Image: The double mask can decrease exposure risk of inhaled anesthetic agents.  Image source courtesy of Anesthesia & Analgesia
The double mask can decrease exposure risk of inhaled anesthetic agents. Image source courtesy of Anesthesia & Analgesia

In operating rooms in the United States, due primarily to risk of adverse reproductive effects, there are limits set by the National Institute for Occupational Health and Safety for exposure to nitrous oxide (25 ppm) and potent inhalation agents (2 ppm). Limited exposure to anesthetic gases in hospitals is accomplished in large part via the use of an increased number of air exchanges. In a doctor’s office, however, increasing the number of air exchanges is usually not possible. A special type of face mask, known as a “double mask,” has been devised where a second large mask is mounted on top of the actual face mask and is connected to high flow suction. Since this mask has been approved for use in Canada, Dr. Matt Kurrek, MD, Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada, and co-authors studied patients in nine freestanding dental offices where anesthetic waste gas levels were compared before and after use of the double mask. Their findings are published in the article “The Effect of the Double Mask on Anesthetic Waste Gas Levels During Pediatric Mask Inductions in Dental Offices.”

The authors used nitrous oxide and sevoflurane for anesthesia induction; nitrous oxide and a volatile anesthetic were used for anesthesia maintenance. Before use of the double mask, the median nitrous oxide level was 40 ppm and the median sevoflurane level was 4.6 ppm. After the double mask was used, nitrous oxide levels fell to 3 ppm and none of the offices had levels greater than 25; sevoflurane median values were 0 ppm and no office had values greater than 2 ppm.

There is no waste anesthetic gas level when total intravenous anesthesia is used. For children, an IV may be more easily inserted once the child has been anesthetized, however.

Though this mask is not yet available in the United States, the overall concept described, namely limits for safety of different inhaled agents used in operating rooms, is a question that is frequently asked of trainees.