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 (O2 group) or 33% oxygen in nitrous oxide (O2-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 O2-N2O group than the O2 group, other than at time zero (all: P<0.0001). CP increased every 5 min in the O2-N2O group (all: P<0.0001), but not in the O2 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 FP for any patient.


CONCLUSIONS
We conclude that OLP and FP are stable for the LMA during anaesthesia lasting 30 min with or without nitrous oxide.
Brimacombe
J
J
Department of Anaesthesia and Intensive Care, University of Queensland, Cairns Base Hospital, Australia. 100236,2343@compuserve.com
Keller
C
C
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005336:Fiber Optic Technology; D006801:Humans; D017214:Laryngeal Masks; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000008:administration & dosage*; D010100:Oxygen / Q000008:administration & dosage / Q000494:pharmacology*; D011312:Pressure
D009609:Nitrous Oxide; D010100:Oxygen