Global warming impact of fluorinated gases in ophthalmic surgeries at a tertiary eye center in India

Abstract

Purpose:

Global warming is one of the greatest health threats of the 21^st century. The ophthalmic sector contributes to the emission of greenhouse gases, thus altering the natural environment. There is currently no data on global emissions of fluorinated gases in ophthalmic surgery. This retrospective study from 2017 to 2021 aims to report the carbon dioxide (CO₂) equivalence of sulfur hexafluoride (SF₆), hexafluoroethane (C₂F₆), and octafluoropropane (C₃F₈) at a tertiary eye center.

Methods:

Data collected from 1842 surgical procedures that used injections of fluorinated gases were analyzed. Environmental impact (global warming potential over 100 years) was calculated by converting milliliters to grams by using modified ideal gas law at standard temperature and pressure for the canisters and then to their CO₂ equivalence.

Results:

Though 70% of surgeries used C₃F₈, the least greenhouse effect causing fluorinated gas, the total carbon emission was 1.4 metric tons. The most common indication was macular hole surgery (36.86%).

Conclusion:

This study paves a step toward analyzing the problem statement, thus awakening us to contemplate options to make ophthalmic surgeries greener.

Global warming is one of the greatest health threats of this century.[1,2] India is regarded as highly susceptible to global warming due to the sensitivity of its population and economy to the impacts of climate change.[3] To evade the consequences ensuing from it, all industries must devise strategies to reduce greenhouse gas emissions. The generation of enormous amounts of both biodegradable and non-biodegradable waste, which causes a catastrophic effect affecting environmental health, must be dealt with. The ophthalmology sector is increasingly having an adverse effect on the environment. Refinement of referral pathways, upskilling community optometrists, establishment of peripheral imaging and treatment “hubs,” utilization of home devices alongside artificial intelligence algorithms, and risk stratification of patients in ophthalmology outpatient settings can reduce unnecessary cost, waste production, and travel-associated carbon emissions.[4] If the healthcare sector does not introduce climate-friendly policies and practices, it paradoxically will continue to contribute directly and indirectly to negative health impacts through its emissions of CO₂ and other greenhouse gases.[5] Operating theaters are a resource-intensive area of healthcare, and because it is believed that they are necessary for high-quality care, their environmental effects are not given the attention they require.[6] Ophthalmic procedures such as phacoemulsification cataract surgery and vitreoretinal surgeries involving fluorinated gases were found to cause a greater environmental impact.[4] It is time to embrace climate change alleviation without compromising quality care by embarking on the path of greener healthcare practices.

Methods

This was a retrospective study spanning a duration of 5 years (January 2017–December 2021) at a tertiary eye care facility in South India. The aim of the study was to report the environmental impact of fluorinated gases used for intraocular tamponade procedures.

Ethical consideration

As this was a retrospective anonymous study, all procedures were completed prior to the inclusion. Patients were diagnosed and treated according to local guidelines. Agreements and written consent from patients were acquired prior to all procedures as clinically indicated. The study does not report on the use of any new or experimental protocols and hence was exempted from ethical approval.

Data acquisition was done with the help of electronic patient records, operation theater (OT) database, and store inventory. The study encompassed all ophthalmic procedures involving fluorinated gases, including vitreoretinal and anterior segment procedures. Air tamponade and silicone oil-based vitreoretinal procedures were excluded.

The study covered a wide range of surgical procedures within the study period, including 23-G, 25-G, and 27-G pars plana vitrectomy and corneal procedures (descemetopexy and anterior chamber reformation). The gas used for tamponade was as per the discretion of the surgeon, and the dilution was as per the case requirement (standard dilution being 12% for C₃F₈, 16% for C₂F₆, and 20% for SF₆).

The eye unit utilized the three fluorinated gases (SF₆, C₂F₆, and C₃F₈) during the study period:

• 30-mL canisters of SF₆

• 30-mL canisters of C₃F₈

• C₂F₆ was rarely used (procured only when required)

Environmental impact calculations

The calculator developed by Moussa et al.[7] was used to convert milliliters (mL) of gas to grams (g) of mass by using the modified ideal gas law formula at standard temperature and pressure for the canisters, and then to their equivalent amount of carbon dioxide (CO₂) in the atmosphere.

