Resistance to gas flow in the "new" anaesthesia circuits: a comparative study.

The resistance to gas flow is measured in the Jackson-Rees modification of the Ayre's T-piece, the "Bain" circuit, and the circle circuit using the conventionally employed rubber tubing, or either of two coaxial circle tubing systems. The Ayre's T-piece has the lowest resistance to gas flow, followed by the circle circuit with conventional rubber tubing, then the "Bain" circuit and the coaxial circle circuits. When the resistance to gas flow in the inspiratory limb is measured with a tracheal tube attached to each circuit the resistances increase in magnitude, but the differences among the circuits become less significant.