Percentage of cases with mean fresh gas flow (FGF) less than or equal to 1L/min for the administration of inhaled anesthetics and/or nitrous oxide during the maintenance phase of anesthesia.

Halogenated agents and nitrous oxide leaking or vented into the atmosphere are environmental pollutants.  Reducing fresh gas flows can reduce cost of anesthesia without compromising patient care. This measure considers Fresh Gas Flow (FGF) during administration of halogenated hydrocarbons and/or nitrous oxide, as an indirect measure of anesthetic gas waste.

Intubation to Extubation

Patients with an ETT/LMA (determined by Anesthesia Technique: General value codes: 1, 2, 3, 6) 

• ASA 5 & 6 exclusion including Organ Procurement (CPT:01990) 
• Cases without ETT/LMA placed (determined by Anesthesia Technique: General value codes: 0, 4, 5) 
• Cases without halogenated hydrocarbons or nitrous oxide administration 
• Case with < 30 minutes of halogenated hydrocarbons and/or nitrous oxide administered between intubation and extubation 
• Cases with documentation of Nitric Oxide use 
• Cases with only manually entered fresh gas flow values (fresh gas flow values must be automated to be considered for this measure) 

Mean FGF < 1 L/min when inspired halogenated hydrocarbons is > 0.2%, or nitrous oxide FGF > 0.2 L/min, during the maintenance period of anesthesia.

Measure Start:  

1. Intubation. If not available, then  
2. Induction End  

Measure End:  

1. Latest Extubation Time. If not available, then  
2. Latest LMA Removal Time. If not available, then  
3. Surgery End. If not available  
4. Patient Out of Room. If not available, then  
5. Anesthesia End.  

• If Fresh Gas Flow Total (MPOG Concept ID: 3214) is documented for the case, this concept will be used to determine success in the setting of halogenated agents or nitrous oxide use.  
• If Fresh Gas Flow Total (MPOG Concept ID: 3214) is not documented for the case, MPOG will calculate Fresh Gas Flow: Flows Oxygen (ID: 3215) + Flows Air (ID: 3220) + Flows Nitrous Oxide (ID: 3225)  
• There must be at least 3 consecutive minutes of FGF and agents, and at least 30 minutes of FGF and agents aligned for a case to be included.  
• There must be at least 30 minutes of non-artifact Nitrous Oxide or inspired halogenated hydrocarbons during the maintenance period. Maintenance period is defined as measure start to measure end. See Appendix for how minutes are included before calculating mean fresh gas flow. When calculating the mean Fresh Gas Flow, the sum of all flows will be added and divided by the total number of minutes that have a documented gas flow. If there are 30 cumulative minutes of halogenated gas documented, but only 24 minutes of fresh gas flow, the mean will be calculated using the 24 minutes of fresh gas flow.    
• Of the total number of minutes of gas flows documented, at least 80% of the Fresh Gas Flow values must be machine data captured for the case to be included. Any manually entered fresh gas flow or agent values will be included in the calculation of mean FGF if this threshold is met and the case is included.  
• If there is a gap in documentation for fresh gas flow values, each value is valid for up to one minute.  
• If multiple flow values for oxygen (3215), air (3220), and Nitrous Oxide (3225) occur at different second intervals in the same minute, all values will be aligned to the beginning of the minute and the one documented first will be used. For example, if 1 L/min of oxygen flow was documented at 13:02:30 and 2 L/min of air flow was documented at 13:02:32, both would be assigned 13:02 as the documented time and the total FGF would equal 3 L/min for that minute.  
• Artifact values are determined by the Anesthetic Gases Reference Table Phenotype

** Calculating CO2 eq For Nitrous Oxide:  

For cases with only Nitrous Oxide reported as inspired (%), convert Nitrous Oxide (N2O) reported as inspired (%) to L/min: (If reported as L/min, skip to CO2 equivalent calculation below).  

1. If not available. MPOG will determine percentage inspired for Oxygen by subtracting Nitrous Oxide percent inspired value from 100.  
2. Calculate the total Fresh Gas Flow by dividing Oxygen flows (L/min) by Oxygen percent. 
3. Calculate Nitrous flow by subtracting Oxygen flows (L/min) form total Fresh Gas Flow.  

Please note: In rare cases where both nitrous oxide and air are delivered, MPOG adjusts these steps to include both air and oxygen in these steps (instead of just oxygen alone).  

CO2 Equivalent Calculation (N2O):  

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   

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

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

Not applicable

Provider(s) signed in for at least 30 minutes during the time when halogenated agent or nitrous oxide are documented.

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Next Review: 2028

Published date: 07/2025