Calculating Global Warming
Footprint from Inhaled Anesthetics
MPOG Sustainability Measures
Reducing Environmental Impact of Anesthesia
All inhaled anesthetics agents have a global warming potential significantly
greater than that of carbon dioxide.
These gases are potent contributors to global warming, even in small
concentrations.
We can reduce this impact in two primary ways:
1. Selecting environmentally-safer anesthetic agents
2. Managing our total fresh gas flows
MPOG Sustainability Measures
● SUS-01: Fresh Gas Flow, less than or equal to 3L/min
● SUS-02: Global Warming Footprint, Maintenance
● SUS-03: Global Warming Footprint, Induction
● SUS-04: Fresh Gas Flow, less than or equal to 2L/min
● SUS-05-Peds: Nitrous Avoided, Induction
● SUS-06-Peds: Low Fresh Gas Flow, Pediatric Induction
● SUS-07: Nitrous Oxide Avoided
Fresh Gas Flow
Agent Choice
CO2 eq
SUS-02
SUS-03
SUS-05: Pediatric
Nitrous Use
SUS-07: Adult
Nitrous Use
SUS-01: < 3L/min
SUS-04: < 2L/min
SUS-06:
Pediatric
Weight-based
Flows
MPOG Sustainability Measures
MPOG Sustainability Measure Time Periods
Measure Start Measure End
SUS-01
Intubation Extubation End
SUS-02
Intubation Extubation End
SUS-03
Intubation Induction End
SUS-04
Intubation Extubation End
SUS-05-Peds
Induction Start Intubation. If none, Induction End
SUS-06-Peds
Induction Start Intubation. If none, Induction End
SUS-07
Anesthesia Start Anesthesia End
Minimizing Fresh Gas Flow
SUS-01
● Percentage of cases with mean fresh gas flow (FGF) ≤ 3L/min, during
administration of halogenated hydrocarbons and/or nitrous oxide.
SUS-04
● Percentage of cases with mean fresh gas flow (FGF) ≤ 2L/min, during
administration of halogenated hydrocarbons and/or nitrous oxide.
*FGF measures do not consider agent choice – great starting place for sites to begin
working on sustainability.
Measures that focus on Fresh Gas Flow*
Minimizing Fresh Gas Flows during Maintenance of Anesthesia
Maintenance is defined as:
● Measure Start:
○ Intubation. If not available, then
○ Induction End.
● Measure End
○ Extubation Time. If not available, then
○ LMA Removal Time. If not available, then
○ Surgery End. If not available, then
○ Patient Out of Room. If not available,
then
○ Anesthesia End
.
Flow and gas values are considered
artifact
if inside the following ranges:
● Nitrous Oxide Flows: < 0.2 L/min
● Isoflurane Insp: < 0.3%
● Sevoflurane Insp: < 0.4%
● Desflurane Insp: < 1.2%
● Nitrous Oxide Insp: < 20%
Step 1: Determine which minutes to include in the measure. Included minutes must
meet all of the following criteria (see next slide for graphical representation):
A. Within the measure time bounds
● Measure start (Induction start time)
● Measure end (Patient Extubated)
B. Valid (non-artifact) Fresh Gas Flow value documented
● Air, Oxygen, Nitrous Oxide (L/min)
C. Valid (non-artifact) Inhaled Agent value documented
● Sevoflurane, Isoflurane, Desflurane, Nitrous Oxide
Calculating Mean Fresh Gas Flow (SUS-0 1 & SU S-04)
Included Minute: All three criteria must align
EXAMPLE CASE
*Copied and pasted minute to minute gas and flows from Case Viewer into Excel.
*Does not assess gas choice.
Step 2: Sum the gas flows to obtain the total fresh gas flow for
each minute.
Nitrous Oxide (L/min) + Oxygen (L/min) + Air (L/min) = Total Fresh Gas Flow
Steps 3 & 4: Calculate the average FGF
Step 3: Sum the total fresh gas flow
for each minute
Step 4: Divide the total by the
number of included minutes (65)
For this case:
● Average gas flow of 2.08 for
this case. What happened?
