Greenhouse Gas Emissions of Sevoflurane Outweigh Those of Carrier Gas and Carbon Dioxide Absorbers across the Fresh Gas Flow Spectrum.

BACKGROUND

The absolute and relative effects of lowering fresh gas flows (FGFs) on the carbon dioxide equivalent (CO 2 e) emissions of sevoflurane, carrier gases (oxygen/air) and prepacked carbon dioxide canister remain poorly quantified. The authors quantified these factors across a 0.2 to 4-l/min FGF range during the first hour of anesthesia.

METHODS

Data were compiled from three studies including 132 American Society of Anesthesiologists (Schaumburg, Illinois) Physical Status I to III patients receiving a constant end-tidal sevoflurane concentration (FETsevo) using manual (n = 50) or target-controlled delivery (n = 48) with 0.2 to 4 l/min FGF or during automated closed-circuit delivery (n = 34). Sevoflurane consumption was normalized to both 1.3 and 2.0% FETsevo, and carrier gas use to an inspired oxygen concentration of 30% and 60%. Prepacked carbon dioxide absorbent usage was calculated using a previously described model for both 130 and 160 ml/min carbon dioxide output ( ). Published CO 2 e values were used to derive CO 2 e of sevoflurane.

RESULTS

Sevoflurane CO 2 e increases linearly with FGF (range, 2.4 to 18.6 kg CO 2 e), except when a brief wash-in period was used due to low FGF (FGF less than 1 l/min). Carrier gas CO 2 e decreases with lower FGF but in a more complex manner, and increases with higher inspired oxygen concentration (range, 0.010 to 0.124 kg CO 2 e). Absorbent CO 2 e decreases linearly with FGF (range, 0 to 0.070 kg CO 2 e). The CO 2 e of sevoflurane is two orders of magnitude higher than CO 2 e of carrier gas and carbon dioxide absorbent, which are similar.

CONCLUSIONS

When delivering sevoflurane in oxygen/air, the CO 2 e contribution of the carrier gas and carbon dioxide absorbent is less than 3%, even during closed-circuit delivery. While CO 2 e is only one element of a comprehensive life cycle analysis, the presented CO 2 e data underscore that the key to minimizing the global warming potential of sevoflurane is lowering FGF and decreasing FETsevo.