Relationship between end-tidal and arterial carbon dioxide partial pressure using a cuffed oropharyngeal airway and a tracheal tube.

We have compared the differences between end-tidal PE'CO2 and arterial PaCO2 carbon dioxide partial pressures during general anaesthesia using either a cuffed oropharyngeal airway (COPA) or a tracheal tube (TT) in spontaneously breathing adult patients. After induction of anaesthesia, a COPA was inserted in 20 patients who were allowed to breathe spontaneously. When steady state was reached, PE'CO2 and PaCO2 were recorded. The COPA was removed, the trachea intubated with a TT and spontaneous ventilation allowed to resume. After a stable PE'CO2 was reestablished, PaCO2 was measured again and PE'CO2 recorded. Mean difference between PaCO2 and PE'CO2 with the COPA was 0.72 (SD 0.45) kPa and with the TT 0.64 (0.40) kPa (ns; paired t test). Our results suggest that Pe'CO2 is a clinically acceptable indicator of PaCO2 in adults breathing spontaneously via a COPA.