Objective To evaluate the effectiveness and the accuracy of partial pressure of end-tidal carbon dioxide (PetCO₂) monitoring of the new nasopharyngeal airway in the application of ultrasound-guided nerve block anesthesia in orthopedic lower extremity surgery. Methods A total of 40 patients scheduled for orthopedic lower extremity surgery were included. Lumbar plexus and sciatic nerve block were conducted first followed by placement of a new nasopharyngeal airway under mild sedation. After connection with the oxygen tube, radial artery puncture was performed with monitored PetCO₂. Blood gas analysis was monitored, and the bispectral index(BIS) was maintained between 60-70 intraoperatively by continuous pumping small doses of propofol. Blood gas analysis and PetCO₂ were recorded at the placement of nasopharyngeal airway, at the beginning of the surgery, at 1 hour after the beginning of the surgery, and at 20 minutes before the end of surgery. GraphPad Prism 6.0 was employed for data analysis. Pearson correlation analysis and Bland-Altman consistency analysis were used to compare PetCO₂ measured by the new nasopharyngeal airway with PaCO₂ obtained in blood gas analysis. The change of intraoperative PaO₂ was also recorded to evaluate the effectiveness of the new nasopharyngeal airway. Intraoperative and postoperative nasopharyngeal and pulmonary complications were recorded. Results Operations were successful in all the patients. PetCO₂ monitored by nasopharyngeal airway at different time points(at the placement of nasopharyngeal airway, at the beginning of surgery, at 1 hour after the beginning of surgery, and at 20 min before the end of surgery) correlated with PaCO₂ with good consistence (r=0.918,0.906,0.824 and 0.875; all P＜0.05). Bland-Altman method comparison showed that only two difference points were outside the 95% agreement bound at the four time points, and the consistency was 95%. No patient had hyoxemia in the surgery or postoperative pulmonary complications.Conclusion The new nasopharyngeal airway can be used for nerve block anesthesia in orthopedic lower extremity surgery.