Total carbon dioxide equivalents per induction for cases where halogenated agents and/or nitrous oxide was administered during the induction period of anesthesia

Inhalational agents (halogenated hydrocarbons and nitrous oxide) leaking or vented into the atmosphere are environmental pollutants.  Reducing emissions can decrease public health harm and cost of anesthesia without compromising patient care. ^1–13

“Global Warming Potential (GWP) is a measure of how much a given mass of greenhouse gas contributes to global warming over a specified period of time. The Intergovernmental Panel on Climate Change uses 100 years; however, 20, 50, 500 years are common as well, depending on the gas in question. GWP is a relative scale that compares the contribution of the gas in question to that of the same mass of carbon dioxide. The GWP of carbon dioxide, by definition, is one.”² 

Induction Start to Induction End

Cases where halogenated hydrocarbons and/or nitrous oxide were administered during induction

• Cases in which halogenated hydrocarbons or nitrous oxide are NOT used for induction
• Cases with only manually entered fresh gas flow values (fresh gas flow values must be automated to be considered for this measure)

Carbon dioxide equivalents will be reported as kilograms of carbon dioxide equivalents per case

Emissions data are also converted to other meaningful equivalencies & reported as:

• Miles driven by an average gasoline-powered passenger vehicle
• Gallons of gasoline consumed

Inhalational agents and flows will be assessed and considered as artifact if inside the ranges listed within the Halogenated Anesthetic Gases and Nitrous Oxide Used phenotypes. See Appendix for how minutes are included before calculating kg CO₂ equivalents.

*This measure will include valid MPOG cases defined by the Is Valid Case phenotype.

Calculations:

Site Average kg CO₂  =  SUM ('Total CO2 Equivalents') / COUNT Included cases (Institution only)

MPOG Average kg CO₂  =  SUM ('Total CO2 Equivalents') / COUNT Included cases (All MPOG)

Total Minutes Included  =  SUM (minutes within measure bounds, with both halogenated agent and flows present)

Average kg CO₂/min  =  SUM ('Total CO2 Equivalents') / SUM ('Total Included Minutes')

Total CO₂ equivalents is calculated by determining the pollutant total for the time period and dividing by the total number of minutes between induction start and induction end:

Pollutant Total: [Inspired agent concentration (%) * fresh gas flow (l/min)] * GWP₁₀₀

1. Calculate CO₂ eq for each minute of Sevoflurane %, Isoflurane and Desflurane %  *
2. Calculate CO₂ eq for each minute of Nitrous Oxide % or Nitrous Oxide flows **
3. Sum CO₂ equivalents 
4. Divide by total included minutes: Total CO₂ eq/Total # of minutes
   • Included Minute = minute within measure bounds, with both halogenated agent and flows present

* CO₂ eq for Sevoflurane, Isoflurane or Desflurane (%):

1. Convert agent % → mLs of agent/min: (FGF (l/min) x 1,000 x agent %) / 100 
2. Convert mls/min → moles:  agent mL / 24,400
   • The Editors of Encyclopedia Britannic
3. Convert moles → mass: (agent moles x MW of agent) / 1,000
4. Convert mass → CO₂ equivalents: agent mass x GWP of agent 

** CO₂ eq For Nitrous Oxide:

For cases with documented Nitrous Oxide % but Nitrous Oxide flow is not reported, then use Nitrous Oxide % and FGF:

• Divide Nitrous Oxide % / 100 = N
• Convert N → mLs/min: (FGF (l/min) x 1,000 x N) 
• Convert mls/min → moles:  N mL / 24,400
• Convert moles → mass: (N moles x MW of agent) / 1,000
• Convert mass → CO₂ equivalents: N mass x GWP of agent

For cases with both valid Nitrous Oxide % and Nitrous Oxide flows reported, only Nitrous Oxide flows will be considered (N2O values reported as % will be ignored):

1. Convert Nitrous Oxide (l/min) → mols/min: Nitrous Oxide  / 24.4 = Nmol
2. Convert Nmol → N20 mass (kg/min): (Nmol *44) / 1,000 
3. Convert Nmass → CO₂ equivalents: Nmass * GWP 

