INTRODUCTION:
We have shown that the inflammation-attenuating effects of CO2-pneumoperitoneum during laparoscopy are not due to changes in systemic pH. However, acidification of peritoneal macrophages in an in vitro CO2 environment has been shown to reduce LPS-mediated cytokine release. We tested the hypothesis that the peritoneum is locally acidotic during abdominal insufflation with CO2- even when systemic pH is corrected.

METHODS:
Twenty rats were anesthetized with isoflurane and randomized into two groups: continued spontaneous ventilation (SV) or intubation and mechanical ventilation (MV). Femoral artery and vein catheters were inserted and a peritoneal pH probe was placed percutaneously behind the liver. All animals were then subjected to abdominal insufflation with CO2 at 4 mmHg for 30 min.

RESULTS:
Mean arterial pH among SV rats decreased significantly from baseline after 15 and 30 min of CO2-pneumo (7.329--7.210--7.191, p<0.05), while arterial pH among MV rats remained relatively constant (7.388--7.245--7.316, p=NS). In contrast, peritoneal pH dropped significantly from baseline and remained low for both groups during CO2 abdominal insufflation (SV 6.74--6.41--6.40, p<0.05; MV 6.94--6.45--6.45, p<0.05). Peritoneal pH returned to baseline levels in both groups within 15 min of desufflation.

CONCLUSIONS:
A significant local peritoneal acidosis occurs during CO2 laparoscopy which is independent of systemic pH. This finding provides additional evidence that peritoneal acidosis is central to the mechanism of CO2-mediated attenuation of the inflammatory response following laparoscopic surgery.