The carbon footprint of cataract surgery in Wellington
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article
The carbon footprint
of cataract surgery
in Wellington
Matthew Latta, Caroline Shaw, Jesse Gale
ABSTRACT
INTRODUCTION: Efforts to improve the sustainability of ophthalmic care require methods to measure its
environmental impact and a baseline measurement to compare against in the future. We aimed to measure
the carbon footprint of cataract surgery in Wellington.
METHODS: We used Eyefficiency, an application using established footprinting methods, to estimate the
emissions produced by phacoemulsification surgery in two public and two private hospitals. We measured
(1) power consumption, (2) procurement of disposable items and pharmaceuticals, (3) waste disposal
emissions and (4) travel (other potential sources were excluded). Where possible we used New Zealand
emissions coefficients.
RESULTS: We recorded data from 142 cataract surgeries. The average emissions produced by cataract
surgery in the region was estimated to be 152kg of carbon dioxide equivalent. This is equivalent to 62L
of petrol and would take 45m2 of forest one year to absorb. The great majority of emissions were from
procurement, mostly disposable materials, and the second greatest contribution was from travel (driving).
CONCLUSION: Estimating the carbon footprint of cataract surgery is becoming easier, but improved
methods for measuring the footprint of procured supplies are needed. There are significant opportunities
for emissions reduction in the most common surgical procedure in New Zealand.
C
limate change is the largest global Attempts to derive a carbon footprint
health threat in the 21st century,1,2 of cataract surgery have shown widely
and there is broad support for urgent divergent results in different countries: in
action to mitigate climate change though Cardiff, United Kingdom (UK), the esti-
emissions reduction, even among oph- mated footprint was 182kgCO2e,11 whereas
thalmologists.3–5 The healthcare sector is a the footprint of the Aravind Eye Care
major source of physical waste and green- System (AECS) of Southern India was only
house gas emissions.6 In New Zealand and 6kgCO2e.12 This vast difference between
Australia, healthcare accounts for around the UK’s and India’s surgery footprints
10% of national economic activity and has been attributed to AECS reusing most
contributes around 5% of total greenhouse items (including blades and tips), recycling
emissions, which is more than aviation.7,8 much of their waste and having high time
The National Health Service of England’s efficiency and throughput, reduced power
target is for their healthcare sector to be consumption and cheaper locally-sourced
carbon neutral by 2040,9 and recently the surgical materials. There are also some
New Zealand Government announced its differences in how the AECS and UK foot-
entire public sector will move to achieve prints were calculated.13
carbon neutrality by 2025 (the details for In this cross-sectional study, we aimed to
district health boards have not yet been estimate the carbon footprint of cataract
announced).10 surgery in all hospitals in the Wellington
Due to both high surgical volumes and region, New Zealand (two public and two
considerable disposable consumption, private participated). This was to establish
cataract surgery is the greatest source a baseline measure or benchmark for
of emissions within ophthalmology. future sustainability auditing, to engage
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local stakeholders and to consider avenues
for improvement. A secondary aim was to
Carbon footprinting: inclusions and
compare public and private hospitals and exclusions
areas of relative strength and weakness. We included all elective phacoemul-
sification with lens implant operations,
Methods including complicated cases, as well as
the possible additions of suture removal,
Approvals bleb needling and intravitreal or subtenon
The study protocol was ethically approved injection. We excluded all larger combined
as a Minimal Risk Health Application by surgeries, such as cataract surgery with
the University of Otago Human Ethics planned vitrectomy or trabeculectomy or
Committee (Health): reference HD20/092. iris suturing. Bilateral cases were performed
Management of all three public hospitals and measured as two separate cases. The
and all three private hospitals in the main opportunity for reduced emissions
Wellington region agreed to participate. with bilateral surgery was reduced patient
Wellington Regional Hospital and Kenepuru travel. There were no manual cataract
Community Hospital, both of Capital & Coast extractions (without phacoemulsification)
District Health Board, and Bowen Hospital during the study. Operations under local or
and Southern Cross Hospital Wellington all general anaesthetic (article
We measured the emissions from the footprint of each consumable item was not
sterilisation of instruments in one hospital possible.
