Effect of pressure and gas type on intraabdominal, subcutaneous, and blood pH in laparoscopy.

BACKGROUND: According to the literature, the number of port-site metastases in laparoscopic surgery varies considerably depending on the type of gas used for the pneumoperitoneum. In order to investigate this observation we studied the changes in blood, subcutaneous, and intra-abdominal pH during laparoscopy with helium, CO(2) and room air in a rat model. In addition, we looked at the influence of intra-abdominal pressure and duration of pneumoperitoneum 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 the results compared to those measured by tonometry. Blood samples were taken from a catheter in the carotid artery. The intra-abdominal pressure was 0, 3, 6, 9 mm Hg for 30 min in each case. We investigated the effect of pneumoperitoneum with CO(2), helium and air in randomized groups of 5 rats. In an additional series the pressure was held constant at 3 mm Hg and the pH was measured every 30 min. RESULTS: Due to the different absorption capacity of the peritoneum, laparoscopy with CO(2) 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. Other, less absorbable gases induce smaller changes of blood and subcutaneous pH (only 10% of CO(2)). In a variance analysis the p value is less than 0.001. The influence of duration of laparoscopy (30 min vs. 90 min) on the subcutaneous pH is less compared to the influence of intra-abdominal pressure (0, 3, 6, 9 mm Hg). CONCLUSIONS: Depending on the type of gas (CO(2), air, helium) used for laparoscopy blood, subcutaneous and intra-abdominal pH are influenced differently. Because lower pH is known to impair local defense mechanisms, these results may be one explanation for the higher incidence of port-site metastasis in laparoscopy with CO(2) than with other gases, as reported in the literature.