Due to the variations in canister pressure and atmospheric pressure, mass is the metric used to permit comparisons because it is constant regardless of gas pressure and temperature.

Intraocular gas masses were converted to their global warming potential (GWP) over 100 years (GWP100). GWP is a ratio of how much heat a gas can absorb relative to CO₂ over time; the GWP of CO₂ is always 1. As different gases have different atmospheric lifespans, GWP can increase or decrease with time, relative to CO₂. Fluorinated gases have atmospheric lifetimes of several thousand years, compared to CO₂, which persists for approximately 100–300 years (IPCC. Climate Change 1995: The IPCC Second Assessment Report. 1995); thus, their GWP increases significantly with time. Fluorinated gases will, therefore, have a lower GWP over 20 years (GWP20) compared with 100 (GWP100) or 500 (GWP500) years, as shown in Fig. 1.[8]

Figure 1.

Global warming potentials at different time periods

A staff survey revealed that the standard volume of gas loaded in the 50-mL syringe for procedures using diluted gases would be 6, 8, and 10 mL for C₃F₈ (12%), C₂F₆ (16%), and SF₆ (20%), respectively, and for 100% gas injection of SF₆, C₂F₆, and C3F₈, 1 mL of the gas was loaded in the syringe; thus, the same was taken into account while calculating the volume of gas consumption, that is, the amount of gas withdrawn per surgery based on standard protocols multiplied by the number of surgeries.

The volume was then entered into the calculator designed by Moussa G et al.,[7] which comprises a Microsoft Excel® (Microsoft Corporation, Redmond, WA) spreadsheet program that simplifies and enables surgeons to reliably convert the volume of gases to mass and then to their CO₂ equivalent from fluorinated gases. The results were then cross-tabulated for analysis.

Thus, the global warming potential and CO₂ equivalence were calculated from the hospital’s operating theaters, enabling assessment of the impact these gases have on the environment.

Results

There were 1842 patients in all who received fluorinated gas tamponade-required surgery. Table 1 lists the number of operations carried out during the research period as well as the type of intraocular gas used. It was discovered that C₃F₈ gas was utilized as a tamponading agent in 1287 (69.86%) procedures, followed by SF₆, which was used in 449 (24.37%) procedures. Only 106 (5.75%) operations used C₂F₆. Table 1 also displays the CO₂-equivalent mass (GWP100) measured using the Moussa et al.[7] calculator. It was estimated that the gases used during the research period produced a total mass of 1403.86 kg (1.4 metric tons) of CO₂ equivalent, of which SF₆ contributed 737.34 kg (52.52%), C₂F₆ contributed 64.75 kg (4.61%), and C₃F₈ contributed 601.77 kg (42.87%). The use of SF₆ as a tamponading agent was only in 24.37% of the operations, yet it was discovered that this had a maximum global warming potential of 737.34 kg.

Table 1.

Total number and their CO₂-equivalent mass in kilograms (GWP100) for the surgeries performed using fluorinated gases in the study period

GAS		SF6				C2F6				C3F8				Total
		Number		CO2 kg (GWP100)		Number		CO2 kg (GWP100)		Number		CO2 kg (GWP100)		Number		CO2 kg (GWP100)
2017		9		14.78		1		0.61		29		13.56		39		28.95
2018		52		85.40		23		14.05		118		55.17		193		154.62
2019		195		320.22		48		29.32		528		246.88		771		596.42
2020		64		105.10		23		14.05		256		119.70		343		238.85
2021		129		211.84		11		6.72		356		166.46		496		385.02
Total		449		737.34		106		64.75		1287		601.77		1842		1403.86

During the study period, the CO₂-equivalent mass computed per surgery was 1.64 kg for SF₆, 0.61 kg for C₂F₆, and 0.47 kg for C₃F₈.

