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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