Purpose: The aim of this study was to investigate the reliability of end-tidal CO(2) tension (PetCO(2)) as a predictor of PaCO(2) during anesthesia in patients breathing spontaneously via a cuffed oropharyngeal airway (COPA).
Methods: Twenty adult patients scheduled for minor surgery were included in this study. After propofol injection, an appropriate size of COPA was inserted. Anesthesia was maintained with 60% nitrous oxide in oxygen (total flow rate of 5 l.min(-1)) supplemented with propofol infusion. The patients were allowed to breathe spontaneously throughout the procedure. PaCO(2) and PetCO(2) were simultaneously measured when a steady state of anesthesia was reached.
Results: PaCO(2) (48.8 +/- 5.4 mmHg, range 36.2-58.0 mmHg) was higher than PetCO(2) (43.1 +/- 4.2 mmHg, range 32-51 mmHg) in all patients. The difference between end-tidal and arterial CO(2) tension was 5.7 +/- 3.2 mmHg (range 0.5-13.0 mmHg), and was significantly correlated with PaCO(2) ( P < 0.01).
Conclusion: The results of this study suggest that PetCO(2) in anesthetized patients breathing spontaneously through a COPA is sometimes unreliable as an indicator of PaCO(2) level, and there is some possibility of unexpected hypercapnia.