The use of breathing system filters as oxygen-delivery devices

A breathing system filter can remain connected to a laryngeal mask airway during recovery from anaesthesia. The Luer-lock monitoring port on the filter could be used for the delivery of supplementary oxygen. The efficacy of this technique was assessed in vitro by comparing the performance of two filters with four other devices, including a T-piece with a 40% oxygen injector. The minimum inspired oxygen fraction and pressure drop were measured over a range of ventilatory conditions and oxygen flows. The minimum inspired oxygen fraction measured with the remaining devices was greater than with the T-piece at an oxygen flow of 10 l.min-1. The pressure drop was greater with the breathing system filters than with the T-piece. A potential advantage in using filters is that no additional equipment is required. However, if using the filters as oxygen supplementation devices, there is only one port open to the atmosphere in the system and inadvertent obstruction of this port could cause barotrauma. It must be remembered that the nonstandard use of such equipment contravenes the recently introduced Medical Device Directive regulations.