As shown in Table 2, the fluorinated gas procedures were also divided into categories depending on the indications for each. Macular hole surgeries were the most prevalent indication (36.66%), and C₃F₈ was the most often employed gas in these operations (70.79%). The second most common indication was vitreous hemorrhage (12%) and diabetic tractional retinal detachments (11.5%). Indications requiring the use of 1 ml of 100% gas like anterior segment procedures, pneumoretinopexy and submacular hemorrhages produced 2.9%, 4.2% and 4.8% of the total SF6, C2F6 and C3F8 associated carbon emissions respectively in our study.

Table 2.

Number of surgeries using fluorinated gases and their CO₂-equivalent mass in kilograms (GWP100) based on indications over the study period

Indication		SF6				C2F6				C3F8
		Number		CO2 kg (GWP100)		Number		CO2 kg (GWP100)		Number		CO2 kg (GWP100)
A/S		92		15.10		0		0		11		8.02
Diabetic TRD		72		118.23		5		3.05		139		100.99
ERM Removal		27		44.33		0		0		51		36.47
Macular Hole		126		206.91		73		44.59		480		317.48
Pneumopexy		34		5.58		12		0.91		142		14.65
RRD		17		27.92		2		1.22		155		81.36
Sub mac Hg		6		0.98		3		1.83		74		6.47
Trauma		4		6.56		1		0.61		8		6.07
Vit Hg		63		103.45		7		4.27		155		105.20
Vit Lavage		8		13.13		3		1.83		72		38.81

A/S=Anterior Segment procedures, TRD=Tractional Retinal Detachment, ERM=Epi-retinal Membrane, RRD=Rhegmatogenous Retinal Detachment, Pneumopexy=Pneumoretinopexy for retinal detachment, Sub mac=Submacular , Vit=Vitreous , Hg=Hemorrhage

Fig. 2 shows a comparison of CO₂ emissions in kilograms (GWP100) if a single fluorinated gas was used for all procedures in the study period, thus illustrating SF₆ (3024.84 kg) to be the most potent greenhouse gas among the fluorinated gases in question and the need for strict regulation on its usage as cited in the Kyoto Protocol (UNFCCC. What is the Kyoto Protocol? United Nations Climate Change. 2021).

Figure 2.

Scenarios comparing the CO₂ emissions in kilograms (GWP 100) if a single fluorinated gas is used for all procedures in the study period

Discussion

This retrospective study assessed the CO₂-equivalent mass for various fluorinated gases used in ophthalmic surgeries at a tertiary eye care facility in South India, which would then suggest the possibility of global warming over the next 100 years. Although similar studies have been conducted in the UK,[9] this is the first study of its kind to be conducted in India, allowing for easier investigation of the issue statement—the harmful effects of surgical gases on the environment. In a study by Javid and Khan,[10] the estimated carbon emission trends were found to be upward-sloping for China and India. In addition, on quantifying the impact of energy efficiency on environmental quality in the top five greenhouse gas-emitting countries, India ranks third, next after China and the USA. This correlates with Thaker, J et al.,[3] who also ranked India as the third largest contributor of annual emissions in the world.

The ophthalmic community contributes to drastic climate change due to energy consumption and the use of medical waste and other disposables. Due to the limited intraocular volume employed, the environmental impact of fluorinated gases in ophthalmic surgery has received little attention. However, it is clear that carbon emissions from these can be substantially more than that anticipated given the extremely high GWP100 of fluorinated gases and the gas waste associated with delivery systems.

Based on the study by Moussa et al.,[9] it was shown that 30-mL canisters were the most efficient way for delivery systems for fluorinated gases. Our study, which used 30-mL canisters for gas delivery, found that using fluorinated gas in a tertiary care eye setup alone resulted in 1.4 metric tons of carbon emissions over the course of 5 years. This occurred despite the maximum use of C₃F₈ (69.86%), which is the least greenhouse effect-causing gas. The most common indication for the use of gases in ophthalmic surgery was identified as macular hole (36.86%).

