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Abdominal Insufflation with CO2 Causes Peritoneal Acidosis Independent of Systemic pH
Eric J. Hanly, Joseph M. Fuentes, Alexander R. Aurora, Samuel P. Shih, Michael R. Marohn, Antonio De Maio, Mark A. Talamini, Johns Hopkins University, Baltimore, MD

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.


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