Correlation of the End-Tidal PCO2 during Laparoscopic Surgery with the pH of the Gastric Juice

BACKGROUND AND OBJECTIVES During laparoscopy, the increase of the carbon dioxide tension may increase the synthesis of hydrochloric acid in the parietal cells of the stomach; the source of the secreted hydrogen ions is carbonic acid derived from the hydration of carbon dioxide. The present report tests this hypothesis by correlating the changes of end-tidal PCO2 (ETCO2) with the pH of the gastric juice in patients undergoing laparoscopic cholecystectomy. METHODS 40 adult patients were investigated: 20 controls, and 20 patients receiving 100 mg nizatidine intravenously, prior to surgery. In both groups, the ETCO2 was measured by capnography and the pH of the gastric juice was monitored before carbon dioxide insufflation and at the end of laparoscopy prior to carbon dioxide deflation. RESULTS In the control group, the ETCO2 increased following carbon dioxide insufflation from a mean basal value of 30.2 (standard deviation [SD] 4.6) mm Hg to 41.1 (SD 9.5) mm Hg, while the mean pH of the gastric juice decreased significantly from 1.9 (SD 0.4) to 1.27 (SD 0.43). There was a significant negative correlation between the ETCO2 and pH of the gastric juice (r = -0.4). In the Nizatidine group, the ETCO2 also increased following carbon dioxide insufflation from a mean basal value of 30.9 (SD 3.0) mm Hg to 39.4 (SD 5.3) mm Hg. However, in contrast with the control group, the mean pH of the gastric juice did not decrease, but paradoxically increased from 1.68 (SD 0.36) to 3.6 (SD 1.02). CONCLUSIONS During laparoscopy, the pH of the gastric juice is significantly decreased. This decrease is inversely related to the increase of ETCO2. The preoperative administration of the selective H2-blocker nizatidine can prevent the increase in gastric acidity and can result in a paradoxical increase of pH of the gastric juice.