(using British emissions coefficients) and
found they were less than 0.25% of total
Waste data
Some hospitals recycled, and any emis-
emissions. As the amount was very small
sions from recycled waste were not
and we were uncertain about the accuracy
recorded. All other waste went to landfill,
of British coefficients in New Zealand, we
and we used New Zealand emissions coef-
decided to exclude this source of emissions.
ficients to calculate the emissions from
Carbon footprinting: emission transport and degradation of this waste. The
measurement weight of waste going to landfill after each
Electricity consumption case was measured with an electronic spring
Energy use was calculated by taking the scale. In hospitals with recycling, landfill
average monthly power consumption of waste was predominantly non-recyclable
each hospital or surgical unit; and taking a plastics, so we used an emission coefficient
proportion of the power consumption based for plastic in landfills. For hospitals that did
on the floor space allocated to ophthalmic not recycle, where landfill waste was mixed
surgeries; and the proportion of the week with more paper, we used an emission
scheduled for cataract surgery. In keeping coefficient for general waste. Wellington
with previous methods, we assumed that landfills perform gas recovery, which miti-
1m2 of operating theatre used twice the gates emissions from anaerobic degradation
energy as the average floor space of the of organic waste (not present in theatre
hospital, and that all hospitals had equiv- waste), and this reduced the emission coeffi-
alent electricity sources from the national cient we used for general waste.
grid.11 Carbon footprinting: emissions
Travel data coefficients
Travel methods were collected from Each source of emissions was measured
all operating theatre staff and the first 10 in the relevant units: kilowatt hours
patients at each hospital: all drove. Private (kWh) of electricity, kilometres (km) of
vehicle was then assumed to be the mode driving, dollars of procured supplies ($NZD
of travel for all other participants. Driving converted to £GBP of 2011), kilograms (kg)
distances were calculated to the suburb of landfill waste and tonne kilometres (tkm)
level to maintain privacy. Emissions from for freight. These measures were converted
staff travel were divided across the whole to greenhouse gas emissions (kgCO2e) using
operating list. Calculations used the fuel emissions coefficients (Table 1). Where
performance of an average New Zealand car possible, we used New Zealand emissions
(2010 Toyota Corolla 1.6L engine).14 coefficients sourced from the Ministry for
the Environment.14 Where local information
Procurement data was unavailable, we used the same interna-
The cost of pharmaceuticals and medical tional and UK coefficients that were used in
equipment per cataract operation were similar studies.15
calculated with data collected from theatre
managers. As described above, we excluded
procurement of other items such as infor-
Results
We collected data on 142 cataract opera-
mation technology, food and drink, linen
tions from the three months of November
and stationery, as they werearticle
cataract operations per session at the two with the lowest average waste (1.14kg) was a
public hospitals was 3.4. Simple cataract public hospital that did not recycle, and the
surgery was less common at the public hospital with the highest average (1.51kg)
hospitals, particularly Wellington Regional was the other public hospital, which did
Hospital, as there were many other types of recycle. Paradoxically, the public and private
surgery and combined surgery. hospitals that recycled both had heavier
Table 2 summarises the emissions results. waste bags than their counterparts, despite
The average footprint of cataract surgery some waste being diverted to recycling.
