Can you imagine a tooth being extracted without an anesthetic? Or, worse, a limb being amputated? A horrific thought! Yet that was what patients had to contend with until the mid 19th century when nitrous oxide and ether appeared on the scene and ushered in the era of painless surgery. Without a doubt, the advent of anesthesia is one of the great moments in the history of science. But as with just about any discovery, be it that of radioactivity, electricity, antibiotics or vaccines, issues arise as time passes and new information comes to light. That’s when the need for a risk-benefit analysis emerges.
Since inhaled gases are metabolized only minimally, with about 95% being exhaled, the question of their eventual fate arises. Do they have an effect on the environment and do they present an occupational hazard? The anesthesia machine captures the exhaled gases so they don’t build up in the operating room, but the problem is that they end up being vented outside. The issue here is that some of the anesthetic gases can damage the ozone layer that protects us from excessive exposure to ultraviolet light. And all are “greenhouse gases” implicated in climate change.
The mechanism of ozone depletion has been worked out. As far as nitrous oxide goes, it reacts with oxygen atoms in the atmosphere to form nitric oxide that in turn reacts with ozone to yield nitrogen dioxide and oxygen. Obviously, this leads to loss of ozone. Isoflurane, a common anesthetic, destroys ozone by a different route. Under the influence of ultraviolet light, it releases chlorine atoms to start a chain reaction in which ozone is consumed.
While not all the anesthetic gases have ozone depleting effects, with sevoflurane and desflurane being absolved of this crime, they all play a role in global warming since they all reflect rising heat back towards the ground. Relative to carbon dioxide, methane, and nitrous oxide from decomposing fertilizer, the contribution is very small, but still worthy of attention. Annual greenhouse gas emissions from waste anesthetic gases for a midsize hospital can contribute as much to global warming as driving one thousand passenger cars for a year. And there are many hospitals in the world. Furthermore, the anesthetic gases stay around in the atmosphere for years, nitrous oxide being the most notorious with a lifetime of over a hundred years. Since sevoflurane has the shortest lifetime and has no effect on the ozone layer, it is now the preferred anesthetic.
Besides environmental concerns, there is also the question of occupational exposure. Any gas that leaks into the air in an operating room can be inhaled by all present. Even brief exposure can cause headaches, irritability, fatigue, nausea, difficulty in judgement, impaired dexterity and drowsiness. In the long term, the kidneys, liver, nervous and reproductory systems may be affected. Levels below which effects do not occur have been established, for example 25 parts per billion of nitrous oxide and 2 parts per billion for halothane, desflurane, isoflurane and sevoflurane. Studies have shown that these levels are very rarely exceeded since anesthesia machines are equipped with scavengers to catch exhaled gases, and operating rooms are generally well ventilated.
Not all anesthetics are inhaled, some like propofol, etomidate, ketamine and midazolam are administered intravenously. These do not have any ozone-destroying or global warming effects, but they can still contaminate the environment. If after use, their bottles or vials, which are never completely empty, are improperly discarded, their chemical remnants can end up in landfills and leach out into groundwater. This, of course, doesn’t only apply to anesthetics, but to all medications. Studies have found trace amounts of numerous drugs in drinking water, although that does not necessarily mean that they present a risk. After all, only the dose makes the poison.
That brings us back to our risk-benefit analysis. In this case, it makes for a really easy evaluation. Would you opt for surgery without anesthesia in favour of reducing the minimal contribution that anesthetic gases make towards ozone depletion and global warming? I think not.