Supplementary oxygen and the laryngeal mask airway : Evaluation of a heat-and-moisture exchanger

Heat-and-moisture exchangers (HMEs) are routinely used in anaesthesia for the humidification and warming of inspired gases. The use of the Laryngeal Mask Airway (LMA) is widespread, and many anaesthetists choose to leave it in situ until the patient regains consciousness. In this study, we have investigated the effectiveness of an HME as a means of administering supplemental oxygen via LMA in the immediate postoperative period. Oxygen was administered at varying flow rates via the gas sampling port of the HME and the oxygen delivery recorded, using end-tidal oxygraphy as a measure of alveolar PO2. At an oxygen flow rate of 4 l.min-1, the HME provided a mean end-tidal oxygen concentration of 36.2% (+/- 6.2), which compares favourably to other previously described devices. The HME thus represents a convenient, effective and economical means of oxygen supplementation via the LMA.