Universal F2 Breathing Circuits King F single-limb anesthesia breathing circuit introduced in 1992. Desiring to improve patient care, increase efficiency and reduce the overall cost of anesthesia delivery, King Systems developed the first co-axial rebreathing and heat and moisture conservation system in the world.Benefits of King Systems Single-Limb Anesthesia Breathing Circuits.Co-axial filter helps increases patient safety, simplifies set-up and eliminates the need for two filters.Reduces problems associated with dead space and weight.Reduces issues associated with increased flow resistance.Decreases the risk of disconnection.Compact, flexible and easy to handle.Reduces the cost of delivered inhaled anesthetics.Converts easily to a transport unit, and if necessary, to a resuscitation circuit.Helps keep patients warm and comfortable.Converts into a high flow (Bain or Mapleson) circuit with connector and fresh gas extension.