● At end of case, Oxygen flows
were 14.9 L/min + Nitrous Oxide
flows at 1 L/min = 15.9 L/min
for a single minute of the case.
*This case passed SUS-01 but
flagged SUS-04.
SUS-0 1 an d SU S-04 Calculations Overview
● Determine measure time period:
○ Measure start (Induction start time): 1051 → Measure end(Patient Extubated): 1156
○ Measure time period = 65 minutes
● Determine which minutes to include: 62
○ SUS 01, 04 - Fresh Gas Flow (O
2
, Air, N
2
O) running
● Sum of total flows for each included minute
● Take the average of the flows for the included minute
○ Add up flows for all included minutes and divide by the total number of include
minutes.
○ Average is used instead of median to account for minutes of high flows during the case
and to get an average of flow use per case..
SUS-06-Peds: Low Fresh Gas Flow, Pediatric Induction
● Percentage of pediatric patients with a mean fresh gas flow (FGF) less than or
equal to established weight-based threshold during induction.
● Weight-based thresholds based on Society for Pediatric Anesthesia (SPA)
Recommendations:
Weight (kg) Mean FGF
< 20 <
3 L/min
20 - 30 <
4 L/min
30 - 40 <
5 L/min
> 40 <
6 L/min
Global Warming Footprint
(SUS-02 & SUS-03)
SUS-02: Global Warming Footprint (Maintenance)
Percentage of cases where carbon dioxide equivalents (CO
2
eq) normalized by hour for
cases receiving halogenated agents and/or nitrous oxide is:
Less than CO
2
eq of 2% sevoflurane at 2L FGF = 2.83kg CO
2
/hr
or
Total CO
2
eq is less than 2.83kg CO
2
…for the maintenance period of anesthesia.
Maintenance period of Anesthesia for SUS-02
Maintenance is defined as:
● Measure Start:
○ Intubation. If not available, then
○ Induction End.
● Measure End
○ Extubation Time. If not available, then
○ LMA Removal Time. If not available, then
○ Surgery End. If not available, then
○ Patient Out of Room. If not available,
then
○ Anesthesia End
.
Of Note: Flow and gas values are
considered artifact if inside the following
ranges:
● Nitrous Oxide Flows: < 0.2 L/min
● Isoflurane Insp: < 0.3%
● Sevoflurane Insp: < 0.4%
● Desflurane Insp: < 1.2%
● Nitrous Oxide Insp: < 20%
Step 1: Calculating Fresh Gas Flow for SUS-02
● Determine included minutes for the measure where FGF values and Inhaled
agent values are documented within the bounds of the measure time period
● Sum the gas flows to obtain total FGF for each minute
Step 2: Calculate CO2 eq for each inhaled agent for each minute.
*If multiple agents are running for a single minute, calculate the CO
2
for each agent, then add CO
2
eq . fr o m
each agent together to calculate total CO
2
eq for the minute.
