Anesthesia and the Environment

By Angela Herring, science writer for Northeastern University on June 13, 2013

Screen Shot 2013-06-12 at 5.28.06 PMA look at the environmental impact of anesthetic gases.

The potential health impacts of climate change are far reaching. Cardiovascular disease, heat-related asthma, and malnutrition due to compromised food security are just a few of the associated risks. The health-care system in which patients are eventually treated is responsible for eight percent of the nation’s greenhouse gas emissions. According to Yale University School of Medicine assistant professor of anesthesiology and environmental compliance Jodi Sherman and Northeastern University’s civil and environmental engineering assistant professor Matthew Eckelman, this all raises the interesting question of how the health-care industry itself is affecting our health through direct and indirect changes in our environment.

Sherman and Eckelman look at the life cycle of various products and processes—from production to destruction—to determine their overall environmental impact on a systems level. In a paper presented in the journal Anesthesia & Analgesia, Sherman and Eckelman performed life-cycle assessments of the major anesthetic gases used in the health care industry: nitrous oxide, desflurane, isoflurane, and sevoflurane, as well as a liquid anesthetic alternative, propofol.

“Any life-cycle assessment,” Eckelman says, “is a series of tradeoffs among different environmental impacts.” The health care system is designed to reduce human mortality and morbidity, but it is also important to understand the indirect or unintended effect­­s that health care has on the environment and public health. “The health care sector is increasingly concerned with sustainability issues,” he says.

The paper’s results show the relative environmental profile of each anesthetic alternative, and the important conclusion that the combined environmental impact of production, transportation, waste disposal, and other life-cycle events pales in comparison to the impact of the anesthetic gases alone.

“Anesthetic gases like nitrous oxide and the three halogenated ethers are greenhouse gases themselves,” says Eckelman, “and they’re quite potent.” Desflurane, for example, has a 100-year global warming potential more than 2,500 times that of carbon dioxide, he says.

Only small amounts of the gases are actually metabolized by the body. “The rest are usually vented out of the top of the hospital.” In addition to the anesthetic itself, these agents require a carrier gas, which can be oxygen combined with either air or nitrous oxide, says Eckelman. In cases where nitrous oxide is used, a large portion of the impact comes from emissions of the carrier gases.

Based on the research results, which put desflurane at the top of the list in terms of life-cycle greenhouse gas emissions, Dr. Sherman and her team made a series of recommendations for both doctors and hospitals. Within medical and cost considerations, they suggest doctors should avoid desflurane where possible; use oxygen as a carrier gas instead of nitrous oxide; minimize fresh gas flow rates; and employ IV anesthetic alternatives in applicable cases—propofol’s environmental impacts are negligible compared to the inhaled anesthetics.

The paper, which links health and sustainability, is part of a general international effort to bring life-cycle assessment to bear on various aspects of health care practice.

Desflurane removed from Yale-New Haven Hospital formulary based on climate impacts

Yale-New Haven Hospital recently removed Desflurane from its formulary, based largely on the environmental impact findings of Dr. Sherman and Dr. Eckelman. “In addition to its greenhouse gas impacts, Desflurane is also the most expensive drug in its class. Its clinical properties can be achieved with other drugs that have a much lower environmental footprint, and therefore its use can no longer be justified,” says Dr. Sherman. This is the first time that a pharmaceutical drug has ever been removed from clinical use based on climate impacts.

Life Cycle Greenhouse Gas Emissions of Anesthetic Drugs

By Jodi Sherman MD, Cathy Le, Vanessa Lamers and Matthew Eckelman PhD

When mitigating anesthetic gases, there are practical environmental impact strategies. Desflurane and N2O should be restricted to cases where they may reduce morbidity and mortality over alternative drugs. Clinicians should avoid unnecessary high fresh gas flow rates for all inhaled drugs. Although reducing fresh gas flow rates increases the requirement for CO2 absorbent and its concomitant footprint, this is unlikely to offset the benefits of reducing volatile drug and N2O use. Charcoal absorbers may be placed within the anesthesia circuit to capture volatile waste anesthetic gas.

Unfortunately, charcoal does not permanently remove the volatile drug. Volatile anesthetics diffuse into the atmosphere from charcoal absorbers in a matter of days, so they do not prevent emissions. Inhalation anesthetics are not generally included in climate change mitigation strategies because they are deemed “medically necessary.” Current Occupational Safety and Health Administration and Joint Commission regulatory language revolve around protection of worker safety through methods such as prevention of excessive exposure from handling, checking machines for leaks, and fire prevention. The American Society of Anesthesiologists-approved guidelines for waste anesthetic gas management recommend “discharging safely to the outside atmosphere.” There is currently no waste anesthetic gas policy limiting discharge of anesthetic gases into the atmosphere.

Technologies on the near horizon include photochemical air purification. This approach can theoretically destroy all waste anesthetic gases. Alternatively, current volatile waste anesthesia gas capturing systems can reclaim volatile gases for reuse rather than discharge waste into the atmosphere. The Dynamic Gas Scavenging System designed at Vanderbilt University is a cryogenic condensing system built into the exhaust system of multiple operating rooms. This system is activated only when the patient exhales. Because the vacuum pump is only intermittently active, the system has minimal impact on heating, ventilation, and air conditioning energy usage. Deltasorb is an alternative technology consisting of a canister that snaps into existing scavenging circuits. It uses a sieve-like filtering matrix that adsorbs volatile anesthetic gas. The canisters are returned to the vendor where the captured anesthetics can be extracted, liquefied, and processed into medical grade anesthetics (Blue-Zone Technology, Toronto, Canada). The Food and Drug Administration is presently considering approval for reprocessed volatile drugs, which may also find use in veterinary medicine. Propofol has the least overall impact on GHG emissions, even assuming a 50 percent wastage rate, disposable plastics for IV administration, and the energy requirements of the infusion pump. The high proportion of wasted propofol may have environmental impacts other than GHG emissions.

Some quantity of unprocessed propofol likely makes its way into the environment, where it has moderate persistence. It is unknown what course the metabolites take within ecosystems or whether these are harmful. There is significant uncertainty in this analysis, particularly regarding the synthesis of propofol and the volatile drugs. Our results, therefore, should be interpreted with caution. Future research would benefit from commercial-scale synthesis data from pharmaceutical companies. Nevertheless, from our results it appears likely that techniques other than inhalation anesthetics, such as IV anesthesia, neuraxial, or peripheral nerve blocks, would be least harmful to the climate.

Finally, there are also important human health considerations from reducing GHG emissions. The World Health Organization estimates climate-related mortality at 0.3 percent of all annual deaths (150,000/year) and expects this number to increase. For example, the incidence of cardiovascular disease and asthma may increase due to the emissions from coal-fired power plants and through temperature changes, and infectious diseases may spread more readily due to altered habitats resulting from climate change. Clinical decisions should consider the full environmental and human health impacts from anesthetic use.

Excerpt from Anesthesia & Analgesia, May 2012, Volume 114 Number 5