Environmental sustainability
Introduction
The climate crisis is quite possibly the largest and most protracted threat to human life yet described. Largely due to anthropogenic greenhouse 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.[1] Greenhouse gas emission represents a key contribution to global warming, and one important and relevant source of GHGs is anesthetic gases released into the environment.[2]
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 greenhouse gas. Nitrous oxide also depletes the ozone layer and is reported to be the single most important ozone depleting substance currently emitted.[3]
| Anesthetic gas | Atmospheric lifetime | 100-year global warming potential[4] |
|---|---|---|
| Desflurane | 9-21 years | 893 CO2 equivalents/kg |
| Isoflurane | 3-6 years | 191 CO2 equivalents/kg |
| Sevoflurane | 1-5 years | 48 CO2 equivalents/kg |
| Nitrous oxide | 114 years | 298 CO2 equivalents/kg |
The overall contribution to the greenhouse gas effect is quantified with the global warming potential which serves to compare the contribution of a greenhouse gas with the same mass of CO2 over a period of time. 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).[5]
Footprint of General, Spinal, and Combined Anesthesia
Despite their significant impact, factors other than anesthetic gas can also significantly contribute to the overall environmental impact of anesthesia. A recent study[6] compared general, regional, or a combination and found no significant difference in environmental impact.
Total knee replacement patients were split into general anesthesia with sevoflurane, spinal anesthesia (with Propofol sedation), or a combination of both. Average CO2 emissions (measured in kg CO2) were 14.9kg (95%CI 9.7-22.5) for general, 16.9kg (95%CI 13.2-20.5) for regional, and 18.5kg (95%CI 12.5-27.3) for the combined group.
It follows that sources other than volatiles must be a large contributor. In the spinal and combined groups, the largest additional factor was the electricity required in the "reusables" group (described as washing/sterilization of reusable gowns, plastic spinal trays, etc.) Across all three groups electricity used in the generation of single used items represents 20-25%.
| GA | Spinal | GA + Spinal | |
|---|---|---|---|
| Sevoflurane | 35% | 0% | 19% |
| Single-use
Items |
26% | 22% | 25% |
| Warmer | 20% | 21% | 19% |
| Drugs | 9% | 8% | 8% |
| Reusables | 5% | 25% | 25% |
| Others | 5% | 6% | 4% |
| Total (in Kg) | 14.9kg
(95%CI 9.7-22.5) |
16.9kg
(95%CI 13.2-20.5) |
18.5kg
(95%CI 12.5-27.3) |
Several modifications can help reduce this output. Reducing O2 flows during spinal anesthesia from 10L to 6L can save approximately 1 "mile"/hr.
Overall they found the average anesthetic represented 17kg CO2 which represents driving 42 miles (importantly this study was done without N2O or Desflurane). Several modifications can help reduce this output. Reducing O2 flows during spinal anesthesia from 10L to 6L can save approximately 1 "mile"/hr. Reducing FGF 1L/min during GA can save 3 "miles"/hr.
Significant limitations to this study include: no N20 or desflurane use, small sample size of 30, and conducted in Austria which can limit external validity.
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.[5]
- 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.
- General VS spinal VS GA+Spinal did not seem to make a significant difference.
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, single use items, and reusable items represent an overall 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.
- ↑ Pichler P-P, Jaccard IS, Weisz U, Weisz H. International comparison of health care carbon footprints. Environ Res Lett 2019; 14, 064004
- ↑ Sherman, Jodi D.; Sulbaek Andersen, Mads P.; Renwick, James; McGain, Forbes (2021). "Environmental sustainability in anaesthesia and critical care. Response to Br J Anaesth 2021; 126: e195–e197". British Journal of Anaesthesia. 126 (6): e193–e195. doi:10.1016/j.bja.2020.12.025. ISSN 0007-0912.
- ↑ Chipperfield M. Atmospheric science: nitrous oxide delays ozone recovery. Nat Geosci. 2009;2:742–743
- ↑ Weinberg L, Tay S, Aykanat V, et al. Changing patterns in volatile anaesthetic agent consumption over seven years in Victorian public hospitals. Anaesth Intensive Care. 2014;42:579–583.
- ↑ 5.0 5.1 Ryan SM, Nielsen CJ. Global warming potential of inhaled anesthetics: application to clinical use. Anesth Analg. 2010;111:92–98.
- ↑ McGain F, Sheridan N, Wickramarachchi K, Yates S, Chan B, McAlister S. Carbon Footprint of General, Regional, and Combined Anesthesia for Total Knee Replacements. Anesthesiology. 2021 Dec 1;135(6):976-991. doi: 10.1097/ALN.0000000000003967. PMID: 34529033.
Top contributors: Mitchel DeVita and Chris Rishel