Supplementary oxygenation with the laryngeal mask airway: a comparison of four devices

The provision of supplementary oxygen via the laryngeal mask airway used in the recovery room is important for patient safety. Several devices have been described for this purpose, but these studies have not included an accurate measurement of the most clinically important variable, the end-tidal oxygen concentration. We constructed an artificial model of spontaneous ventilation to compare the efficacy and safety of four devices; a circuit filter, a Hudson mask, the 'T-bag' device and a T-piece. We combined the use of oximetry with a pneumotachograph to provide a continuous picture of the oxygen delivery characteristics of the devices at flow rates of 2, 4 and 8 l.min-1. The performances of the T-bag and the T-piece were superior to those of the filter and Hudson mask, with end-tidal oxygen concentrations of 46.1%, 45.8% and 35.4%, 34.8%, respectively, at 8 l.min-1. Single point assessments of oxygen delivery, such as peak inspired oxygen concentration, may overestimate the efficacy of test devices.