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


CONCLUSIONS
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.
Kobayashi
Y
Y
Department of Anesthesia, Asahikawa City Hospital, 1-1-65 Kinsei-cho, Asahikawa 070-8610, Japan.
Seki
S
S
Ichimiya
T
T
Iwasaki
H
H
Namiki
A
A