The valve comprises a Y-piece and a semi-closed and semi-open position for th circulatory system. A standard anaesthetic circulatory system can be switched between a semi-closed and semi-open position. The air exhaled by the patient is discharged near the patient into the ambient air, thereby avoiding contamination of the circulatory system by exhaled nitrogen. The patient is always pre-oxygenated with 100% oxygen within a shortened period. The four-way valve is positioned near the Y-piece of a semi-closed anaesthetic circulatory system.
