Relationship between arterial and end-tidal carbon dioxide pressures during anesthesia using a laryngeal tube

Background: The Laryngeal TubeⓇ (LT), (VBM Medizintechnik, Sulz, Germany) is a relatively new supraglottic device for controlling the airway. Arterial carbon dioxide tension (PaCO2) can be estimated by monitoring the end-tidal tension of carbon dioxide (PETCO2). The relationship between PETCO2 and PaCO2 during controlled ventilation via the LT has not been reported. Methods: During general anesthesia, 45 patients were mechanically ventilated using an LT. PETCO2 and PaCO2 were measured once PETCO2 had reached a steady state. The LT was then removed and the trachea intubated using an endotracheal tube (ETT), and the identical ventilatory variables were resumed. Following stabilization, PETCO2 was again determined and PaCO2 estimated. Results: The mean PETCO2 and PaCO2 values were 4.43 ± 0.26 kPa and 4.67 ± 0.32 kPa, respectively, during LT ventilation, and 4.36 ± 0.23 kPa and 4.61 ± 0.26 kPa, respectively, during ETT ventilation. Analysis of differences between the PETCO2 and PaCO2 values using the Bland and Altman method revealed a bias ± precision of 0.24 ± 0.15 kPa for LT and 0.27 ± 0.15 kPa for ETT. The root mean square error was 0.28 for the LT and 0.30 for the ETT. Conclusion: This study suggests that for healthy adult patients mechanically ventilated via the LT, the PETCO2 value reflects the PaCO2 value as closely as when patients are ETT ventilated, allowing capnometry to be used to evaluate the adequacy of ventilation.restrictio