Although SF₆ was used in only 24.37% of surgeries in our study, it contributed to 737.34 kgs (52.52%) of carbon emissions. This is consistent with Moussa et al.,[11] who demonstrated that SF₆, despite being used in 38.6% of procedures, contributed to 68.8% of CO₂ emissions. As SF₆ is the shortest-acting fluorinated gas tamponade and yet the most potent greenhouse gas, surgeons can consider using air tamponade more frequently as an alternative when clinically safe to do so. To repair some rhegmatogenous retinal detachments, increasingly, surgeons are turning to air tamponade, which has been shown to produce comparable surgical results to gas tamponade.[12] The carbon impact due to this tamponade method would be significantly reduced; however, more research is necessary. Additional research on employing C₂F₆ at lower concentrations instead of SF₆ may also be conducted.

Perspective

We compared the carbon emissions to daily activities to better comprehend the issue. It is said that driving a diesel car for 6000 miles produces emissions equal to 1.4 metric tons of CO₂. In addition, the use of an electric heater for 6 hours a day for a year can generate approximately 1400 kg of CO₂ emissions. (https://www.carbonfootprint.com/calculator.aspx) (https://ecotree.green/en/how-much-co2-does-a-tree-absorb) [Fig. 3].

Figure 3.

Perspective to show the CO₂ emission from a tertiary care eye facility due to injection of fluorinated gases over 5 years and the means to offset the same

Producing emissions equal to 1.4 metric tons of CO₂ by driving a diesel car for 6000 miles is a rough estimate. The actual emissions from a diesel car can vary significantly based on factors such as the car’s fuel efficiency, type of driving (city vs. highway), and emissions standards of the vehicle.

Generating approximately 1400 kg (1.4 metric tons) of CO₂ emissions from using an electric heater for 6 hours a day for a year is an estimate based on the electricity consumption of the heater and the carbon emissions associated with the electricity source.

We used different inputs, various car models, in the mentioned referenced calculators (https://www.carbonfootprint.com/calculator.aspx) and averaged the same to give a perspective. The readers are encouraged to use the calculator for their vehicle model to estimate the same.

Thus, having understood the problem statement, it is important to devise strategies to tackle the same.

Starting programs such as the Institutional Afforestation Drive is one of the most straightforward and efficient ways to address the issue without sacrificing health care or altering protocol. Once the carbon emissions are known, any healthcare facility can efficiently offset them by planning an annual afforestation drive to reduce the emissions.

A tree typically absorbs between 10 and 40 kg of CO₂ per year, depending on a wide range of variables. Institutes can estimate the species and quantity of trees needed to offset their carbon footprint and plant the same, depending on the local climate and the availability of saplings. Utilizing the online calculators that are readily available makes this task convenient. (https://bcrp.baltimorecity.gov/forestry/treebaltimore/calculator) (https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle).

For example, to estimate the number of trees we would need to plant each year over 100 years to offset 1400 kg of CO₂ emissions, we would need to make some assumptions about the carbon sequestration potential of the trees we plant. For simplicity, we assume that we plant trees that can sequester 5 kg of CO₂ per year for their entire lifespan. In this case, we would need to plant around 14 trees per year for 100 years to offset 1400 kg of CO₂ emissions. However, the number of trees needed to offset carbon emissions can decrease over time as the trees mature and reach their full carbon sequestration potential.

Creating an eco-friendly environment in the healthcare system leads to both energy savings and monetary savings. Various concepts are being implemented such as waste reduction and energy conservation by promoting the use of compact fluorescent lamp lights and light-emitting diodes in both surgical and outpatient department setups.

Thus, we intend to raise awareness of the environmental implications of ophthalmic procedures and highlight the need for innovative solutions to tackle the challenging issue of global warming.

Limitations of the study

The carbon footprint associated with the production, delivery, storage, removal, and disposal of single-use canisters and other aspects of the procedure, such as anesthesia technique, OT utilization time, and equipment used, were not measured; further research is necessary to address these aspects.

Conclusion

This study acts as a pioneer study in identifying the problem statement and paves the way for multicentric comparisons of the carbon footprint data in ophthalmic surgical care. It also directs toward designing protocols on the usage of air as a preferred agent for short-term tamponade in appropriate cases to mitigate carbon emissions. In addition, it motivates medical facilities such as operating rooms and hospitals to assess their carbon footprints and devise strategies to overcome the same, thus making healthcare practice greener.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.