Nitrous oxide in waste anesthetic gases with different fresh gas flow: a case-based pilot observation and a practical thought on scavenging

Use of nitrous oxide (N(2)O) as an anaesthetic gas has been on contradicting views for various reasons; operating room (OR) pollution and occupational exposure is one of those controversies. The present pilot experiment was planned to analyze the anaesthesia gas waste at the machine end of scavenging outlet and calculate the probable portion of N(2)O in the OR air, which is likely to help us in informed decision making. Anaesthesia gas waste was sampled at the machine end of scavenging outlet and was connected directly and analyzed using a gas analyzer attached to Mindray A7 anaesthesia workstation. An assembly of L connector, sampling line, corrugated tube and endotracheal tube were used to perform the procedure. The measurements were taken at 600, 1200 and 1800 mL/minutes of fresh gas flow (FGF). A total of 15 paired readings from five general anaesthesia cases were taken. The N(2)O percentage in the anaesthesia waste gases with a FGF of 600, 1200 and 1800 mL was 3.4 ± 0.54, 8.2 ± 0.83 and 14.0 ± 0.70, respectively. On calculation, the likely concentration of N(2)O in OR with FGF of 600 mL/min is 0.576 ppm, which will lead to the time weighted average 4.6 ppm exposure per day in modular OR. Reducing FGF to 600 mL/min reduces the N(2)O concentration in OR by 75% as compared to the FGF of 1800 mL/min. The time weighted average exposure to N(2)O is far below the permissible limit in modular OR.