Thursday, October 25, 2012

The clinical use inhaled anesthetics and CO2 emissions.


The clinical use inhaled anesthetics and CO2 emissions.
Alisher I. Agzamov, AbdulRaheem Al Qattan.
Department of Anesthesiology & ICU, Al Sabah & Zain Hospitals, MOH, Kuwait City, Kuwait.
BACKGROUND: The inhaled anesthetics are recognized greenhouse gases. Calculating their impact during clinical usage will allow comparison to each other and to CO2 emissions.
METHODS: We determined infrared absorption cross-sections for desflurane, sevoflurane and isoflurane. 20 years global warming potential (GWP(20)) values for desflurane, sevoflurane, and isoflurane were then calculated using the present infrared results, and best estimate atmospheric lifetimes were determined. Used in 1 (MAC)-hour  agents was then multiplied by the calculated GWP(20) for that anesthetic, and expressed as " CO2 equivalent" (CDE(20)) in grams. Common fresh gas flows and carrier gases, both Air/O2 and N2O/O2, were considered in the calculations to allow clinical use of inhaled anesthetics.
RESULTS: GWP(20) values were: sevoflurane 348, isoflurane 1402, and desflurane 3715. CDE(20) values: sevoflurane 6981 g, isoflurane 15,6 g, and desflurane 188,2 g. Comparison among these anesthetics produced a ratio of sevoflurane 1, isoflurane 3, and desflurane 27. When 50% N2O/50% O2 replaced Air/O2 as a gas combination, and agents delivery was adjusted to deliver 1 MAC-hour of anesthetic, sevoflurane CDE(20) values were 6.1 times higher with N2O than when carried with air/O2, isoflurane values were 3.0 times higher, and desflurane values were 0.45 times lower. On a 100-year time horizon with 50% N2O, the sevoflurane CDE(100) values were 20 times higher than when carried in air/O2, isoflurane values were 10 times higher, and desflurane values were equal with and without N2O.
CONCLUSIONS: Desflurane has a potential impact on global warming than isoflurane or sevoflurane. N2O produces a greenhouse gas contribution relative to sevoflurane or isoflurane. 50% N2O combined with inhaled anesthetics increases the environmental impact of sevoflurane and isoflurane, and decreases that of desflurane. N2O is destructive to the ozone layer as well as possessing GWP; it continues to have impact over a longer timeframe, and may not be an environmentally sound tradeoff for desflurane. Our study shows that avoiding N2O and unnecessarily high fresh gas flow rates can reduce the environmental impact of inhaled anesthetics.


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