Does efficacy of seal and fibreoptic view change during anaesthesia with the laryngeal mask airway: A comparison of oxygen and oxygen-nitrous oxide gas mixtures

Background: We test the hypothesis that oropharyngeal leak pressure (OLP) and fibreoptic position (FP) are stable for the laryngeal mask airway (LMA) during anaesthesia with and without nitrous oxide. Methods: Forty paralysed anaesthetised patients (ASA 1-2, aged 18-80) were randomly allocated to receive 100% oxygen (O-2 group) or 33% oxygen in nitrous oxide (O-2-N2O group) for maintenance. In vivo intracuff pressure (CP) using a size 5 LMA was adjusted to 60 cm H2O. OLP, FP and CP were measured every 5 min for 30 min. Results: CP was higher in the O-2-N2O group than the O-2 group, other than at time zero (all: P<0.0001). CP increased every 5 min in the O-2-N2O group (all: P<0.0001), but not in the O-2 group. There were no differences in OLP and FP between groups at any time. There were no significant changes in OLP or FP with time within each group. There were no changes in OLP greater than 1.5 cm H2O and no change in Fr for any patient. Conclusion: We conclude that OLP and FP are stable for the LMA during anaesthesia lasting 30 min with or without nitrous oxide.