[Continuous monitoring of end-tidal CO2-tension in non-intubated patients]

We describe and evaluate a method for continuously monitoring end-tidal CO2 (PETCO2) in non-intubated, spontaneously breathing patients. In 18 ASA I patients scheduled for minor surgery a 3.3 mm (10 CH) soft plastic catheter was preoperatively inserted through one nostril placing the tip at the level of the epiglottis. In the recovery room a capnograph was connected to the catheter for monitoring PETCO2. We found no significant differences between arterial carbon dioxide tension (PaCO2) and PETCO2 obtained by the catheter (0.2 +/- 2.2 mmHg) or obtained by a maximal expiration through a mouthpiece (-0.8 +/- 2.8 mmHg). We tested the possibility of mixing expired air with supplementary oxygen via the other nostril at a flowrate of 15 litres min-1, and found no significant difference in PETCO2 with or without flow (0.0 +/- 0.9 mmHg). Values are mean +/- SD. In conclusion we find that this method allows accurate monitoring of PETCO2 in non-intubated, spontaneously breathing patients even at supplementary oxygen flow-rates of up to 15 litres min-1.