Nitrous oxide is a potent greenhouse gas that persists in the atmosphere for over a century, with a global warming potential 273 times that of the reference unit carbon dioxide (Anesth Analg 2012;114:1081-5). Further, nitrous oxide is the most dominant ozone-depleting gas, increasing skin cancer risks to humans and other animals from excessive ultraviolet light exposure (Science 2009;326:123-5; Br J Anaesth 2020;125:680-92). While contributions to global atmospheric emissions from health care are difficult to discern from natural sources (such as volcanic eruptions), worldwide anesthetic use has been estimated to contribute between 1%-3% of the global nitrous oxide footprint (Br J Anaesth 2020;125:680-92). At the level of the health care facility, waste anesthetic gases can account for 5% of an acute care organization’s greenhouse gas emissions, and half or more of this can come from nitrous oxide alone (Br J Anaesth 2021;126:e193-5; asamonitor.pub/3Rgrp0n). Fortunately, most anesthetic pollution from health care facilities is avoidable.
Of the four main inhaled anesthetics, the volatile agents desflurane, sevoflurane, and isoflurane require a vaporizer device on an anesthesia machine, while the compressed gas nitrous oxide is routinely piped through facility walls from large central tanks. These large, high-pressure tanks (sometimes interconnected in series) are connected through manifolds to the central pipes and reach the point of care for uninterrupted on-demand use. Significant leaks routinely occur at the manifold connections and are worse with cryogenically condensed tanks than with compressed tanks, owing to greater mass. The recommendation is to abandon existing central pipe systems, avoid installing them in new construction, and instead substitute small, portable e-cylinder tanks for direct use at the point of care that remain closed between cases.
While switching to portable tanks seems simple, several barriers exist, including lack of facility and perioperative leadership knowledge about this issue, concerns around increased storage space, additional staffing requirements, and retrofitting costs. These concerns are surmountable, however.
Staff buy-in requires baseline and progress performance measurements (Anaesthesia 2022;77:1023-9). This begins most simply with obtaining procurement nitrous oxide records from the medical gas department, including quantities (in total liters) and costs per facility. Next, clinical utilization should be assessed through extracting electronic health record (EHR) data, including summaries of fresh gas flow rates (liters per minute) and duration of use. (No protected health information is required.) Room location of nitrous oxide use should also be assessed to identify areas of high utilization. Clinical staff utilization can also be assessed in this way. Procurement data should be compared against clinical utilization records to quantify facility-level-relative and absolute losses, costs, and emissions. Hospital leaders in possession of this data should be inclined to abandon central piping; however, further considerations are necessary.
Substituting portable e-cylinders will require evaluation of any additional space and support staff needs. This can be accomplished by dividing total liters of nitrous oxide used (liters/min x total minutes) by the liters per e-cylinder (680) to estimate the number of portable tanks required in any given time frame and location. These estimates are essential to ensure adequate code-compliant storage space and handling staff. Surprisingly, results may demonstrate that no changes are required to existing space or staff.
The biggest obstacle managers may face with abandoning central piping is if anesthesia machines require retrofitting to support portable nitrous oxide e-cylinders. Vendor quotes can range between $3,000-$5,000 for modifications per machine, which can be cost-prohibitive, even when accounting for 95% savings on nitrous oxide procurement, given its low cost. Solutions include targeted retrofitting; applying aforementioned EHR data to identify locations of high utilization, e.g., pediatric ORs; avoiding central nitrous oxide piping in new construction and applying averted costs; selecting nitrous oxide fitting options when performing anesthesia machine upgrades (typically every 10-15 years); and getting clinical staff buy-in to abandon nitrous oxide from the formulary altogether.
ASA recently approved a statement declaring low-flow sevoflurane as safe, below the lower limits noted in the FDA package insert (asamonitor.pub/3GzEEnM; Anesth Analg 2023;136:327-37; ASA Monitor 2023;87:e4-5). While specific to sevoflurane, this guidance can reassure clinicians overall, and also because sevoflurane is frequently used in combination with nitrous oxide. In addition, the Anesthesia Patient Safety Foundation now offers a free online low-flow simulator course, which can be especially helpful for trainees (asamonitor.pub/46Sul94). Importantly, clinical staff may elect to remove nitrous oxide from their hospital formularies altogether; even some pediatric groups are suggesting it is unnecessary (Paediatr Anaesth October 2023). If this commitment is too large for a department, ensuring availability of portable e-cylinders in select locations may be culturally acceptable for clinicians and can also satisfy leadership concerns around retrofitting cost constraints.
The climate crisis is rapidly accelerating and threatening human and planetary health (Lancet 2022;400:1619-54). The U.S. health care sector contributes approximately 8.5% of total national greenhouse gas emissions and 1.25% of total global greenhouse gas emissions (Lancet 2022;400:1619-54; Health Aff 2020;39:2071-9). Recognizing both feasibility and impact, the Agency for Healthcare Research and Quality’s Primer on Measures and Actions for Healthcare Organizations to Mitigate Climate Change and The Joint Commission’s Sustainable Healthcare Certification program support inhaled anesthetic emission reductions (asamonitor.pub/41sSgLv; asamonitor.pub/48EwruI). Electively abandoning central nitrous oxide piping presents an important opportunity to mitigate this pollution.