The impact of fresh gas flow on wash-in, wash-out time and gas consumption for sevoflurane and desflurane, comparing two anaesthesia machines, a test-lung study.

Abstract

Low-flow anaesthesia is considered beneficial for the patient and the environment, and it is cost reducing due to reduced anaesthetic gas consumption. An initial high-flow to saturate the circle system ( wash-in) is desirable from a clinical point of view. We measured the wash-in and wash-out times (time to saturate and to eliminate the anaesthetic agent, AA), for sevoflurane and desflurane, in a test-lung with fixed 3 MAC vaporizer setting at different fresh gas flow (FGF) and calculated the consumption of AA. We tried to find an optimal flow rate for speed and gas consumption, comparing two anaesthesia machines (AMs): Aisys and Flow-i. Time to reach 1 minimal alveolar concentration (MAC) (wash-in) decreased (p<0.05) at higher flow rates (1 – 2 – 4) but plateaued at 4-4.8 l/min. The consumption of AA was at its lowest around 4-4.8 l/min (optimal flow) for all but the Aisys /desflurane group. Wash-out times decreased as FGF increased, until reaching plateau at FGF of 4-6 l/min. Aisys had generally shorter wash-in times at flow rates < 4 l/min as well as lower consumption of AA. At higher flow rates there were little difference between the AMs. The “optimal FGF” for wash-out, elimination of gas from the test-lung and circle system, plateaued with no increase in speed beyond 6 l/min. A fresh gas flow of 4 l/min. seems “optimal” taking speed to reach a 1 MAC ET and gas consumption into account during wash-in with a fixed 3 MAC vaporizer setting, and increasing fresh gas flow beyond 6 l/min does not seem to confirm major benefit during wash-out.

In vitro performance evaluation of AnaConDaTM-100 and AnaConDaTM-50 compared to a circle breathing system for control and consumption of volatile anaesthetics

“…Data showed that the time to reach the target concentration did not depend on the FGF in the circle breathing system. At first instance, this observation seems unusual because flow-dependent wash-in times have been described for different anaesthetic machines by prior researchers and this further corresponds to the perception of anaesthetists in clinical practice [5,6]. However, it is known that the Aisys CS™ anaesthesia ventilator with the VA-specific Aladin™ cassette controls the VA output independent of the manually adjusted FGF.…”

“…Air (1), oxygen (2), and a vaporized anaesthetic (3) are injected through the anaesthetic machine into the circle breathing system (4). An anaesthesia gas scavenging system is connected (5). The circle breathing system is connected via a heat moisture exchanger (6) to the test lung box with two bag-valve units (BV) with a volume of 2 l each.…”

1-1-8 one-step sevoflurane-nitrous oxide wash-in scheme for low-flow anesthesia: simple, rapid, and predictable induction

“…(b) increasing FVS to induce a concentration effect [11], or (c) integrating both methods. [12]. Finally, Shin and colleagues performed a wash-in 6 study using a Primus anesthetic machine connected to a test-lung, using a FGF of 0.5, 1, and 3 L•min-1 and setting the FVS to 6%.…”

Desflurane consumption with automated vapour control systems in two different anaesthesia machines. A randomized controlled study

“…14 However, since the introduction of automated gas control delivery systems only a few studies have investigated functionality and effects on volatile anaesthetic consumption. [14][15][16][17][18][19][20] The aim of this study was to compare the consumption of desflurane delivered with and without the use of automated gas control (AGC) Flow-I or end-tidal gas control Aisys gas control delivery systems. We also compared volatile anaesthetic consumption between the two different automated anaesthetic gas control systems used in the study, the time it took to reach a minimum alveolar concentration of 0.7 and the time to reach a FGF of 0.5 L/min.…”

“…The devices ensure safe delivery of volatile anaesthetics and oxygen during low or minimal flow anaesthesia 14 . However, since the introduction of automated gas control delivery systems only a few studies have investigated functionality and effects on volatile anaesthetic consumption 14‐20 …”