was 151.9kgCO2e. The proportions attributed The majority of the mass was from residual
to electricity use, travel, procurement of or collected irrigation fluid (balanced salt
supplies and pharmaceuticals and waste solution), gloves and gowns and soft plastic
disposal are also shown in Figure 1. packaging for sterile single use items. The
cassette and tubing for the phacoemulsifi-
As shown in Table 2, cataract surgery at
cation device were not recyclable, partly due
public hospitals had a slightly smaller carbon
to the fluid with biological material within
footprint than at private hospitals (145.2
them. At hospitals that recycled, the contents
kgCO2e compared to 158.6 kgCO2e). Travel
of the waste bags were mostly non-recy-
emissions per case were lower in private
clable soft plastics, and in hospitals that
hospitals, primarily due to longer lists of
didn’t recycle, the waste was a more hetero-
cataract operations (less staff travel per
geneous mixture of paper and different
case). Procurement emissions were lower in
plastics
public hospitals as perhaps they had greater
bargaining power or economies of scale for
negotiating lower costs per case. Pharmaceu- Discussion
tical costs were higher in private hospitals We found an average of 151.9kgCO2e
because more surgeons used medication of emissions from cataract surgery in
not funded by the national medicines and Wellington, not including perioperative
devices funding agency (PHARMAC), such as clinic visits. This footprint is similar to that
ketorolac, and because more surgeons used of an economy ticket on a one-hour flight, or
postoperative antibiotic drops. combustion of 62L of petrol, and would take
The waste produced by each operation 45m2 of forest one year to absorb. By extrap-
had an average mass of 1.32kg. The hospital olating this across the approximately 30,000
Table 1: Carbon emissions coefficients.
Power EC to convert kWh to kgCO2e EC reference
Electricity 0.101 NZ
Transport EC to convert km to kgCO2e EC reference
Car 0.238 NZ
Procurement EC to convert 2011 £GBP to kgCO2e EC reference
Pharmaceuticals 0.59 UK11
Medical equipment 0.54 UK11
Landfill EC to convert kg waste to kgCO2e EC reference
Plastic 0.008934 UK15
General waste 0.311 NZ
Waste freight 0.135 kgCO2e per tkm NZ
EC: emission coefficient. NZ: New Zealand. UK: United Kingdom. The ECs for plastic in landfill and procurement of
medical supplies were sourced from the UK11,15. All other ECs are from New Zealand.14
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Table 2: Carbon emissions (footprint) attributed to one phacoemulsification and lens implantation
surgery in Wellington (kgCO2e).
Overall Public Private
(all 4 hospitals) (2 hospitals) (2 hospitals)
Electricity consumption kWh kgCO2e kWh kgCO2e kWh kgCO2e
17.8 1.8 17.1 1.7 18.5 1.9
Travel (per case) km kgCO2e km kgCO2e km kgCO2e
Patient 48 11.4 51 12.2 45 10.7
Staff 48 11.4 72 17.2 23 5.5
Total 96 22.8 123 29.4 68 16.2
Procurement $NZD kgCO2e $NZD kgCO2e $NZD kgCO2e
Medical equipment 486 116.5 412 98.8 560 134.2
Pharmaceuticals 40 10.5 57 15.0 23 6.0
Total 526 127.0 470 113.8 583 140.2
Waste disposal kgCO2e kgCO2e kgCO2e
Waste emissions 0.191 0.184 0.198
Waste freight 0.013 0.022 0.004
Total 1.32 kg 0.204 1.33 kg 0.206 1.32 kg 0.203
Total 151.9 kgCO2e 145.2 kgCO2e 158.6 kgCO2e
Figure 1: The proportion of the average carbon footprint attributed to each source of emissions.
