Background and Objectives: Tracheal gas insufflation (TGI) consists in injecting gas in the trachea (usually oxygen). is used in patients with acute respiratory distress syndrome (ARDS) to reduce capnometry. In Anesthesiology, the reduction in capnometry can be useful, but there are no studies on the reduction in capnometry using TGI. The objective of this study was to evaluate the changes caused by TGI on capnometry in anesthetized patients., Methods: Eleven patients, ages 18 to 60 years, ASA I or II, without lung diseases were evaluated prospectively. After tracheal intubation, a TGI catheter was inserted 2 to 3 cm from the carina. Patients underwent volume-controlled ventilation. The volumetric capnography curve was recorded during 20 minutes and blood was drawn to determine the PaCO2. Twenty minutes after TGI was instituted, the capnograph curve was recorded and blood was drawn once more to measure PaCO2. The end-tidal partial pressure of CO2(P(ET)CO2) and PaCO2 were evaluated before and after TGI. The capnography curve was observed before and during TGI., Results: PaCO2 and P(ET)CO2 without TGI were: 33.48 +/- 6.81 and 36.91 +/- 6.54 mmHg (mean +/- standard deviation), respectively, and after TGI, 33.85 +/- 8.31 and 36.55 +/- 7.93 mmHg, respectively. Parameters were not statistically different before and after TGI, both for PaCO2 and P(ET)CO2 (p = 0.65 and 0.82). The capnography curve showed changes in alveolar air during expiration., Conclusions: The use of TGI did not result in a reduction in PaCO2 or P(ET)CO2 but it altered the morphology of the capnography curve.