Anesth Pain Med.  2020 Oct;15(4):434-440. 10.17085/apm.20055.

Change of inspired oxygen concentration in low flow anesthesia

• Kim J
• Kang D
• Lee H
• Ryu S
• Ryu S
• Kim D

• KMID: 2508405
• DOI: http://doi.org/10.17085/apm.20055

Abstract

Background
There are several advantages of low flow anesthesia including safety, economics, and eco-friendliness. However, oxygen concentration of fresh gas flow and inspired gas are large different in low flow anesthesia. This is a hurdle to access to low flow anesthesia. In this study, we aimed to investigate the change in inhaled oxygen concentration in low flow anesthesia using oxygen and medical air.
Methods
A total of 60 patients scheduled for elective surgery with an American Society of Anesthesiologist physical status I or II were enrolled and randomly allocated into two groups. Group H: Fresh gas flow rate (FGF) 4 L/min (FiO₂ 0.5). Group L: FGF 1 L/min (FiO₂ 0.5). FGF was applied 4 L/min in initial phase (10 min) after intubation. After initial phase FGF was adjusted according to groups. FGF continued at the end of surgery. Oxygen and inhalation anesthetic gas concentration were recorded for 180 min at 15 min interval.
Results
The inspired oxygen concentration decreased by 5.5% during the first 15 min in the group L. Inspired oxygen decreased by 1.5% during next 15 min. Inspired oxygen decreased by 1.4% for 30 to 60 min. The inspired oxygen of group L is 35.4 ± 4.0% in 180 min. The group H had little difference in inspired oxygen concentration over time and decreased by 1.8% for 180 min.
Conclusions
The inspired oxygen concentration is maintained at 30% or more for 180 min in patients under 90 kg. Despite some technical difficulties, low flow anesthesia may be considered.

Keyword

Balanced anesthesia; General anesthesia; Inspired oxygen; Low flow

Figure

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  Fig. 1. Changes in inspired (A) and expired (B) oxygen concentration over time in both group. Data represents mean ± SD. Group H = fresh gas flow 4 L/min, FiO2 0.5, O2 1.5 L/min, Air 2.5 L/min; Group L = fresh gas flow 1 L/min, FiO2 0.5, O2 0.37 L/min, Air 0.63 L/min.

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  Fig. 2. Changes in inspired desflurane (A) and sevoflurane (B) concentration over time in both group. Data represents mean ± SD. Group L = fresh gas flow 1 L/min, FiO2 0.5, O2 0.37 L/min, Air 0.63 L/min; Group H = fresh gas flow 4 L/min, FiO2 0.5, O2 1.5 L/min, Air 2.5 L/min.

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  Fig. 3. Changes in esophageal body temperature (BT) over time in both group. Data represents mean ± SD. Group L = fresh gas flow 1 L/min, FiO2 0.5, O2 0.37 L/min, Air 0.63 L/min; Group H = fresh gas flow 4 L/min, FiO2 0.5, O2 1.5 L/min, Air 2.5 L/min.

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  Fig. 4. Correlation between inspired oxygen concentration and body weight in 60 min (A), 120 min (B). Group H = fresh gas flow 4 L/min, FiO2 0.5, O2 1.5 L/min, Air 2.5 L/min; Group L = fresh gas flow 1 L/min, FiO2 0.5, O2 0.37 L/min, Air 0.63 L/min.

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