[The double mask]

While the consequences of occupational exposure to anesthetic gases and volatile agents on morbidity in operating room staff are controversial (survey in Swiss investigations show a distinct correlation with subjective complaints, e.g. tiredness and headache on the day of exposure (Table 1). In Sweden, rigorous control of occupational exposure to anesthetic gases has prompted development of various scavenging systems, among which the double mask (Fig. 1) is the latest and most advanced. During mask anesthesia, escaping anesthetic gases are evacuated at the point of leakage via a thin slot between a flexible silicone inner mask and a rigid plastic outer mask. A small plate in the mask produces turbulence in the otherwise laminar flow of anesthetic gases, thus reducing the speed of gas leakage. A silicone chamber is mounted on the mask and connected to a fan, requiring a flow of 35 m3/h for optimal function. This chamber does, however, also associate the system with two practical problems: the system with its evacuation tube is heavier to hold than conventional masks, and it is associated with increased dead-space that is only partly minimized by a modification of the Y-connector. While the handling is largely a matter of routine and the weight of the system is minimized when the evacuation tube is arranged to draw slightly upward, the increased dead space may reduce the practicality of the double mask in infants.