News

The environmental impact of anesthetic gases

5/22/12

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 8 per­cent of the nation’s green­house gas emis­sions. According to 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.

Eck­elman looks 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 recent paper in a spe­cial issue of the journal Anes­thesia & Anal­gesia, Eck­elman and col­leagues at Yale Uni­ver­sity per­formed life-​​cycle assessments of the major anes­thetic gases used in the health-​​care industry: nitrous oxide (laughing gas), des­flu­rane, isoflu­rane and sevoflu­rane, as well as a liquid anes­thetic alter­na­tive, propofol.

“Any life-​​cycle assess­ment, Eck­elman said, is a series of trade­offs. 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 said.

Life cycle green­house gas (GHG) emis­sions of anes­thetics, including waste anes­thetic gas emis­sions of halo­genated drugs and nitrous oxide (N2O).

During a talk at the Inter­na­tional Sym­po­sium on Sus­tain­able Sys­tems and Tech­nology in Boston last week, Eck­elman deliv­ered the paper’s results, showing 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,” said Eck­elman, who chaired a por­tion of the sym­po­sium, “and they’re quite potent.” Des­flu­rane, for example, has a global warming poten­tial more than 2,500 times that of carbon dioxide, he said.

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, said 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, Eck­elman and his 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, two of the university’s cen­tral research themes, is part of a gen­eral inter­na­tional effort to bring life-​​cycle assess­ment to bear on var­ious aspects of health-​​care prac­tice. Civil and envi­ron­mental engi­neering pro­fessor Matthew Eck­elman deliv­ered the results of an anesthetic-​​drug life-​​cycle assess­ment to the Inter­na­tional Sym­po­sium on Sus­tain­able Sys­tems and Tech­nology last week.