Associations Between Fresh Gas Flow and Duration of Anesthetic on the Maximum Potential Benefit of Anesthetic Gas Capture in Operating Rooms and in Postanesthesia Care Units to Capture Waste Anesthetic Gas

Abstract

BACKGROUND: Sevoflurane and desflurane are halogenated hydrocarbons with global warming potential. We examined the maximum potential benefit assuming 100% efficiency of waste gas capture technology used in operating rooms and recovery locations. METHODS: We performed computer simulations of adult patients using the default settings of the Gas Man software program, including the desflurane vaporizer setting of 9% and the sevoflurane vaporizer setting of 3.7%. We performed 21 simulations with desflurane and 21 simulations with sevoflurane, the count of 21 = 1 simulation with 0-hour maintenance + (1, 2, 3, 4, or 5 hours of maintenance) × (0.5, 1, 2, or 4 L per minute fresh gas flow during maintenance). RESULTS: (1) A completely efficient gas capture system could recover a substantive amount of agent even when the case is managed with low flows. All simulations had at least 22 mL agent recovered per case, considerably greater than the 12 mL that we considered the minimum volume of economic and environmental importance. (2) All 42 simulations had at least 73% recovery of the total agent administered, considerably greater than the median 52% recovery measured during an experimental study with one gas capture technology and desflurane. (3) The maximum percentage desflurane (or sevoflurane) that could be captured decreased substantively with progressively longer duration anesthetics for low-flow anesthetics but not for higher-flow anesthetics. However, for all 8 combinations of drug and liters per minute simulated, there was a substantively greater recovery in milliliters of agent for longer duration anesthetics. In other words, if gas capture could be near perfectly efficient, it would have greater utility per case for longer duration anesthetics. (4) Even using a 100% efficient gas capture process, at most 6 mL liquid desflurane or 3 mL sevoflurane per case would be exhaled during the patient’s stay in the postanesthesia care unit. Therefore, the volume of agent exhaled during the first 1 hour postoperatively is not a substantial amount from an environmental and economic perspective to warrant consideration of agent capture by having all these patients in the postanesthesia care unit, or equivalent locations, using the specialized anesthetic gas scavenging masks with access to the hospital scavenging system at each bed. CONCLUSIONS: Simulations with Gas Man show a strong rationale based on agent uptake and distribution for using volatile anesthetic agent capture in operating rooms if the technology can be highly efficient at volatile agent recovery.