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cataract operations performed in New deals and negotiations with suppliers, and
Zealand each year, we estimate this surgery differences in price in different markets
creates 4,500 tonnes of CO2e a year, which probably account for greater emissions from
would take 134ha of forest growing for the procurement in New Zealand than UK.11
year to absorb. This is a major source of error in our study:
This footprint for cataract surgery in one hospital could demand sustainable
Wellington compares well to that found for supply chains for disposable items, and
Cardiff, UK, in 2012, which was 20% greater may pay a greater price for those supplies,
(182kgCO2e) when calculated using the same and the emission coefficient would incor-
method.11 However, much of this difference rectly estimate that the emissions were
could relate to the UK study including of greater. This decoupling of emissions and
both preoperative and postoperative clinic price will be a challenge for sustainability
visits (ie, increased travel and increased auditing in the future. Likewise, when all
electricity use in clinics). The very low foot- medical devices, including surgical supplies,
print of 6kgCO2e for phacoemulsification become bulk-purchased by PHARMAC, New
surgery at AECS highlights just how widely Zealand’s medicines and devices funding
the relevant factors can vary.12 Several agency, their cost will reduce but the level
reasons contribute to this huge difference: of emissions per se that they generate will
at AECS there is local production of many not change. A more complete method for
instruments and intraocular lenses; nearly assessing the footprint of procured supplies
every item is re-used to some extent; and is needed.
much of the waste is locally recycled. There Emissions from power consumption
are also efficiencies of throughput that (1.8kgCO2e) were very low compared to the
contribute to lower transport costs for staff. UK (66kgCO2e), due to a few reasons: (1) the
Emissions from travel were similar UK study included perioperative visits and
in Wellington (18kgCO2e) and Cardiff potentially included power use in the clinics
(23kgCO2e). In our study there were fewer and larger areas of the hospital; (2) British
emissions from travel in the private sector hospitals often use coal boilers for central
(Table 2), due to longer operating lists (ie, heating; (3) renewable energy (predom-
staff travel was distributed over more cases). inantly hydro) accounts for 82% of New
Travel distances for both staff and patients Zealand’s electricity supply, compared to just
at public and private hospitals were similar. 47% of the UK’s.16 The UK emission coef-
The main reasons for longer operating lists ficient indicates that electricity use in the
in the private sector were less-complex UK generates nearly six times more carbon
cases, fewer combined surgeries or non-cat- dioxide emissions than in New Zealand. New
aract surgeries, fewer general anaesthetics, Zealand government policy aims to increase
the absence of trainee surgeons who take the renewable energy sector to the theo-
longer to operate and lower turnaround retical maximum by 2030.
time with less administration required by Although waste disposal was a minor
the operating surgeon. Notably, we did not source of emissions, it was a significant mass
find any staff or patients using public or and large volume per case (one full rubbish
active transport across 61 individuals asked. bag that weighed 1.32kg on average). Two
The majority of emissions were from hospitals recycled but also had a somewhat
procurement (83.8%), mostly surgical greater mass of non-recyclable waste,
supplies such as gauze, dressings, gowns which could be related to other factors such
and gloves, blades, lens implants, tubing as larger bottles of irrigation fluid, more
and tips. The emission coefficient converted assisting surgeons with extra gloves and
the costs of procured supplies into emis- gowns, or differences in the packaging of
sions, based on international data for supplies. Recycling resulted in a different
the production and supply of medical type of waste going to landfill: more non-re-
equipment in general from 2011.15 cyclable plastic and less paper. And the
Therefore, in our study the emissions from different emission coefficient for this plastic
procurement mostly reflect the costs, rather waste in landfills reduced estimated emis-
than a careful analysis of product life- sions by 96% in hospitals that recycle.
cycles. These costs relate to bulk purchasing Despite recycling, we estimate the total
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amount of landfill waste created in New come. Initially, this will mean a commitment
Zealand from cataract surgery to be around to offsetting carbon emissions, but the
40 tonnes per year. Incineration without longer-term implications will include the
energy recovery would produce a great deal budgeting of emissions and procurement of
more emissions per kilogram of waste. low-emissions services and supplies.
