Wash-in and wash-out times required to reach the target concentration of sevoflurane in a lung model: according to anesthetic machines (Primus®, Perseus® and Zeus®) and fresh gas flow

Background and Goal of Study: To compare wash-in and wash-out times that were required to reach target concentrations of sevoflurane according to type of anesthesia machines (AM) and fresh gas flow rate (FGF) in a lung model. 
Materials and methods: Sevoflurane wash-in and wash-out times were measured on 3 AMs [Primus®, Perseus®, or Zeus®(F, fresh gas mode)] using 3 FGF (0.5-, 1-, or 3-L/min), and Zeus®(A, auto-mode) with 100% O2. AMs were connected to Test lung®, and sevoflurane was set at a 6% vaporizer setting in the Primus®, Perseus®, and Zeus®(F) or at a target end-tidal setting of 4.0% in the Zeus®(A) with mechanical ventilation. Time to reach 4% sevoflurane concentration was measured during wash-in from 0% to 6% [Primus®, Perseus®, Zeus®(F)] or 4% [Zeus®(A)]. Time to reach 1% sevoflurane concentration was measured during wash-out from 4% to 0%. Results and discussion: With different FGF rates in same type of AM, wash-in and wash-out times shortened with the increasing FGF rates (P < 0.05). Wash-in and wash-out times was shorter in the order of Perseus®, Primus®, and Zeus®(F) in all FGF groups (P < 0.05) excepted for wash-out time using 0.5-L/min for which order was Perseus®, Zeus®(F) and Primus® (P < 0.05). For both Zeus® modes, wash-in time in Zeus®(A) was shorter in FGF rate 0.5- and 1-L/min groups of Zeus®(F), but longer in FGF rate 3-L/min group of Zeus®(F) (P < 0.05). Wash-out time in Zeus®(A) was shorter than that of Zeus®(F) in all of FGF groups (P < 0.05). 
Conclusion(s): Rapid changes of target sevoflurane concentration were associated with high FGF rate, use of blower-driven ventilator, small internal breathing volume, absence of a decoupling system, and proximal fresh gas inlet to patient of AM.

Wash-in and wash-out times required to reach the target concentration of sevoflurane in a lung model: according to anesthetic machines (Primus®, Perseus® and Zeus®) and fresh gas flow