Circle systems with a coaxial inspiratory limb. Investigation with a lung model

A laboratory study of a new circle system is presented. The inspiratory limb encloses a coaxial tube, delivering fresh gas close to the patient, immediately upstream of the inspiratory one-way valve. The system is more efficient than the non-coaxial system and allows the expiratory valve to be situated conveniently at the canister end of the expiratory limb. A disadvantage of low flow anaesthesia is the sluggish response of the system to changes in vapour or oxygen concentrations in the fresh gas flow. This is markedly improved by the new system. The advantages of the system are largely independent of respiratory pattern.