The flow requirement in a non-polluting Mapleson C circuit.

Capnography and measurement of the respiratory minute volume were carried out on normal, conscious subjects during breathing of pure O2 via a Mapleson C modification of a Magill attachment, with and without continuous gas evacuation. The measurements were performed in two series, with intermittent discharge and with continuous evacuation. Rebreathing was calculated in relation to the test subject's basal respiratory minute volume, measured at the commencement of the test. The measurements indicated CO2 accumulation at a flow below 200% of the respiratory minute volume. There was no significant difference between the systems with and without evacuation.