Low-flow anaesthesia with a fixed fresh gas flow rate

Abstract

During the wash-in period in low flow anaesthesia (LFA), high fresh gas flow is used to achieve the desired agent concentration. In this study, we aimed to evaluate the safety of fixed 1 L/min fresh gas flow desflurane anaesthesia in both the wash-in and maintenance periods in patients including the obese ones. 104 patients undergoing surgery under general anaesthesia were included. After endotracheal intubation, fresh gas flow was reduced to 1 L/min and the desflurane vaporizer was set at 18%. The time from opening the vaporizer to end-tidal desflurane concentration reaching 0.7 MAC was recorded (MAC 0.7 time). Throughout the surgery, hemodynamic variables, FIO2, MAC and BIS values were observed. MAC 0.7 time, BIS and MAC values at the start of surgery, number of adjustments in vaporizer settings, desflurane consumption were recorded. The average MAC 0.7 time was 2.9 ± 0.5 min. MAC and BIS values at the start of the surgery were 0.7 (0.6–0.8) and 39 ± 8.5 respectively. No individual patient had a BIS value above 60 throughout the surgery. Hemodynamic variables were stable and FIO2 did not fall below 30% in any patient. The number of adjustments in vaporizer settings was 56. Average desflurane consumption was 0.33 ± 0.05 mL/min. We demonstrated that LFA without use of initial high fresh gas flow during the wash-in period is an effective, safe and economic method which is easy to perform.

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