A major implication of this study is that This study had limitations. The most
procurement is the best target for reducing obvious is the calculation of emissions from
emissions. Reducing procurement emis- procured products, which was based on
sions starts with partnership with suppliers one British emission coefficient that did
and understanding the sustainability of not incorporate more modern manufac-
supply chains and product lifecycles. A turing or consider the procured materials
recent survey found that many of the re-use used in Wellington. Here a product life-
and recycling practises of India would be cycle analysis of surgical supplies was not
acceptable to American surgeons if cost and possible, but it would form an important
safety were maintained.13,17 There is a strong part of future research. Likewise, a more
appetite for more sustainable, less wasteful granular approach to measuring patient and
surgery, but cataract surgeons, at least in staff behaviour will help motivate change,
the United States (US), feel a lack of agency.17 such as by capturing variations in the use
As well as industry, agencies that regulate of consumables or travel and follow-up
doctors and hospitals are seen to represent patterns.
barriers to change and barriers to avenues Another weakness is the possibility of
for effecting change. In New Zealand, PHAR- selection bias due to the incomplete sample
MAC’s upcoming role in bulk-purchasing of cataract surgeries performed during
surgical supplies represents a major oppor- the study period. We quickly reached
tunity both to improve measurement of 40 cases from private hospitals without
emissions related to procurement and to sampling cases from all surgeons, whereas
leverage reductions in emissions during at Wellington Regional Hospital (one of the
contract negotiations. public hospitals in our sample) we could
Large hospitals, as major employers and not reach 40 cases in the time available,
the destination for thousands of people despite including nearly every cataract
every day, could improve the sustainability operation. Our methods did not detect any
of transport systems by targeting reductions substantial differences between surgeons,
in their own transport emissions. Innovative and so although the non-random sampling
approaches include partnerships with local of operations could lead to a non-repre-
government to further subsidise public sentative sample, we do not think this led
transport for patients and employees (eg, the to systematic errors in our estimations of
Business EcoPass initiative in Boulder County, emissions.
Colorado, US). Hospitals could also provide To conclude, this study has created a
facilities and advocate for better and safer starting point for improving the sustain-
active transport (eg, cycling and walking).18 ability of cataract surgery in New Zealand
Active transport also improves health in and offers a benchmark for comparison
the community by increasing physical with other hospital systems. Improved
activity, reducing air pollution and injury methods will be needed to accurately
and improving mental health.18,19 Reducing measure how surgical products affect
demand for healthcare through better popu- carbon footprints. Our results highlight
lation health is one of the key principles of a how working with industry suppliers is
low-carbon healthcare system.5 perhaps the most effective first step. Central
In December 2020, the New Zealand government policy will create high-level
Government announced that the public and top-down changes, but changes in the
sector will become carbon neutral by behaviour of individual surgeons will also
2025.10 The public hospital systems within be required. Due to its high volume, cataract
district health boards were to be included surgery is a good early target for meaning-
in principle with further announcements fully reducing emissions in New Zealand’s
of their dates of inclusion in the year to healthcare system.
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Competing interests:
Nil.
Acknowledgements:
The authors gratefully acknowledge the participation and support of numerous organisa-
tional leaders and staff in Capital & Coast District Health Board, Hutt Valley District Health
Board, Boulcott Hospital, Bowen Hospital and Southern Cross Hospital Wellington. Dr Peter
Thomas of Moorfields Eye Hospital, London, co-founder of the Eyefficiency project, kindly
supported and facilitated our study.
Author information:
Matthew Latta: Medical Student, Department of Surgery & Anaesthesia,
University of Otago Wellington, Wellington.
Caroline Shaw: MB ChB PhD FNZCPHM, Academic Public Health Physician,
Department of Public Health, University of Otago Wellington, Wellington.
Jesse Gale: MB ChB FRANZCO, Ophthalmologist, Department of Surgery & Anaesthesia,
University of Otago Wellington, Wellington.
Corresponding author:
Dr Jesse Gale, Eye Clinic, Wellington Hospital, Private Bag 7902, Wellington South 6242
jesse.gale@otago.ac.nz
URL:
www.nzma.org.nz/journal-articles/the-carbon-footprint-of-cataract-surgery-in-wellington
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