH are influenced differently . Because lower pH is known to impair local defense mechanisms, these resul ts may be one explanation for the higher incidence of port-site metastasis in laparoscopy with CO2 than with other gases, as reported in the Literatur e.