PubMed · 6575304
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J V Hay. 1983-07-27. Ethical considerations.. https://pubmed.ncbi.nlm.nih.gov/6575304/
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Thirty-two females, ASA class I, scheduled for termination of pregnancy before the 13th week participated in the study. After induction of anaesthesia, a soft plastic catheter was inserted in the oropharynx and the patients were postoperatively monitored with a capnograph, which sampled in- and expired air from the catheter. In a randomized cross-over design the patients received oxygen therapy by the Hudson face-mask and a nasal cannula. Humidified and heated oxygen was given in both cases, using a flow of 15 litres per minute. The nasal cannula resulted in a significantly higher expired end-tidal O2-fraction (FETO2) compared to the Hudson mask. During the nasal cannula period the respiratory rate was significantly lower than during the face mask period. The end-tidal CO2 pressure (PETCO2) remained constant.
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.