Sevo/Iso/Desflurane: Calculation & Reference Table
SUS-02 Example Case: Calculate CO2 eq. for each minute
Sevoflurane + Nitrous Oxide running
Sevoflurane CO
2
equivalents:
1) Convert % agent → mLs of agent:
(3*1,000*1.8 )/100 = 54
1) Convert mLs/min to moles: 54/24,400 = 0.002213
2) Convert moles to mass: (0.002213 * 200) / 1,000 = 4.43 * 10
-4
3) Convert mass to CO
2
eq: 4.43x10
-4
* 144 = 0.0637
Nitrous Oxide: Calculation and Reference Table
Example: Calculate CO2 eq of Nitrous Oxide
Since Nitrous Oxide is reported as flows (L/min), use second equation (steps 1-3) for
calculation:
1144: Nitrous oxide flow was 0.8 L/min
1. 0.8 / 24.4 = 0.0328
2. (0.0328 * 44) / 1,000 = 0.0014432
3. 0.014432 * 282 = 0.407 CO
2
eq
Example: Nitrous Oxide calculation if reported as Insp %
(instead of L/min)
Nitrous Oxide Insp %: 35.2%
● 35.2 / 100 = 0.352
● 2.2 * 1000 * 0.352 = 774.4
● 774.4 / 24,400 = 0.0317377049
● (0.0317377049 * 44) / 100 = 0.0139645902
● 0.0139645902 * 282 = 3.938 CO
2
eq
Step 3: Determining Mean CO
2
eq per hour for the case
(reported as kg CO
2
/hr)
1. Calculate CO
2
eq for each included minute of
Sevoflurane% /Desflurane %/Isoflurane %
2. Calculate CO
2
eq for each included minute of Nitrous
Oxide % or Nitrous Oxide Flows (L/min)
3. Sum CO
2
eq
4. Divide by total of included minutes:
a. Total CO2 eq / Total # minutes = CO2 eq/min
5. Multiple Total CO
2
eq/min X 60 = Mean CO
2
eq/hr
1. Total CO
2
eq for Sevoflurane % = 2.598846451
2. Total CO
2
eq for Nitrous Oxide (L/min) = 5.390360656
3. 2.598846451 + 5.390360656 = 7.989207107
4. 7.989207107 / 62 = 0.128858179
5. 0.128858179 * 60 = 7.731490749
MEAN CO
2
eq/hr for case = 7.731 ….FLAG
SUS-02 Threshold = Mean CO
2
of 2.83kg CO
2
*Total CO2 eq is calculated by determining the pollutant total for the time period and dividing by total minutes between Intubation and Extubation Time.
Carbon dioxide equivalents for each inhaled agent:
FGF constant at 2L/min
Agent used % Insp FGF CO
2
eq./minute
Sevoflurane 2% 2 L/min 0.047
Isoflurane 1% 2 L/min 0.085
Desflurane 6% 2 L/min 2.111
Nitrous Oxide 50% 2 L/min 0.509
SUS-03: Global Warming Footprint, Induction
Total carbon dioxide equivalents per induction for cases where halogenated agents
and/or nitrous oxide was administered during the induction period of anesthesia.
Total CO
2 equivalents is calculated by determining the pollutant total for the time
period and dividing by the total number of minutes between the induction period.
Induction period: Induction Start
to Induction End
SUS-03: Calculations
● Follows the same steps as SUS-02, but with a shorter measure time period being
between Induction Start to Induction End
● Additional calculations for this measure:
○ Site average kg CO
2
= SUM (‘Total CO
2
eq) / COUNT included cases
○ Average kg CO
2
/min = SUM (‘Total CO
2
eq) / SUM (‘Total Included Minutes’)
*There is no threshold for this measure.
Agent Considerations:
Avoiding Nitrous Oxide
(SUS-05 & SUS-07)
SUS-05-Peds: Nitrous Avoided, Induction
● Percentage of pediatric patients where nitrous oxide was avoided
● Nitrous oxide values will be assessed and considered artifact within the following
ranges:
○ Nitrous Oxide Flows: < 0.2 L/min
○ Nitrous Oxide Insp %: < 20%
● Reducing nitrous oxide use will also decrease total carbon dioxide emissions for
the case.
SUS-07: Nitrous Oxide Avoidance - Adults
● Percentage of adult cases where nitrous oxide is avoided during anesthesia.
● Nitrous oxide values will be assessed and considered artifact within the
following ranges:
○ Nitrous Oxide Flows: < 0.2 L/min
○ Nitrous Oxide Insp %: < 20%
● Reducing nitrous oxide use will also decrease total carbon dioxide emissions for
the case.
Measure Overview
Measure Start: Measure End: Calculate Fresh
Gas Flow
Calculate CO
2
Assesses Agent(s)
Used
SUS-01
Intubation Extubation End
√
SUS-02
Intubation Extubation End
√ √
SUS-03
Intubation Induction End
√ √
SUS-04
Intubation Extubation End
√
SUS-05-Peds
Induction Start Intubation
√
SUS-06-Peds
Induction Start Intubation
√
SUS-07
Anesthesia
Start
Anesthesia End
√
Questions or Light Bulb moment?
