The effect of increase in end-tidal carbon dioxide on lower esophageal sphincter tone.

The lower esophageal sphincter is composed of smooth muscles and is the main barrier against regurgitation during anesthesia. As smooth muscles are usually sensitive to CO2, we investigated the response of lower esophageal sphincter pressure to varying concentrations of CO2 in six anesthetized pigs using a manometric method. CO2 was increased by increasing the dead space at the Y piece of the ventilator. Basal values for ETCO2 were 35 +/- 2 mm Hg, reaching 62 +/- 1 mm Hg at the end of the study (P < 0.03). In response to the increase in ETCO2, no change in lower esophageal sphincter pressure was noted (12 +/- 3 mm Hg vs 13 +/- 4 mm Hg). These findings indicate that the lower esophageal sphincter is not affected by CO2 in the range usually encountered in clinical practice.