Cuffed oropharyngeal airway and capnometry: comparison of end-tidal and arterial carbon dioxide pressures

Abstract

Purpose. The aim of this study was to investigate the reliability of end-tidal CO₂ tension (PetCO₂) as a predictor of PaCO₂ during anesthesia in patients breathing spontaneously via a cuffed oropharyngeal airway (COPA).

Methods. Twenty adult patients scheduled for minor sur-gery 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. PaCO₂ and PetCO₂ were simultaneously measured when a steady state of anesthesia was reached.

Results. PaCO₂ (48.8 ± 5.4 mmHg, range 36.2–58.0 mmHg) was higher than PetCO₂ (43.1 ± 4.2 mmHg, range 32–51 mmHg) in all patients. The difference between end-tidal and arterial CO₂ tension was 5.7 ± 3.2 mmHg (range 0.5–13.0 mmHg), and was significantly correlated with PaCO₂ (P < 0.01).

Conclusion. The results of this study suggest that PetCO₂ in anesthetized patients breathing spontaneously through a COPA is sometimes unreliable as an indicator of PaCO₂ level, and there is some possibility of unexpected hypercapnia.