Environmental sustainability

Introduction

The climate crisis is quite possibly the largest and most protracted threat to human life yet described. Largely due to anthropogenic green house gas emissions the Earth's climate continues to warm, and modern medicine plays a nontrivial part in overall carbon emission. If global health care were a country, it would represent the fifth largest carbon emitter on the plant. Green house gas (GHG) emission represents a key contribution to global warming, and one important and relevant source of GHGs is anesthetic gases released into the environment.

Anesthetic Gases

Commonly used modern anesthetic gases include nitrous oxide and fluorinated gases such as sevoflurane, isoflurane, and desflurane, all of which have been recognized as greenhouse gases.

In clinical use, volatile anesthetics undergo minimal metabolism in the human body and are largely eliminated by exhalation unchanged (>95% unchanged). These gases are collected via a gas scavenging system, however this system then exhausts into the atmosphere with little to no further processing. There, these gases can absorb and reduce outbound infrared thermal energy and contribute to the increasing atmospheric temperatures. Halothane, and Isoflurane to a lesser extent, are halogenated chlorofluorocarbon that are known to both damage the ozone layer as well as function as a GHG. Nitrous oxide also depletes the ozone layer and is reported to be the single most important ozone depleting substance currently emitted. Atmospheric lifetime varies between the various volatiles, and desflurane is reported to be the longest lived at 9-21 years, followed by isoflurane at 3-6 years then sevoflurane with the shortest lifetime of 1-5 years. Even worse, nitrous oxide has an atmospheric lifetime of 114 years. The overall contribution to the GHG effect is quantified with the global warming potential which serves to compare the contribution of a GHG with the same mass of CO2 over a period of time. The 100 globing warming potential was 893 CO2 equivalents/kg for desflurane, 191 CO2 equivalents/kg for isoflurane, and 48 CO2 equivalents/kg for sevoflurane. For context, this means that 1 hour of desflurane anesthesia is equivalent to driving 235-470 miles while 1 hour of sevoflurane anesthesia represents approximately 18 miles of driving (flows of .5-2l/min).

Minimizing the Environmental Impact

• The American Society of Anesthesiologists recommends avoiding nitrous oxide as a carrier gas and minimizing fresh gas flow rates while using nitrous.
• The best approximations of ideal FGF rates would be achieved by reducing FGF to 2 L/min with sevoflurane and to 0.5−1 L/min with desflurane and isoflurane.
• Utilizing closed circle systems further increases the efficiency of utilized anesthetic gases.
• Minimizing nitrous and desflurane given their higher environmental impact is recommended, of course unless this will have negative outcomes on the patient.

Summary

Modern health care has made considerable progress in improving human life, however this industry is also responsible for significant pollution and waste. Anesthetic gases represent overall a small but significant contributor to the growing crisis of global warming. When possible, taking patient safety into account, decreased use of nitrous oxide and desflurane as well as lower fresh gas flows will help to reduce anesthesia's role in the growing climate crisis.