A co-axial system in which the fresh gas flows through a narrow inner tube within the outer corrugated tubing.The Bain circuit is a modification of the Mapleson D system.
- Functions in the same way as the T-piece, except that the tube supplying fresh gas to the patient is located inside the reservoir tube.
- Inspiration - The patient inspires fresh gas from the outer reservoir tube.
- Expiration - The patient expires into the reservoir tube. Although fresh gas is still flowing into the system at this time, it is wasted, as it is contaminated by expired gas.
- Expiratory pause - Fresh gas from the inner tube washes the expired gas out of the reservoir tube, filling it with fresh gas for the next inspiration.
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