BACKGROUND: The administration of 100% oxygen at the end of general anesthesia before tracheal extubation has been shown to worsen postanesthetic pulmonary gas exchange. Because the laryngeal mask airway (LMA) and the endotracheal tube (ETT) are very different, it remains uncertain whether emergence on oxygen has the same results on lung function as ETT. Therefore, the aim of this study was to evaluate whether the use of 100% oxygen before LMA removal worsens gas exchange after inhalation or total intravenous general anesthesia.

METHODS: Eighty ASA physical status I-II patients scheduled for elective surgery of the extremities were randomly assigned to receive either sevoflurane or propofol during general anesthesia with LMA. At the end of surgery, patients were randomized to an inspiratory fraction of oxygen of 0.3 in sevoflurane (n = 20), of 0.3 propofol (n = 20) or of 1.0 in sevoflurane (n = 20) or of 1.0 in propofol (n = 20) during emergence from anesthesia and LMA removal. Postoperative blood gas measurements were taken immediately and 60 min after arrival in the recovery room.

RESULTS: No significant differences in PaO₂ (propofol groups: 87.5 ± 14.4 vs 88.5 ± 10.5 mmHg, sevoflurane groups: 86.7 ± 11.3 vs 90.7 ± 9.9 mmHg) or alveolar - arterial oxygen tension difference (AaDO₂) were found between the two groups at 30 min after LMA removal (propofol groups: 12.0 ± 12.4 vs 10.3 ± 8.3 mmHg, sevoflurane groups: 8.6 ± 7.1 vs 7.1 ± 9.4 mmHg). No differences were observed between the sevoflurane and propofol groups when F_IO₂ levels were similar.

CONCLUSIONS: Breathing 100% oxygen during emergence from general anesthesia does not worsen postanesthetic pulmonary gas exchange when an LMA is used.