Effects of Paratracheal Compression and Cricoid Compression on LMA ProSeal Placement

The time required for placement will be defined as the time from receipt of the LMA ProSeal to detection of the square waveform on capnography and will be calculated by summing the time taken for each attempt.

Insertion of the LMA ProSeal will be assessed on a 4-point scale (1, no resistance; 2, moderate resistance; 3, severe resistance; and 4, impossible to insert the LMA ProSeal).

It will be evaluated with a fibreoptic bronchoscope placed inside the tube section of the the LMA ProSeal. Accuracy will be recorded on a five-point scale (1, only the glottis is observed; 2, the posterior surface of the epiglottis and the glottis are observed; 3, the anterior part or tip of the epiglottis and >50% of the glottis are observed; 4, the folded down epiglottis and <50% of the glottis are observed; 5, the glottis is completely hidden by the folded down epiglottis)

Tidal volume and peak inspiratory pressure with or without manoeuvre will be recorded with the same ventilator settings determined for all patients.

Oropharyngeal leak pressure will be assessed by closing the expiratory valve of the circle system to 40 cmH2o, with a fresh gas flow of 3 L/min and noting the airway pressure when equilibrium is reached or an audible air leak occurs.