Desflurane Concentrations and Consumptions during
Low Flow Anesthesia
Ruenreong Leelanukrom MD*, Lawan Tuchinda MD*,
Paweena Jiamvorakul MD*, Alisara Koomwong MD*
Affiliation :
* Department of Anesthesiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
Background : Desflurane is the least soluble and most expensive inhalation agent. Hence, low flow technique is suitable
for anesthesia with desflurane. However, one of the disadvantages of low flow technique is the discrepancy among the
end-tidal concentration, inspired concentration, and vaporizer setting.
Objective : To measure the concentrations of desflurane at different sites of the anesthesia circuit by varying fresh gas flow
(FGF) rates but fixing expired concentration.
Material and Method: Thirty ASA PS I-II adult patients were enrolled in this crossover study. After induction of anesthesia
and ten minutes of wash-in period, the flow meters of oxygen and air were then adjusted to maintain FiO2 at 0.3 with the
random sequences of FGF rates at 0.5, 1 and 2 L.min-1. Desflurane vaporizer was adjusted to obtain 5% end-tidal desflurane
concentration (FeDES) throughout the study period. After FeDES reached the target and was stable for 20 minutes, inspired
concentration of desflurane (FiDES) and delivered desflurane concentration at fresh gas outlet (FdDES) were measured.
Lastly, the consumption of desflurane was calculated.
Results : FdDES was higher than FiDES in every FGF rates. FdDES at FGF 0.5 L.min-1 (6.130.12) was significantly higher
than FdDES at 1 and 2 L.min-1 (5.680.08, 5.540.07, respectively), but not significantly different between FGF 1 and
2 L.min-1. FeDES/FdDES at FGF 0.5, 1 and 2 L.min-1 were 0.820.014, 0.880.012 and 0.870.011, respectively. There
was no significant difference of FeDES/FdDES between FGF 1 and 2 L.min-1, but there was significant difference between
FGF 1 and 0.5 L.min-1 with the p-value <0.001. The calculated liquid desflurane consumption per hour at FGF rate of
0.5, 1 and 2 L.min-1 were 8.770.17, 16.280.24 and 31.730.41 mL.hr-1.
Conclusion : Using FGF 2 L.min-1 has no advantage over FGF 1 L.min-1, because they both have the similar FdDES.
Regarding at FGF 0.5 and 1 L.min-1, the delivered concentration has to be increased to obtain the desired expired concentration
with more intense at FGF 0.5 L.min-1 because there are more discrepancies between FdDES and FeDES.
Keywords : Low flow anesthesia, Desflurane, Concentration, Consumption
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