From Greening the Operating Room and Perioperative Arena: Environmental Sustainability for Anesthesia Practice:

“Global Warming Potential (GWP) is a measure of how much a given mass of greenhouse gas contributes to global warming over a specified period of time. The Intergovernmental Panel on Climate Change uses 100 years; however, 20, 50, 500 years are common as well, depending on the gas in question. GWP is a relative scale that compares the contribution of the gas in question to that of the same mass of carbon dioxide. The GWP of carbon dioxide, by definition, is one.”(Greening the Operating Room )

Table adapted from American Society of Anesthesiologists’ Task Force on Environmental Sustainability Committee on Equipment and Facilities: Greening the Operating Room and Perioperative Arena: Environmental Sustainability for Anesthesia Practice^{(?Greening the Operating Room )}

*Nitrous oxide value is derived as an average of the range provided on the EPA website: 265-298.

Calculations for equivalencies:

Miles driven by an average gasoline-powered passenger vehicle (per EPA.gov): 

1. Convert kg CO2 equivalents -> metric tons: Total kg CO2/1000
2. Convert metric tons CO2 eq. -> miles driven: Metric tons CO2 eq. / (0.000403)

*Methodology for determining conversion factor (0.000403): 

8.89 × 10-3 metric tons CO2/gallon gasoline × 1/22.2 miles per gallon car/truck average × 1 CO2, CH4, and N2O/0.994 CO2 = 4.03 x 10-4 metric tons CO2E/mile

Gallons of gasoline (per EPA.gov):

1. Convert kg CO2 equivalents -> grams of CO2 equivalents: Total kg CO2*1000
2. Convert grams CO2 eq. -> gallons of gasoline: grams CO2 eq./8,887

*Rationale for applying conversion factor 8,887g CO2 eq/gallon of gasoline:

‘In the preamble to the joint EPA/Department of Transportation rulemaking on May 7, 2010 that established the initial National Program fuel economy standards for model years 2012-2016, the agencies stated that they had agreed to use a common conversion factor of 8,887 grams of CO2 emissions per gallon of gasoline consumed (Federal Register 2010)’

Not applicable

Departmental only measure - not available for provider feedback emails.

1. The Editors of Encyclopedia Britannica: mole 2020 at <https://www.britannica.com/science/mole-chemistry>
2. Greening the Operating Room at <https://www.asahq.org/about-asa/governance-and-committees/asa-committees/environmental-sustainability/greening-the-operating-room>
3. Epa US, OAR: Understanding global warming potentials 2016 at <https://www.epa.gov/ghgemissions/understanding-global-warming-potentials>
4. Hodnebrog Ø, Aamaas B, Fuglestvedt JS, Marston G, Myhre G, Nielsen CJ, Sandstad M, Shine KP, Wallington TJ: Updated Global Warming Potentials and Radiative Efficiencies of Halocarbons and Other Weak Atmospheric Absorbers. Rev Geophys 2020; 58:e2019RG000691
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7. Hendrickx JF: The pharmacokinetics of inhaled anesthetics and carrier gases. Belgium: Ghent University 2004
8. Lowe HJ, Ernst EA: The Quantitative Practice of Anesthesia: Use of Closed Circuit. Williams & Wilkins, 1981
9. Barwise JA, Lancaster LJ, Michaels D, Pope JE, Berry JM: An Initial Evaluation of a Novel Anesthetic Scavenging Interface. Anesthesia & Analgesia 2011; 113:1064
10. Tjus MEA: Destruction of Medical N2O in Sweden doi:10.5772/32169
11. Eisenkraft JB, McGregor DG: Waste Anesthetic Gases and Scavenging Systems 2013:pp 125–47 doi:10.1016/b978-0-323-11237-6.00005-4
12. Feldman JM: Managing fresh gas flow to reduce environmental contamination. Anesth Analg 2012; 114:1093–101
13. McGain F, Muret J, Lawson C, Sherman JD: Environmental sustainability in anaesthesia and critical care. Br J Anaesth 2020; 125:680–92