Environmental and Occupational Considerations of Anesthesia: A Narrative Review and Update

Abstract

With an estimated worldwide volume of 266 million surgeries in 2015, the call for general inhalation anesthesia is considerable. However, widely used volatile anesthetics such as N2O and the highly fluorinated gases sevoflurane, desflurane, and isoflurane are greenhouse gases, ozone-depleting agents, or both. Because these agents undergo minimal metabolism in the body during clinical use and are primarily (≥95%) eliminated unchanged via exhalation, waste anesthetic gases (WAGs) in operating rooms and postanesthesia care units can pose a challenge for overall elimination and occupational exposure. The chemical properties and global warming impacts of these gases vary, with atmospheric lifetimes of 1-5 years for sevoflurane, 3-6 years for isoflurane, 9-21 years for desflurane, and 114 years for N2O. Additionally, the use of N2O as a carrier gas for the inhalation anesthetics and as a supplement to intravenous (IV) anesthetics further contributes to these impacts. At the same time, unscavenged WAGs can result in chronic occupational exposure of health care workers to potential associated adverse health effects. Few adverse effects associated with WAGs have been documented, however, when workplace exposure limits are implemented. Specific measures that can help reduce occupational exposure and the environmental impact of inhaled anesthetics include efficient ventilation and scavenging systems, regular monitoring of airborne concentrations of waste gases to remain below recommended limits, ensuring that anesthesia equipment is well maintained, avoiding desflurane and N2O if possible, and minimizing fresh gas flow rates (eg, use of low-flow anesthesia). One alternative to volatile anesthetics may be total intravenous anesthesia (TIVA). While TIVA is not associated with the risks of occupational exposure or atmospheric pollution that are inherent to volatile anesthetic gases, clinical considerations should be weighed in the choice of agent. Appropriate procedures for the disposal of IV anesthetics must be followed to minimize any potential for negative environmental effects. Overall, although their contributions are relatively low compared with those of other human-produced substances, inhaled anesthetics are intrinsically potent greenhouse gases and pose a risk to operating-room personnel if not properly managed and scavenged. Factors to reduce waste and minimize the future impact of these substances should be considered.

Figure 1.

The total annual US GHG emission in 2012 was 6.2 gigatons of CO₂ equivalent, of which 6.8% comprised N₂O (4.3%) and fluorinated gases (3%; hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride). The contributions of inhaled anesthetics (N₂O, desflurane, isoflurane, and sevoflurane) to US GHG emissions for 2011−2013 were estimated to be 5.6 million tons of CO₂ equivalent (excluding dental, laboratory, and veterinary medicine),^, comprising approximately 1% of GHG emissions from the US health care sector and approximately 0.1% of total US GHG emissions.^, GHG indicates greenhouse gas.

Figure 2.

Structure and life-cycle GHG emissions of flurorinated volatile anesthetics. A, Structural formulas of the most frequently used fluorinated volatile anesthetics.^– B, Life-cycle GHG emissions of anesthetics, including waste anesthetic gas emissions of halogenated drugs and N₂O. Life-cycle GHG emissions shown in (B) are based on a functional unit of 1 MAC or MAC-equivalent for propofol, for maintenance anesthesia for an average 70-kg adult patient for 1 h (1 MAC-h). Panel B and 1 MAC-h definition have been reprinted from Sherman J, et al. by permission of Wolters Kluwer Health on behalf of the International Anesthesia Research Society. GHG indicates greenhouse gas; MAC, minimum alveolar concentration.

Figure 3.

Global warming impact of inhaled anesthetics in perspective.^{, a}Assumes a US automobile average for CO₂ emissions of 398 g/mile. ^bDetermining the precise climate impact of worldwide anesthetic procedures is complicated because of limited available data on usage or production of anesthetic agents.