Background

The use of inhaled organic (carbon-containing) compounds for general anesthesia is over a century old. Early experiments used diethyl ether (quite flammable!!) or chloroform. Although chloroform had other disadvantages, it was much less flammable than ether. Eventually, after decades of experimentation, pharmaceutical companies settled on a family of compounds called halogenated ethers; they were potent, nonflammable and relatively nontoxic. These properties were the result of the substitution of halogen atoms (chlorine, bromine and/or fluorine) for most of the hydrogen atoms on the ether molecule. The resulting compounds were similar to the refrigerant “Freon” or the “halon” used in firefighting. The structures of the most common of these are shown below:

Isoflurane Desflurane Sevoflurane

These compounds are taken up through the lungs of the patient after vaporization into mixtures of air, oxygen and (sometimes) nitrous oxide. The drug travels from the lungs into the bloodstream and is distributed throughout the body: most importantly to the brain. In inhaled concentrations from 0.5 to over 5%, these halogenated ethers produce reliable general anesthesia free from severe side effects. Currently these drugs are used worldwide millions of times per year.

The problem occurs when these drugs are no longer needed. After surgery is completed, the patient is given pure oxygen; and, since the body does not significantly metabolize these drugs, they are exhaled and discarded. The disposal of these agents is interesting…

The operating room environment is closely monitored and regulated, since some evidence of adverse effects from chronic low-level exposure in surgical personnel appeared about 30 years ago (ref). Anesthetic gases are “scavenged” using a suction system and exhausted to the environment outside the hospital. Like other chlorofluorocarbons (CFCs), they are mixed into the atmosphere, where they undergo a complex set of reactions, eventually leading to their decomposition (ref).

But, unlike the more hazardous CFC emissions, the atmospheric effects of halogenated anesthetics don’t include ozone depletion (so much), but acid rain and greenhouse effects (potentially leading to global warming). The EPA and other international environmental agencies have systematically removed or replaced many CFCs and CFC-like compounds, but their attention has not focused on halogenated anesthetics…yet.

In the U.S. alone, the total production (and therefore use and release) amounts to 2000 tons/yr – the equivalent of almost 4,000,000 tons of excess CO2 release.