Fresh gas decoupling valve affects the washout profile of volatile anesthetics in anesthesia workstations

Washout efficiency of volatile anesthetics may differ depending on anesthesia workstation structure, particularly the presence of a fresh gas decoupling valve (FGDV). However, this influence has not been systematically evaluated.

This in vitro study investigated sevoflurane washout in four anesthesia workstations: Fabius GS™ and KMA-1300Vi™ (with an FGDV), and Aespire™ and FLOW-i™ (without an FGDV). Three machines per model were tested. After equilibration at 2.0% sevoflurane, the vaporizer was turned off, and washout time to < 0.1% was measured at fresh gas flows (FGF) of 3-10 L/min. A mixed-effects ANOVA and linear regression analyses were performed.

A total of 96 washout trials were carried out, including four workstation models, three devices, and eight FGF levels. Washout time decreased with increasing FGF in all models. Machines without an FGDV showed rapid washout at ≥ 6 L/min, while those with an FGDV exhibited gradual decline. ANOVA revealed significant effects of FGF (p < 0.001), the presence of an FGDV (p = 0.028), and their interaction (p < 0.01). Regression analyses showed robust inverse-proportional relationships in FGDV-equipped machines (adjusted R² > 0.9), whereas those without an FGDV  deviated from this model.

The presence of an FGDV significantly alters volatile anesthetic washout behavior. Workstations with an FGDV demonstrate more predictable but slower washout, while those without an FGDV allow faster clearance at higher FGF. These in vitro findings highlight that circuit architecture, including the presence of FGDV, affects washout dynamics. Further clinical studies are needed to determine implications for emergence and contamination control.