Inhaled anesthetics widely used for surgery—particularly the anesthetic desflurane—make a measurable contribution to global warming, according to a study in the July 2010 issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

The anesthetics used by a busy hospital contribute as much to global warming as the emissions from hundreds of cars per year, according to the new study by anesthesiologist Susan M. Ryan, MD, of University of California and computer scientist Claus J. Nielsen of University of Oslo. While no one’s suggesting that patients shouldn’t receive needed anesthetics because of the risk of climate change, some simple steps could help to limit their environmental impact.

The researchers determined "infrared absorption cross-sections" to calculate the global warming potential (GWP) of three major inhaled anesthetics: sevoflurane, isoflurane, and desflurane. As a group, these anesthetics are recognized greenhouse gases. However, because anesthetics are considered medically essential and used in relatively small amounts, few previous studies have evaluated their contributions to global warming.

However, Ryan and Nielsen point out that these inhalant anesthetics undergo very little metabolic change in the body—the gases exhaled by the patient are almost identical to those administered by the anesthetist. The anesthetics "usually are vented out of the building as medical waste gases," the researchers write. "Most of the organic anesthetic gases remain for a long time in the atmosphere where they have the potential to act as greenhouse gases."

The results showed that desflurane had a much longer "lifetime" in the atmosphere than the other anesthetics studied: 10 years, compared to 1.2 years for sevoflurane and 3.6 years for isoflurane. Considering the flow rates at which the different anesthetics were given, desflurane had about 26 times the GWP of sevoflurane and 13 times the impact of isoflurane.

The "carrier gases" with which anesthetics are given also affected their global warming impact. In particular, giving nitrous oxide as a carrier gas increased the GWP of isoflurane or sevoflurane, but decreased the GWP of desflurane. However, since nitrous oxide continues to have an impact over a longer timeframe, it "may not be an environmentally sound tradeoff for desflurane," Ryan and Nielsen write.

Simple Steps Can Help to Limit Carbon Footprint

It may seem strange to be concerned about the global warming potential of medically necessary anesthetics, but anesthesia departments have a substantial overall carbon footprint, according to the study. Depending on the types of anesthetic used, an average midsize hospital has an environmental impact comparable to that of 100 to 1,200 cars per year. Using desflurane for one hour is equivalent to 235 to 470 miles of driving.

Ryan and Nielsen suggest some "simple, knowledge-based decisions" that anesthesiologists can follow to minimize their environmental impact—particularly avoiding nitrous oxide unless there are medical reasons to use it and avoiding unnecessarily high anesthetic flow rates, especially with desflurane. Ultimately, the innovation with the greatest potential to lower the environmental impact of anesthetics is the development of new technologies that capture anesthetic gases for reuse, rather than releasing them into the atmosphere.

"Inhaled anesthetics are ‘greenhouse gases’ that facilitate the trapping of solar energy and contribute to global warming," comments Steven L. Shafer, MD, of Columbia University, Editor-in-Chief of Anesthesia & Analgesia. "This study calculates how much inhaled anesthetics contribute to greenhouse gas emissions, and offers specific suggestions about how anesthesiologists can reduce the impact of anesthesia care on global warming."

[Source: Anesthesia & Analgesia]